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Essay 316 - Twin pregnancy

Posted by Sarika N.
healthy 34 year old woman underwent in-vitro fertilisation for unexplained sub-fertility and two embryos were replaced. She is found to have a twin pregnancy at 6 weeks gestation. (a) Discuss how you would establish chorionicity [5 marks].
All women with twin pregnancies should be offers USS preferably transvaginal between 10 and 13 weeks of gestation to diagnose chorionisity, viability, major abnormalities and nuchal translusency.
Chorionicity is very accurate before 14weeks, presence of T-sign is a diagnosis of monochorionic twins, when presence of lamda sign - dichorionic twins. Preferably, photographic records should be retained and if there is any uncertanty the patient should be send for a second opinion to the specialist centre.
(b) Discuss the additional risks associated with monochorionic twin pregnancies when compared to dichorionic twin pregnancies [5 marks].
MC twins have high incidence of fetal mortality, especially in the second trimester mainly due to twin-twin transfusion syndrome.
Birth weight is less in monochorionic twins and incidence of preterm deliveries is higher in monochorionic twins. Also monochorionic twins have increased risk of neurodevelopmental morbidity. Discordant fetal growth restriction not due to TTTS ( differentiated by absence of polyhydramnious) is more difficult to manage in monochorionic pregnancies. After the single fetal death the risk to the surviving twin of death is much higher in monochorionic pregnancy. There is a risk of cord entaglement in MCMA twins and early at 32 weeks delivery is recommended.
(c) She is found to have a monochorionic twin pregnancy. Discuss and justify your schedule of ultrasound assessment of the fetuses [6 marks].
The fetal ultrasound assessment should be performed every 2-3 weeks in uncomplicated monochorionic twin pregnancies from 16 weeks. USS between 16 and 24 weeks is aimed to detect TTTS , after 24 weeks is to detect grwth restriction or discordant growth.
Before 24 weeks USS assessment should include AC, brain image, liquor volume in both sacs ( to exclude oligo or polyhydramnious). After 24 weeks umbilical artery dopplers should be added to assess fetal well being. In complicated twin pregnancy, especially by TTTS the timing of USS should be discussed on individual basis but at least weekly monitoring should be done. Fetal detailed cardiac scan including should be part of antenatal monitoring.
(d) What are the options for managing twin to twin transfusion syndrome presenting at 20 weeks gestation? [4 marks].
Twin-twin transfusion syndrome should be managed in the specialist fetal medicine centre.
The couple should be appropriately counselled regarding the complications of the condition, available options and the risks involved.
Severe TTTS before 26 weeks should be treated by laser ablation, rather than by amnioreduction or septostomy acxcording to Eurofetus and NICHD trials. The risks are the death of one or both babies and neurological abnormalities. Also there is a risk of reccurence.
In severe cases termination of pregnancy could be discussed as an option. Another option is selective termination if severe hydrops fetals or severe brain damagein one of the twins, could be done by using bipolar diathermy of one of the umbilical cords.
Parents should have appropriate information and counselling to make an informed decision.
Posted by H H.
Chorionicity can be established via an experienced ultrasonographer, usually in fetal medicine unit, preferabllly at gestational age less than 14 weeks.( from 11 to 14 wk best).
In dichorionic twins DCT, the Lambda sign can be detected (show thickening of membrane between the two sacs). In monochorionic twins MCT, the T sign is detected ( thin membrane between the two sac which forms the shape of T with the placenta ).
If there is no membrane seperating the sacs ,it is monochorionic mono amniotic MC MAT.


MCT are associated with increased perinatal morbidity and mortality when compared to DCT.
There is an increased risk of discordinate growth of both twins( Detected when the difference of fetal growth is >20%). There is increased risk of twin to twin transfusion TTT. This occurs through an arterio venous anastmosis between both fetal circulations, so in the donner twin we will find growth restriction, fetal anemia and oligo hydramnios, and in the recepient there is macrosomia, polycythemia ,heart failure and poly hydramnios. Acute hydramnios can occur and can present as an emergency associated with severe pre eclampsia and need prompt management. Premature delivery is more likely with MCT and this is associated with problems of prematurity in neonates.
There is the possibility that one of the twins might die and this would cause neurological damage in the surviving twin due to cross circulation.
I n MCMAT , there is an increased risk of fetal death in utero due to cord entangelment. Congoint twins can occur with risks occuring at delivery and future seperation after delivery.


A dating scan is done at an early gestation for accurate detection of gestational age ,which is important for accurate assessment of screening tests for chromosomal abnormalities ( nuchal thickness NT) ,or structural abnormalities eg alpha feto protein in neural tube defects NTD( this has been replaced by ultrasound for detection of NTD which has higher sensitivity and specificity in detection of this when done between 18 to 21 WK)
A scan at 13 wk is done for NT measurement which is best time for its measurement. At this scan chorionicity can also be detected.
Growth scan is schadueled from 18 wk and done every two weeks , for the detection of dicordinate growth and early detection of TTT.
A detailed scan at 20 to 22 wk is done for detection of congenital malformation. An echo cardiograph can also be done at same time for cardiac abnormalities.
Doppler blood flow of middle cerebral artery to detect if there is fetal anemia of one of the twins. Hltrasound can help when any invasive procedure, used in managing the patient, to localise the site of the placenta and to avoid injury of fetus.



These options are done at fetal medicine unit. Ablation of arteriovenous anastmosis with laser lead to increased survival in twins with TTT, and gave better results than septostomy, however not all anastmosis are occluded and TTT can still occur.
Making an opening in the membrane seperating the twins(septostomy) will lead to equilibration of pressure between the two sacs but will not prevent the process.
Aspiration of amniotic fluid from the sac with polyhydramnios will lead to maternal comfort, but will not prevent re accumilation and need to repeat the process . There is also risk of infection and rupture of membranes.
Selective fetocide via occlusion of the cord of one twin is associated with stoppage of the process, but one should counsell patient first and is associated with guilt and regret.
In patients presenting with acute polyhydramnios, or patients not willing to continue with the pregnancy, ending the pregnancy is an option.

Posted by ASB -.
ASB
(a) Chorionicity is established by ultrasound (US) examination. US before 14 weeks gestation has a higher sensitevity and specificity in establishing chorionicity compared to US examination after 14 weeks . Inspection of the site of attachment of intertwin membrane with the placenta may show \'lambda\' or \'twin-peak\' sign (a triangular piece of placental tissue extending into the intertwin membrane ) with dichorionic ( DC) twins but \'T-shape\' with monochorionic (MC) twin. In addition the intertwin membrane is thicker wit DC twins than with MC twins . Discordant fetal sex is a feature of DC twins . Visualisation of 2 separate placentae indicate DC twins.

(b) Twin to twin transfusion syndrome (TTTs) occurs only with MC twins . It is due to unbalanced unidirectional arteriovenous anastomosis resulting in shifting of blood from one twin (donor) to the other twin (recepient) with consequent growth restriction and oligohydramnios in the donor and polyhydramnios and later on hydrops in the recepient .
Another specific problem is that in utero death of one twin in MC pregnancy result in acute transfusion of blood from the surviving twin to the dead one . This result in death and ischaemic brain injury in 13% and 18% respectively of surviving twins .
Monoamniotic pregnancy (occurs only with MC twins ) is associated with 35-50% risk of perinatal mortality due to cord entanglment.

(c)Dating scan between 10 and 13 weeks gestation enable accurate estimation of gestational age , confirm viability , determine chorionicity ,detect major congenital fetal malformations and measure nuchal translucency.
From 16 weeks onward , US to be scheduled every 2-3 weeks with aim of detection of TTTs between 16 and 24 weeks gestations . At 18-20 week , detailed anomaly scan for detection of congenital anomalies. The aim of US after 24 week is detection of growth retardation with measurment of abdominal circumference , head circumference , maximum pool depth of both sacs and umblical artery doppler

(d)serial amnioreduction means serial aspiration of amniotic fluid from the sac with polyhydramnios to decrease amount of amniotic fluid volume . Laser ablation of placental anastomosis aims at interruption of vascular anastomosis between the 2 fetuses . Compared to amnioreduction , it is associated with fewre death of both fetuses and more babies alive without neurologic abnormality at 6 month age . However , it may miss anastomosis and later recurrence of TTTs occurs in up to 14 %of cases . Selective feticide sacrify one twin to allow better chance for the co-twin to survive . It occlude one umblical cord using bipolar diathermy or coils . Septotomy is a deliberate creation of a hole in the intertwin membrane aiming at improving the amniotic fluid volume in the donor sac.
Posted by SYAMALRANJAN S.
(a) Discuss how you would establish chorionicity [5 marks].

I would offer scanning to establish chorionicity at 11-14 weeks of gestation. Identification of `lamda’ or twin peak sign characteristic of dichorionic twin and `T’ sign is characteristic of monochorionic twin at membrane-placenta interface . Sensitivity is about 90% and specifity is 99.5%. These figures are lower beyond 14weeks. Photographic record should be retained in the notes. It can be diagnosed in non-tertiary centre. Any uncertainty, she should be referred for specialist assessment as soon as possible

(b) Discuss the additional risks associated with monochorionic twin pregnancies when compared to dichorionic twin pregnancies [5 marks].

The risk of twin-to twin transfusion(TTTS) syndrome affects 15% of monochorionic twin pregnancies and are increased risk of cardiac anomalies. Other risks such as oligohydranios ,absent bladder filling, renal failure in donor twin and cardiac hypertrophy, hypertension, polyhydramnios in recipient twin are also high. Discordant growth and fetal malformation risks are high compared to dichorionic twin. Risk of death of surviving twin in case of co-twin death (about 12%) and neurological abnormality (about 18%) are high. Higher fetal loss which includes late miscarriages, intrauterine death, still-birth rates compared to dichorionic twin

(c) She is found to have a monochorionic twin pregnancy. Discuss and justify your schedule of ultrasound assessment of the fetuses [6 marks].

Experienced fetal medicine expert should be involved for ultrasound assessment. At 11-14 weeks, ultrasound assessment of gross congenital anomalies and nuchal translucency measurement could be done. After that from 16 weeks gestation 2-3 weekly interval of fetal assessment in uncomplicated pregnancy would be arranged. Then at 20 weeks detailed fetal anomaly scan and fetal cardiac scan at 22-24 weeks. TTTS diagnosis from 16 to 24 weeks should be aimed(monochorionic placenta or single placental mass,oligohydramnios in one sac and polyhydramnios in other, concordant gender, discordant bladder appearances and haemodynamic / cardiac compromise in severe TTTS). After 24 weeks TTTS presentation is uncommon and focus for growth scan ( restriction). Assessment should includes abdominal circumference, brain imaging , head circumference, liquor volume and umbilical artery Doppler after 24 weeks.
(d) What are the options for managing twin to twin transfusion syndrome presenting at 20 weeks gestation? [4 marks].
Management is to be done in regional fetal medicine unit. Severe TTTS presenting before 26wks should be treated by laser ablation( laser photocoagulation, better perinatal outcome compared to amnioreduction). Other options are amnioreduction and septostomy (no significant difference in outcomes when both are compared). Selective feticide by cord occlusion is another effective option. The option of no treatment or termination of pregnancy should be discussed. Following treatment weekly ultrasound assessment, corticosteroid administration, delivery at 34 weeks(usually by CS) should be planned.

Posted by SRABANI M.
SM
a. All women with a twin pregnancy should be offered an USS at 10-13 wks of gestation to assess viability, chorionicity, major conjenital malformation & nuchal translucency.It is essential to determine chorionicity as soon as a twin pregnancy is diagnosed. In USS Monochorionic twin can demonstrate ‘ T sign ‘ at the membrane –placenta interface. Dichorionic twin demonstrates Lambda sign or twin peak sign ( remnant of chorion leave).Chorionicity determination is upto 100% accurate in first trimester & 80-90% accurate in second trimester.Different sex twin & different placentae also suggeset dichorionicity, although 3% of monochorionic twin may have bipartite placenta but they are not dichorionic. Chorionicity is better determined before 14 wks than after 14 wks of gestation.If there is any uncertainty about chorionicity, a second openion should be saught. If there is any doubt in diagnosis of chorionicity, she should be referred to specialist without delay.A photographic record should be kept in her notes of the USS appearance of membrane attachment to the placenta.

b. Additional risks associated with monochorionic twins are increased mortality & morbidity from acute hydromnios, congenital anomalies, intrauterine death & twin- twin transfusion syndrome.The risk of late miscarriage & perinatal mortality are increased in monochorionic than dichorionic twins.In monochorionic twin there is higher chance of neurodevelopmental morbidity and higher fetal loss rate ( 26%) than dichorionic twins.Twin to twin transfusion syndrome is the main cause of fetal loss mainly upto 24 wks.Also monochorionic monoamniotic pregnancies carry a very high risk of cord entanglement.

c. If she is found to have monochorionic pregnancy, she will have regular USS in every 2-3 wks from 16 wks of gestation in uncomplicated pregnancies till 24 wks . USS between 16-24 wks mainly focuses on detection of Twin – twin transfusion syndrome. After 24 wks first presentation of TTTS is very uncommon & hence she will have USS after 24 wks according to local protocol. Frequency of scan may vary from weekly to monthly in different trusts.This USS mainly to detect fetal growth restriction. In monochorionic twins detailed USS will include views of fetal heart .In severe TTTS , a fetal echocardiography is considered.Also umbilical artery Doppler study is recommended after 24 wks in monochorionic twins.It may show reversed or absent end diastoloic velocities in umbilical artery Doppler & these are more common in discordant growth restriction than uncomplicated or severe TTTS.

d. TTTS should be managed in regional fetal medicine centre with appropriate specialist expertise. Severe TTTS should be treated by laser ablation if they present before 26 wk of gestation.Other options are amnioreduction and septoplasty but laser ablation is preffered before 26 wks.Termination of pregnancy is another option in severe TTTS if the woman requsts for it. Selective termination of pregnany can be another option in severe hydrops fetalis or cerebral damage in either
Posted by L S.
LS:
(a) Discuss how you would establish chorionicity [5 marks].
Chorionicity is best established by performing an ultrasound at 11-14 weeks of gestation as it has been shown to be both sensitive (90%) and specific (99.5%). Both sensitivity and specificity decreases with increasing gestations. All dizygotic (two embryo) twins are dichorionic. However monozygotic twins (division of a single embryo) can be either dichorionic or monochorionic. Presence of two placental mass and lambda sign (placental-membrane interface thickening) is the most accurate predictor (almost 100% specific) for dichorionic twins. Monochorionic twins will have single placental bed with absence of lambda sign. Monochorionic twin will have ‘T’ sign where the membrane reaches the placenta at 90 degrees. I would take a photograph of scan finding of appearance of attachment of membrane to placenta and retain in patients notes. I will seek second opinion with the photograph taken if I am not sure of diagnosis of chorionicity. I would refer her to a specialist without delay for confirmation of chorionicity before 14 weeks.

(b) Discuss the additional risks associated with monochorionic twin pregnancies when compared to dichorionic twin pregnancies [5 marks].
The additional risk include Twin-to-twin transfusion syndrome (TTTS) which is due to the disproportionate blood supply in the placental mass to each fetuses resulting in one twin being smaller (donor) with oligohydramnios and the other twin (recipient) being bigger with polyhydramnios. Consequences to the co twin if one twin dies is also more severe. Here the risk of death of the surviving twin is 12% and the risk of neurological abnormality is 18%. If the twins were found to have discordant fetal malformations, their management can be difficult and option of selective fetocide by intracardiac injection of potassium chloride cannot be offered due to presence of anastomoses between fetuses. If the monochorionic twin was found to be also monoamniotic (no dividing membrane, both fetuses in one sac only) these twins are at risk of cord entanglement. Monochorionic twins have higher complication rate than dichorionic twin pregnancies and are known to have higher fetal loss rate.

(c) She is found to have a monochorionic twin pregnancy. Discuss and justify your schedule of ultrasound assessment of the fetuses [6 marks].
Her first scan should be for fetal viability, dating (further routine scan and antenatal care planning), chorionicity (planning for early detection and management of complications like TTTS), gross congenital abnormality excluded. During her first scan which is at 11-14 weeks she should also be offered nuchal translucency (NT) measurements if she wishes to have Downs syndrome screening. NT has similar sensitivity as singleton but specificity is lower in monochorionic twins which may reflect difference in placental supply to each twin. Marked discrepancy in NT measurements although can be highly suspicious of TTTS its value remains unclear with varying studies demonstrating varying specificity and sensitivity. She should be seen 2 to 3 weekly for fetal assessment from 16 weeks primarily for detection of TTTS between 16-24 weeks. Earlier detection of severe TTTS will allow earlier intervention with option of treatment by laser ablation which can be offered before 26 weeks by fetal medicine team at regional center. Laser ablation has been proven to improve perinatal outcome when compared to amnioreduction in severe TTTS. Detailed anomaly scan at 20 weeks should be scheduled to include extended views of fetal heart as congenital heart disease, neural tube defects and hydrocephalus was found to occur more frequently in twins. After 24 weeks TTTS as first presentation is uncommon and focus from here on should be for fetal growth restriction (concordant or discordant). No clinical trials has been carried out on frequency of monitoring after 24 weeks (weekly or 2, 3, 4 weekly) to decide on which is the most effective schedule for early detection of complication and the most cost effective. During fetal assessment should include abdominal circumference, brain imaging with/without head circumference, liquor volume, umbilical artery Doppler after 24 weeks for fetal well being.

(d) What are the options for managing twin to twin transfusion syndrome presenting at 20 weeks gestation? [4 marks].
This pregnancy should now be treated in a regional fetal medicine center. Laser ablation via photocoagulation of anastomosis can be offered if TTTS found to be severe. Recurrence risk of 14% due to missed anastomosis at laser ablation can occur. Amnioreduction of recipient (polyhydramnios) twin can be offered but will require repeated procedures as amniotic fluid reaccumulates. The other option is septostomy by making hole in the inter-twin membrane to increase amniotic volume of donor (oligohydramnios) twin. Selective fetocide by cord occlusion can minimize perimortem inter-fetal transfusion can be offered in stage III/IV (Quintero classification) TTTS or as an alternative to laser ablation. Termination of pregnancy with no treatment can also be an option and should be discussed with couple. Once treatment carried out, weekly ultrasound assessment should be performed. Antenatal steroids administered once viability attained. Delivery by caesarian section considered once reached 34 weeks gestation.
Posted by Chitra.s M.
A.Chorionicity of twin pregnancy is best established by ultrasound examination before 14 weeks gestation.The woman is offered as ultrasound examination between 11-13 weeks gestation ,preferably by a fetal medicine specialist.The diagnosis is based on the presence of \'twin peak \' sign or the \'lambda\' sign at the membrane placental interface denoting a dichorionic gestation.The presence of T sign indicates a monochorionic gestation.The usg assessment of chorionicity is highly accurate though not 100% sensitive.If there is a doubt regarding chorionicity she is referred for a second opinion& photographic record of the ultrasound appearance of membrane attachment to the placenta should be retained in the case notes.

B.Monochorionic twins(MCT) are at a higher risk of perinatal morbidity & mortality compared to dichorionic twins(DCT).This is mainly due to 2nd trimester loss.The mean birth weight & gestational age at delivery is also less for MCT as compared to DCT.10-15% of monochorionic pregnancies can be complicated by twin to twin transfusion(TTTS).This is more common in MC diamniotic geatation compared to MC monoamniotic gestation.This is more likely in pregnancies having an unidirectional placental artery-vein anastamosis.MC twins are at a higher risk of neuro developmental morbidity .Death of co-twin in MC twins may lead to heamodynamic changes in the surviving twin causing end organ damage especially the brain.MC twins are also at an increased risk of discordant abnormalities including twin reversed arterial perfusion sequence.monoamniotic twins are at an increased risk of cord entanglement & higher risk of perinatal mortality & morbidity.
C.The woman is referred to fetal medicine specialist .The woman is offered an ultrasound examination (USG) between 11-14 weeks nuchal translucency(NT) for fetal aneuploidy screening.The role of NT screening in predicting TTTS is not clear.She is offered usg every 2-3 weeks from 16 weeks gestation.Serial scans between 16-24 weeks gestation is aimed at detection of TTTS.at each usg, the maximum amniotic pool depth in each sac, abdominal circumference, brain imaging & umbilical artery dopplers of both twins are carried out.This is done for early detection of TTTS.A detailed anomaly scan of both fetuses is done
at 20-22 weeks gestation with extended views of fetal heart. In the presence of TTTS fetal echocardiography may be offered to assess the severity.
USG is offered every 2-3 weeks or according to unit protocols after 24 weeks.This is for monitoring of fetal growth & well being.Although new onset TTTS is rare after 24 weeks,this is looked out for during each scan.
D.TTTS must be managed in a fetal medicine unit .Management depends upon the severity of TTTS, facilities available and maternal wishes.Severe TTTS can treated by laser ablation of anastomosis, amnioreduction or septostomy.Laser ablation is preferred since it results in lower incidence of perinatal mortality & morbidity & more surviving babies without neurological impairment when compared to amnioreduction.The option of termination of pregnancy is discussed if the woman wishes so. another option would be to offer selective termination if one twin is severely hydropic or shows evidence of brain damage.This would involve diathermy of the umbilical cord of the affected twin.
Posted by S S.
a. Establishing chorionicity is important as complication rates are higher in monochorionic pregnancies as compared to dichorionic. This is best done before 14 weeks. Demonstrating a lambda (dichorionic) or T sign (monochorionic) between placenta and membrane on ultrsound between 10-13 weeks is one method. Alternatively, membranes can be counted. Presence of 4 membranes is suggestive of dichorionic placentation and <4 membranes, monochorionic. Assesing the thickness is another way of diagnosing chorionicity. Later in pregnancy, discordant sex and presence of two placentae implanted away from each other indicate dichorionic pregnancy. Photographic record should be kept and if in doubt referral to regional fetal medicine unit should be made.
b.Complications of monochorionic twins are due to placental vascular anastomosis like twin to twin transfusion syndrome is more common in monochorionic twins, consequences of death of co-twin on surviving twin are more severe in monochorionic than dichorionic. Twin reversed arterial perfusion sequence affects monochorionic pregnancy. Monochorionic pregnancy has higher fetal mortality due to second trimester losses. Cord accidents occur in monochorionic monoamniotic twin pregnancy.
c. Monochorionic pregnancy is at higher risk of fetal complications hence require frequent fetal monitoring. Ultrasound scans are done every 2-3 weeks starting from 16 weeks to detect twin to twin transfusion syndrome and after 24 weeks to detect growth restriction. At each visit ultrasound scan includes measuring AC, maximum pool depth brain imaging with or without head circumference, identifying the dividing membrane, studying each cord separately and doing the umbilical artery dopplers.
d. Referal to the regional fetal medicine unit should be done. Before 26 weeks it is beast managed by laser ablation of anastomosing vessels as it is associated with fewer perinatal and neonatal deaths and neurological abnormalities as compared to amnioreduction and septostomy. However the treatment depends on facilities and experties available, severity of the condition as well as parental wishes. Hence other options are serial amnioreduction from polyhydramniotic sac, septostomy, termination of pregnancy or selective termination after bipolar diathermy of umbilical cord especially if hydrops is recurrent or there is evidence of cerebral damage.
Posted by Bindi J.
BJ:

Chorionicity is established by ultrasound. This should be performed between ten and thirteen weeks of pregnancy for accurate assessment. Though ultrasound assessment is very accurate, it does not have 100% sensitivity. Determination of chorionicity is important to allocate risk and have a management plan for the rest of the woman’s pregnancy. Ultrasound diagnosis is based on demonstration of twin peak or lambda sign for dichorionic(DC) twins and T sign for monochorionic twins(MC). These signs are looked for at placenta –membrane interface. A photographic record of the ultrasound appearance of membrane attachment to placenta should be retained in the case notes. If there is uncertainty as to the chorionocity, second opinion should be sought. If there is a doubt in the diagnosis of chorionicity then the woman should be referred to a specialist without delay. This must be conveyed to the woman. Discordant gender is a pointer to dichorionicity.

MC twins are at higher risk of morbidity and mortality compared to DC twins because both babies are dependent on a single shared placenta. MC pregnancies have higher fetal loss rates (25%) compared to DC pregnancies. They have a greater propensity to renal and neurological lesions. The risk of cerebral palsy is higher in surviving monochorionic twin. This appears to be due to placental vascular anastomoses. Twin reversed arterial perfusion sequence (TRAP) is found in 1% monochorionic pregnancies. It is rarely found in dichorionic twins. It is characterised by an acardiac twin who receives its blood supply from normal pump co twin via a large arterio arterial anastomosis. Twin twin transfusion syndrome(TTS) is found in monochorionic monoamniotic(MCMA) as well as monochorionic and diamniotic(MCDA) pregnancies. MCMA pregnancies carry a high risk of cord entanglement.

Fetal ultrasound assessment should take place every 2-3 weeks in uncomplicated MC pregnancies. This should be started from 16 weeks. This information should be clearly communicated to the patient and documented in her notes. Ultrasound examination between 16 and 24 weeks focuses primarily on detection of TTS. After 24 weeks, TTS presentation is uncommon. The main purpose of subsequent scans is to detect fetal growth restriction. The scan should include abdominal circumference measurement, imaging of fetal brains and maximal vertical pool depth. In addition, all MC twins should have a detailed ultrasound scan which includes extended views of the fetal heart.

The woman should be approached sensitively and diagnosis should be explained to her along with the implications. She should be referred to a regional Fetal Medicine centre with recourse to specialist service. The course of the condition is unpredictable. Quintero system has got a good prognostic value in TTS staging. Options are offered depending on severity. The options are conservative treatment, termination of pregnancy or selective termination of pregnancy. The woman should be supported in her decision. If she opts for conservative treatment, laser ablation is preferred. Following laser ablation, more babies are alive without neurodevelopment delay. Success is 50-65%. However, some anastomoses may be missed resulting in recurrence of TTS. Then there is a scope for septoplasty or amnioreduction. For mild to moderate TTS, serial amnioreduction has a success of 60-65%. Septoplasty has a success of 85%. Selective fetal termination can be done by bipolar diathermy of one of the umbilical cords. There should be clear documentation in the notes of this discussion. Written information should be provided.






Posted by drvimaladkm@yah K.
a)I would establish the chorionicity by ultrasound which is 100%sensitive for diagnosis if done within first trimester of pregnancy.Second trimester scan is 80 to 90% sensitive in diagnosing chorionicity.Monchorionic twin is diagnosed by “T” sign where as dizygotic by “Twin peak or Lambda” sign due to thickened intervening septum. Monochorionic is difficult to diagnose sometimes & may require doppler or colour Doppler at the interphase of chorion & membranes. Sex of the twins are of the same gender. Histology is also similar in both twins in monochorionic twin. Vascular anastomosis and sharing of the placenta indicates monochorionicity. Family H/O monochorionic twin is constant as 1 in 300.
b) Monochorionic twins has more risks compared to Dichorionic twins.Both types of twins has increased risk of Premature babies more so with monochorionic ending up at lesser gestational age compared to Dichorionic. Prematurity is the major contributor for perinatal mortality(about 10%). Maternal risks like hyperemesis gravidarum, preeclampsia, Gestational Diabetes, Polyhydramnios , overdistention Postpartum haemorrhage are common to both types of twins. Miscarriage is increased in frequency in monochorionic pregnancy. Vanishing twin with disappearance of one twin at early gestational age can also occur in monochorionic twin without much risk to the mother. Fetal death in utero late in 2nd trimester or in 3rd trimester may give rise to neurological sequelae or cerebral palsy in the surviving twin due to hypotension and ischemia. Fetal growth restriction and discordant twin are more common in monochorionic than Dichorionic. Twin to twin transfusion syndrome(TTTS) can occur in ~15% of monochorionic due to Arteriovenous anastomosis with unidirectional flow has poorer prognosis. It is commonly found in monochorionic diamniotic twin. Twin reversal arterial perfusion(TRAP) occurring in 1% of monochorionic can give rise to acardiac twin due to large arterial arterial anastomosis with normal pumptwin. Congenital anomalies are also increased in monochorionic with increased neuraltubedefects, cleftlip& cardiac anomalies & holoprocencephaly due to vascular disruptions. Conjoint twins are monochorionic twins due to late division (after8days) producing dystocia,obstruction & rupture during labour. Cord accidents and cord entanglements can occur with battledoor cord insertion, may increase sudden foetal deaths in monochorionic twins.
c)Monochorionic twin ultrasound assay has to be done in early pregnancy as dating scan followed by at 14 weeks for Nuchal thickness of twins as prenatal diagnosis for down’s syndrome. Though it is difficult it is a better noninvasive investigation as other components of Integrated tests are subjected to alteration in values due to multiple pregnancy.Chorionic villous biopsy and amniocentesis with indigocarmine can be done in the twins without increase in risks of miscarriage. From 16 weeks of gestation monochorionic twins has to be followed up fortnightly looking for complications such as discordant twin with difference >20% in fetal biometry indicating TTTS. One sac may be having polyhydramnios with maximum vertical pool(MVP) of 8cm & other having <2cm with oligohydramnios.TTTS is also diagnosed by concordant gender & discordant bladder. Lower grade Quintero classification may not indicate good prognosis due to sudden deterioration.At 20 to 22weeks fetal echocardiography to be done by Fetal medicine dept for detection of cardiac anomalies. Uterine Doppler with persistent notch may be a predictor of preeclampsia.At 32 weeks fetal weights, lie, presentation and placental location has to be done for further management of delivery. Ultrasound may be required in labour room for confirmation of presentation of 1st ,more so of 2nd twin vaginal delivery.
d)Options for managing twins with TTTS at 20 weeks pregnancy is Laser ablation of communicating vessel, Serial amnioreduction, Septostomy, Selective feticide or Termination of pregnancy depending on patients wishes, available facilities in a tertiary centre & available technical skills. Laser ablation of the vessel may give permanent relief with ~65% success. Risk of 14% recurrence may be due to missing anastomotic vessel. Serial amnioreduction is more commonly done with risk of sepsis and fetal loss.Septostomy is to create a hole in the septum in order to increase amniotic fluid volume in the donorsac. Selective termination of a twin is done by bipolar diathermy of umbilical cord allowing a healthy twin to grow with risk of spontaneous loss of surving twin.Selective feticide with potassium chloride can not be done. Patient may chose termination of pregnancy as option.
VDKM
Posted by Lilantha W.
(a) Chorionicity is best established by a either first trimester or early second trimester ultrasound scan. Expertise and trans-vaginal scan may be required in difficult cases, especially high BMI. If a two widely separated sacs noted, it should be a dichorionic pregnancy (DCP). Similarly, two clearly separate placente indicates DCP. If two pregnancy sacs contain foetuses of different sex, it confirms DCP. When the inter-twin membrane is traced down to its insertion into the placental surface, it may either be separated into two at its insertion, demonstrating the lambda sign; or without separation , straight insertion into the peripheral membrane showing a the ‘T’ sign. A clear lambda sign is confirms DCP whereas, absent lambda sign before 14 weeks is a diagnostic of monochorionic pregnancy (MCP). ‘T’ sign is diagnostic of a MCP. When there is no inter twin membrane, it is a MC-mono-amniotic pregnancy. Usually, a combination of these objective evidence is used to determine the chorionicity.

(b) In the antenatal period, twin-to-twin transfusion syndrome (TTTS) is the most important complication where aberrant vascular anatomises or arterio-venous malformations in the placenta which results in redistribution of blood circulation. This results in transfusion of blood from one twin (doner) to the other (recipient). The doner twin would usually be anaemic, growth restricted with oligohydramnios and its sac may be pushed out nearer either to the uterine wall or to the placenta which would appear ‘stuck’ to it. In extreme circumstances, it may disappear resulting in ‘vanishing twin’ syndrome. Acardiac twin with twin reversed arterial perfusion is another complication. The recipient is usually more vulnerable with high output cardiac failure with polycythemia, macrosomia, polyhydramnios. Discordant twin growth is commoner in MCP. Signs of hydrops foetalis such as pleural effusions, ascites, pericardial effusions would develop if not treated well. In extreme circumstances, the recipient may die of cardiac failure. Demise of one twin would increase risks of pre term delivery with consequences of prematurity such as cerebral palsy, respiratory distress syndrome or miscarriage. Rarely, maternal compromise may occur due to disseminated intravascular coagulation. There is an increased risk of caesarean delivery. MC twins are at a high risk of iatrogenic injury due to foetal surgery or selective amniotic/foetal reduction than DC twins. During labour MC twins are at higher risk of cord entanglement. The risk of locked head is higher than DC twins. Conjoined twins is an extremely rare complication.

(c) Assuming the 6 weeks scan has confirmed gestation and viability, another scan is organised at 11-14 weeks. This scan is aimed to detect the nuchal translucency, if patient wishes to be screened for aneuploidy; bi-parietal diameter for accurate dating of pregnancy; chorionicity and any foetal anomaly which includes early signs of TTTS. If any signs of TTTS found, fortnight scans are indicated until delivery. If not, I would organise another scan at 14-16 weeks. A detailed anomaly scan is organised 18-20 weeks. This is expected to visualise foetal brain which includes ventricles, spine, four cardiac views, lungs, anterior abdominal wall including the cord insertion, bowel echos, kidneys, bladder, face and limbs for anomalies. Placental site is recognised to rule out a low-lying placenta. A foetal echocardiogram is organised at 20-22 weeks to recognise cardiac lesions and to measure the cardiac outputs. A full foetal biometry which includes head & abdominal circumferences and liquor volume scans are done every 2 weeks until delivery along with umbilical artery (UA) dopplars. UA dopplers would be done weekly, if any TTTS develops. The middle cerebral artery and ductus venosus dopplers may be required, if foetal anaemia develops or delivery is indicated.

(d) If both foetuses are viable, selective ablation of vascular malformation can be considered in a tertiary foetal medicine unit with the use of laser. Although diathermy had been used for this purpose, laser treatment by experts is safer and carries good prognosis. Selective feticide by cord occlusion is reserved for refractory cases. If severe anaemia encounters even after laser ablation in the doner twin, it may require a foetal blood transfusion. Serial amnio -reduction mainly provides symptomatic relief for the mother whereas, septostomy of the inter-twin membrane allows equilibration between two amniotic sacs. Expectant management with or without extensive foetal surveillance is another option. The main benefit of ultrasound monitoring of the pregnancy (surveillance) is that foetal complications can be detected sooner, providing means of timely management and delivery. Timely caesarean delivery after administration of Betamethasone 12mg IM two doses 24h apart would be the aim for majority after 24 weeks. However, termination of pregnancy after feticide is an option, particularly if other serious foetal malformations coexist. Extensive counselling by experienced professionals are important before offering these options.
Posted by Mark C.
a) Two seperate gestational sacs seen on scan would confirm the presence of DCDA twins. With one gestational sac visible this would be a monochorionic twin pregnancy. Two visible amniotic sacs mean MCDA whereas one common amniotic sac means MCMA.

b) Monochorionic twins are associated with more congenital defects compared to DCDA twins, although the rate of chromosomal anomalies do not differ. There is also risk of TRAP syndrome (where a normal twin perfuses and acardiac twin, the pump twin associated with risk of IUD and congenital defects), twin-to-twin transfusion syndrome (where due to abnormal anastomoses in the placental bed one twin loses blood to its recipient twin with both having increased risk of IUD and congenital defects). Should a twin in a monochorionic pregnancy die the other has an increased risk of IUD compared with DCDA where the second twin is rarely effected.

c) She would need a nucchal scan between 12 and 14 weeks to assess for chromosomal defects. Another scan between 14 and 18 weeks to assess for the presence of TTTS. An 18 - 22 week anomaly scan is needed at a tertiary referral centre to assess for any congenital anomaly. If any congenital anomaly is detected a fetal echo is also indicated. 2-4 weekly growth scans are required after 24 weeks to assess for equal growth and ensure well being of both twins.

d) Referral to a tertiary centre is indicated. The options include repeated amniocentesis and liquor drainage from the recipient twin until viability, when bethamethasone or dexamethasone can be given and delivery in a specialized unit advised. Otherwise laser ablation of the anastomosis in the placental bed can be performed in a tertiary unit. In this case regular follow up by once weekly scan to assess for fetal well being, steroids given after 24 weeks but aiming to deliver at about 32 weeks.
Posted by Harry B.
HB

A healthy 34 year old woman underwent in-vitro fertilisation for unexplained sub-fertility and two embryos were replaced. She is found to have a twin pregnancy at 6 weeks gestation. (a) Discuss how you would establish chorionicity [5 marks]. (b) Discuss the additional risks associated with monochorionic twin pregnancies when compared to dichorionic twin pregnancies [5 marks]. (c) She is found to have a monochorionic twin pregnancy. Discuss and justify your schedule of ultrasound assessment of the fetuses [6 marks]. (d) What are the options for managing twin to twin transfusion syndrome presenting at 20 weeks gestation? [4 marks]

A) The chorionicity can be determined in most cases by an ultrasound scan before 14 weeks. In monochorionic twin pregnancy, presence of both fetuses in one sac, conjoined twins are diagnostic of monochorionic and monoamniotic (MCMA) pregnancy and the presence of a thin interdividing membrane between the two sacs and ‘T sign’ at the membrane placental interface. The dichorionic pregnancy is characterized by a thick membrane and the presence of a lambda sign or twin peak sign at the membrane placenta interface.
The characteristic bidirectional pattern of flow in arterio-arterial anastomosis is characteristic of monochorionic pregnancy.
DNA determination of zygosity by amniocentesis is an invasive method of determining the chorionicity, but is associated with risks of miscarriage.

B) There is an increased risk of congenital malformation, particularly congenital cardiac malformations and the risk of conjoined twins.
The risk of sudden intrauterine fetal death is more than in DCDA after 14 weeks and the management of the co-twin is difficult and requires management at a tertiary centre as well as the management of chromosomal abnormalities and prenatal invasive testing.
Twin to twin transfusion syndrome is specific to monochorionic pregnancies, caused by the imbalance of placental vascular anastomosis and characterized by the discordant growth and amniotic fluid volume. Severe cases can be detrimental to both fetuses.
Twin reversed arterial perfusion sequence is again specific to monochorionic pregnancies, characterized by the reversed flow of blood in the umbilical artery of one of the twins causing non development of the upper segment of the body – acardiac twin.
Cord entanglement is specific to MCMA pregnancy and chronic cord entanglement is present in almost all twins and can cause sudden intrauterine fetal death of one or both twins.

C) Initial USS needs to be done between 11-14 weeks to confirm viability, gestation, nuchal transluscency and to rule out major congenital abnormalities such as conjoined twins, neural tube defects.
Two weekly ultrasound scans to include measurements of AC, HC (and fetal brains), maximum vertical pool depth and umbilical artery dopplers(from 24 weeks) need to be organized from 16 weeks till delivery to recognize complications such as TTTS and growth discordance.
An anomaly scan with extended views of the fetal heart at 21 weeks as there is an increased risk of congenital cardiac abnormalities and a fetal echocardiography if there is any evidence of TTTS.
More frequent scans may be required to assess the fetal brains, growth and fluid volume in the presence of complications such as IUFD of one twin, following laser ablation of TTTS.

D) The management depends on the severity of TTTS and the maternal views towards the pregnancy.
Selective feticide by electocautery of the umbilical cord is an option if severe hydrops in the recipient twin or any evidence of brain damage in either of the twins. This can have an effect on the surviving co twin and needs regular monitoring. Fetoscopic laser ablation of the placental anastomosis is found to be safe and effective but needs to be undertaken in a regional fetal medicine centre. There is a risk of recurrence of TTTS if some of the anastomoses are missed during the laser ablation and needs frequent monitoring by ultrasound scans.
Other procedures such as amnioreduction and septostomy may not be as effective as laser ablation as the source of TTTS is not treated.
Termination of pregnancy is an option if the parents do not wish to continue the pregnancy.
Posted by R S.
R S

a. Chorionicity is determined by ultrasound examination, preferably before 10-11 weeks of gestation with a photograph kept with the patient records. Presence of single placental mass indicate monochorionic placenta (MC) while in dichorionic placentas (DC) we can see two separate placentas. Moreover, a T-sign is indicative of MC placenta while lambda-sign indicate dichorionic placenta.

b. MC twin pregnancy is at higher risk of perinatal morbidity and mortality in comparison with DC twin pregnancy. There is higher incidence of complications that are unique to MC twin such as TTTs, discordant fetal growth or twin reverse arterial perfusion (TRAP). As a result, these will lead to higher antenatal intervention, higher incidence of preterm labour and antenatal still birth. In addition, a woman with MC mono amniotic pregnancy is at risk of cord entanglement during vaginal delivery, therefore, elective caesarean section is recommended.

c. Detailed anomaly scan with extended views of fetal heart is recommended at 16-20 weeks to detect structural anomaly and congenital heart disease. From 20- 24 weeks gestation, it is recommended weekly for early detection and staging TTTS according to Quintero staging system which help early interference and management. From 24 weeks till term, US is done fortnightly to detect fetal growth potential and late onset TTTS.

d. The options are laser ablation of the communicating blood vessels; this will reduce transfusion between the two fetuses. In some cases it needs to be repeated for complete separation of anatomizing blood vessels.

Other option includes septostomy between the two amniotic cavities, it will allow shifting amniotic fluid from the polyhydramnious sac into the oligohydramnious sac, it can reduce pulmonary hypoplasia in the donor fetus.

Amnioreduction of the polyhydramnic sac can reduce maternal discomfort and prolong pregnancy; it needs to be repeated as fluid re-accumulate.

Selective fetal reduction by cord occlusion using bipolar diathermy is also recommended management option. In addition to termination of pregnancy which is done after full maternal counseling.
Posted by Green K.


Green:

a) Ultrasound presence of lamda sign at the placenta-membrane interface indicates dichorionocity. Ultrasound presence of \"T-sign\" at the placenta -membrane interface indicates monochorionicity. Chorionicity best established before 14 weeks gestation. If unsure of chronicity during scan, a photographic record of the placenta-membrane interface would be obtained and patient referred for specialist scan. Ultrasound assessment of chronicity is accurate but not 100% sensitive.

b) Higher fetal loss rate especially second trimester loss before 24 weeks. Higher risk of neurodevelopment morbidity. Monochorionic monoamniotic pregnancy (1% of twins) would have high risk of cord entanglement. Increased risk of complications of vascular placental anastomoses such as twin-twin transfusion syndrome(TTTS)

c) She would require an ultrasound scan between 10 to 13 weeks gestation to assess viability, chronicity and major congenital malformation. This is because chronicity is best established before 14 weeks for accuracy. Presence of major congenital malformation would enable counseling and early discussion with the patient regarding early termination of pregnancy. Nuchal translucency test can be done then if patient wishes screening for fetal aneuploidy.
Fetal ultrasound assessment every 2 to 3 weeks from 16 weeks onwards. Scans between 16 weeks to 24 weeks are aimed to detect first occurrence of TTTS. Scans done 24 weeks onwards are aimed to detect concordant or discordant fetal growth restrictions.
A detailed ultrasound scan with extended views of the fetal heart would be done at 18 to 20 weeks. This is to detect presence of major cardiac abnormalities which has an incidence of 0.5% of monochorionic pregnancies.
Ultrasound scans at between 32 and 34 weeks would be also to determine presentation of the first twin. This to enable the presentation of the first twin to be taken into consideration during the discussion with the patient regarding the mode of delivery at 36 to 37 weeks.

d) Management would be in conjunction with regional fetal medicine with support of specialist expertise. Laser ablation of the anastomotic placental vessels rather than by amnioreduction or septostomy. Termination of pregnancy in severe TTTS. Selective termination using bipolar diathermy in cases with severe hydrops in recipient twin or presence of ultrasound evidence of cerebral damage in either twin. Patient would need to understand her clinical condition and her options and would be provided written info.

Posted by Seham S.
SE-SA

(a) Chorionicity and amniocity would be established by u/s at 10-13 week.Chorionicity determination is almost 100% accurate in 1st trimester and 80-90% in 2nd trimester . Dichorionic twins have thick chorionic inter-twin septum which is lambda sign which disappear at 20 week .Monochorionic twins is diagnosed by T sign.Presence of one or two sacs should be also confirmed as cord entanglment is increased in monoamniotic twins.Risk of vanishing twin if u/s diagnosis is made early in pregnancy.

(b) Monochorionic twins is associated with increase risk of twin to twin transfusion syndrome (TTTS) .15% of MC twin is complicated by TTTS .It is intrauterin growth restriction and oligohydramnios in doner twin ,polyhydramnios and cardiomegaly in recepient twin. If untreated it has perinatal mortality of 80%. Doner twin is at high risk. Increase risk of neurological impairment in survivors to 20% .Recepient twin may have hypertention,cardiomegaly and renal failure. Monochoionic,monoamniotic twins may have increase risk of cord entanglment.

(c) Booking u/s at 10-13 week to detrmine chorionicity,amniocity,gestational age and viabilty . Nuchal tranclucecy should be offered to patient who requir down screening.It has similar sensitivity to singletone pregnancy ,however it has false positive results in twin pregnancy . Serum screening for down is not accurate in twin pregnancy. Anomaly scan at 18-20 week should be done for detection of congenital anomalies . Incidence is increased in twin pregnancy.Serial growth scan should be done every 2 weeks from 16 w for early detection of TTTS . Early diagnosis can help in managment including referral to fetal medicine center and reduce perinatal mortality.Dppler u/s and BBP may be used especialy if death of one twin occured and there is need to follow up the surviving twin. Middle cerebral artery doppler is used to diagnose anaemia in living twin. Also in case of managment of TTTS ,u/s with doppler is used for post treatment follow up.

(d) Managment options include amnioreduction which improve polyhydramnios and reduce preterm labour ,however it is associated with infection, premature rupture of membrane and need for repeated procedure every 3-4 weeks. Septostomy is another option through inducing a hole in the membrane between twins using needle or laser so, equilibration of amniotic fluid in the 2 sacs take place.Laser ablation through photocoagulation of vascular anastomosis could also be done at that age. Selective fetecide through cord occlusion could be done using bipolar diathermy especialy in grade iii/iv TTTS or as alternative to laser ablation. No treatment and termination of pregnancy might be offerd to all patients.
Posted by Bee N.
Bee

A healthy 34 year old woman underwent in-vitro fertilisation for unexplained sub-fertility and two embryos were replaced. She is found to have a twin pregnancy at 6 weeks gestation. (a) Discuss how you would establish chorionicity [5 marks]. (b) Discuss the additional risks associated with monochorionic twin pregnancies when compared to dichorionic twin pregnancies [5 marks]. (c) She is found to have a monochorionic twin pregnancy. Discuss and justify your schedule of ultrasound assessment of the fetuses [6 marks]. (d) What are the options for managing twin to twin transfusion syndrome presenting at 20 weeks gestation? [4 marks].

A)To establish chorionicity, I will do an ultrasound scan as soon as possible. The lamda sign suggests monchorionic while the T sign suggest dichorionic twins. Scan for chorionicity is more accurate in 1st trimester (11-14 weeks) and less so in 2nd trimester. The Lamda sign usually disappears after 20 weeks gestation. The gender of the implanted embryo coild be checked by amniocentesis at 15 weeks or CVS. If of different gender, then it definitely will be dizygotic and therefore dichorionic.

B)Monochorionis twin pregnancies are more prone in first trimester to miscarriages. The chance of vanishing twin higher with monochorionic twin pregnancies. In the first trimester during the dating scan at 11- 14weeks, we also look for gross structural/congenital anomalies which are higher with monochorionic pregnancies compared to dichorionic pregnancies.
They are more likely to have the Twin twin transfusion syndrome which are more likely seen before the 24th week of pregnancy and occurs in about 10% of monochorionic twins. The Twin reversed arterial perfusion syndrome occurs in 1% of monochorionic twins and involves an \"acardiac\" parasitic twin and a \"pump\" host twin. There is also more likely of fetal death with monochorionic prenancies for the reasons mentioned above. The fetal mortality and morbidity (neurological damage) are found more with monochorionic pregnancies.

C)My Ultrasound schedule will inlcude a first trimester scan for chorionicity. This should be done as soon as possible. Dating scan is organised for 11-14 weeks. In this scan I would also try to confirm viability of both twin and look out for gross structural abnormality. If she chooses to have her fetuses screened for Downs syndrome, I will organise nuchal trasluscency scan at approximately 12 weeks gestation. This will guide the need for ultrasound guided amniocentesis at 15 weeks. The usual blood test for singleton pregnancies are unreliable for multiple gestation. At 16 weeks I will start 2 weekly ultra sound scan to look for sign of TTTS. I will be looking at the growth of the twins, liquor volume, bladder for presence of fluid, fetal heart beat. The risk of this is significant up to 24 weeks gestation. An anomaly scan and cardiac scan will be done at 20 and 24 weeks respectively due to thier increased chance of these problems. I will commence ultrasound scan at 24 weeks specifically for growth which will include abdominal circumference, liquor volome measurement and umbilical artery doppler for end diastolic flow. This will be done every 2 weeks but frequency may be increased if abnormalities are found and closer monitoring needed. I will check for specifically for placental site and presentation from 28 weeks gestation everytime she come for a growth scan.

D) TTTS ashould be managed in a fetal medicine unit by specialists in fetal medicine. The options will depend on severity on TTTS and include to do nothing and observe nature take its course. There is also room for laser ablation of artero- venous communication. Amnio reduction is acceptable though not as effective. Septotomy for diamniotic twins whereby a hole is made in the membrane dividing both amniotic cavities has been shown to be effective. Selective fetocide by occlusion of umbilical cord of the twin least likely to survive will help prevent peri mortem transfusion and demise of the surviving twin if it was otherwise left to die naturally. Pregnancy can also be terminated if the mother so wishes.
Posted by Bgk H.
a. I will perform a pelvic scan to demonstrate present of Lambda sign at placenta-membrane interface that indicate dichorionicity and presence of T sign indicate of monochorionicty. At later gestation, I will determine the number of placenta from ultrasound scan. And following delivery determine the number of placenta after expulsion of the placenta.

b. Generally there is increase morbidity and mortality of monochorionic twin. There is increase risk of Twin to Twin Transfusion Syndrome. If it developed there is increase risk of intervention and may lead of complication like repeated procedure, infection, failure of the procedure, pain morbidity and miscarriage. Patient may also have higher risk of psychological morbidity. In monochorionic pregnancy, there is also increase risk of single intrauterine fetal death, and when this happen there is increase risk of the surviving twin to be affected and die to compare with dichorionic twin. Monitoring will be difficult. Monochorionic twin also associated with monoamniocity and will have higher risk of cord entanglement.

c. I will arrange a scan between 11wk-14wk to be able to determine the viability of the pregnancy and the chorionicity as performing later than that will affect its accuracy. At the same setting I would like to perform Nuchal Translucency measurement for screening as there is increase risk of twin pregnancy to develop congenital anomalies. This is important that maternal serum screening is not reliable in twin pregnancy. I will arrange an anomaly scan at about 20weeks of gestation to detect any structural abnormalities including the heart echocardiogram as there increase risk of fetal anomaly detected at this gestation especially in twin pregnancy. And if there no concern, I will arrange 2 weekly scan from 26 weeks onward s as to detect the development of TTTS by measuring the depth of amniotic pool, bladder and the features of both twin. If the fetus(es) is detected abnormalities such as TTTS and has undergo procedure, more frequent scan warranted to monitor the success of the procedure, complication and recurring symptoms. I will arrange another scan at about delivery to determine the leading twin presentation to decide the mode of the delivery as there is difficult to assess clinically.

d. I will explain to the mother in sensitive manner and tell her that there is not because what she do or don’t do to develop this condition. I will refer to the fetomaternal centre and need further scan evaluation of and stage the condition using Quintro Staging and further counsel the patient regarding the prognosis accordingly. If good prognosis the options are to continue the pregnancy but she must be aware that the need of further intervention and its associated complication. The interventions include amnioreduction but it may need repeated procedure. The other option is sepstostomy which may reduce the number of repeated procedure but the outcome is the same. If there is expertise in utero laser ablation to further prevent abnormal blood flow direction that may worsen the condition. Other option is termination of pregnancy.
Posted by Gowrishankar S.
a) Chorionicity can be well established by offering an ultrasound scan at 10 -13 weeks of gestation. Ultrasound diagnosis was based on demonstration of the “lambda” or twin peak sign in dichorionic and “T sign “ in monochorionic pregnancy at the placenta-membrane interface. The finding of two placentae or discordant gender of the foetuses confirms dichorionic pregnancy.The identification of an arterial-arterial anastomosis by colour Doppler insonation of the chorionic plate may cofirm monochorionicity. If difficult to confirm the chorionicity patient may have to be referred to specialist before 14 weeks. In difficult cases zygosity studies may have to be performed.
b) The additional risks associated with monochorionic pregnancies are TTTS in 15% of monochorionic pregnancies, discordant malformations, cord entanglement in monochorionic monoamniotic pregnancies , Twin reversed artery perfusion sequences (TRAP), single fetal death and increased incidence of IUGR(intrauterine growth retardation) compared to dichorionic pregnancies.

c) A nuchal translucency should be done at the same time as chorionicity to exclude aneuploidies. All monochorionic twins should have a detailed ultrasound scan which includes extended view of the fetal heart . Fetal ultrasound assessment should take place every 2-3 weeks in uncomplicated monochorionic pregnancies from 16 weeks. Ultrasound examination from 16 -24 weeks to identify TTTS(Twin to twin transfusion syndrome). After 24 weeks the main purpose is to detect fetal growth restriction.

d) The options for management of TTTS at 20 weeks are laser ablation, amnioreduction, and septostomy. Selective termination of pregnancy using bipolar diathermy of one of the cords and termination of the pregnancy. Severe TTTS at this pregnancy is preferably treated with laser ablation than amnioreduction or septostomy. The management should take place in a tertiary referral center by a feto maternal spcialist. Counselling and support should be offered to the patients.
Posted by Dr Dyslexia V.
X

a) I would establish chorionicity based on ultrasound which preferably a trance vaginal ultrasound to assess placenta and its membrane. The presence of lambda sign would indicate interposition of 2 thickened placental edge establishing 2 separate placenta (dichrorionicity) DC. While the presence of T sign shows thin membrane arising from a single placenta showing monochorionicity (MC). Further follow up and determination of a discordant sex would be beneficial to diagnose DC. Or a further postpartum study of the placenta after the delivery of the fetus would establish the diagnosis by assessing vascular anastomosis by dye injection.

b) MC twin pregnancy has increased risk due to unidirectional vascular anastomosis between the 2 twins which could lead to the risk of twin to twin transfusion syndrome (TTTS) which occurs in 13% of MC twins. It involves a donor twin which will suffer from severe intrauterine growth retardation or even death when it shuns vascular supply to the recipient twin which would suffer from severe cardiac overload which could lead to hydrops of the recipient twin. Other risk include cord entanglement and accidents which could cause intrauterine death in the monoamniotic twin variant. There is also increase in aneuploidy in MC twins. Heart structural anomaly is also increased in MC twins. Other risks also include the rarer entities such as TRAP(Twin Reversal Arterial Perfusion Syndrome) with presence of a acardiac twin. There is also higher risk of neuro developmental delay and rate of still birth in MC twins.

c) A regular ultrasound by a fetal maternal medicine specialist of consultant will be done as it is a high risk pregnancy. An ultrasound should be done at 12 weeks to assess NT measurement for screening of aneuploidy and subsequent scan for determination of chorionicity. A 2-3 weekly scan to assess any growth discrepancy or miscarriages as the risk of TTTS is highest at gestation less than 24 weeks. A fetal anomaly scan should be done at 18 weeks for any major structural abnormalities. A further fetal echo cardiography could be done at 22 weeks as MC twins are associated with increased risk of structural heart abnormalities. Subsequently she should be followed up 2-3 weeks for growth presentation and plasentation till delivery.

d) This condition should be managed by a tertiary referral centre with fetal maternal expertise. The options include amnio reduction which involves removal of the amniotic fluid from the recipient twin but this procedure has to be repeated periodically. Other option include septostomy which involves the creation of a whole in the separating membrane which does not require repeat procedures. The most promising modality is laser vascular ablation which found to be almost curative for TTTS. It involves ablation of unidirectional vascular anastomosis to create a balanced vascular anastomosis. But occasionally it could cause reversal of the flow. Other options include selective feticide which could be done for an unhealthy fetus or hydrops by cord occlusion or cord diathermy. COunselling and written information should be given for this patients.
Posted by tahira jabeen J.
tj
a)
as guided by RCOG guideline all twin pregnancies should have scan at 10-13 weeks for dectection of chorionicity.it has sensitivity of >80% specificity of >90%.T sign on uss means monochorionic twins but lamda suggests dichorionic twins.
iter twin membrane thickness ca also help as if less tha 2 cm can be monochorionic pregancy,but its not proved by evidence.
if late gestation fetal sex ca also help as different sex of twins will role out monochorionic twins but around 30-40% dichorionic twins ca be of same sex.
b)
risks of prematurity,aneuploidy,miscarriage ,perinatal mortality will be 2 folds increased as compared to dichorionic pregnancy.
other specific risks associated with moochorionicity are TTTs
which effects about 15% monochorionic pregancies.in it due to same placenta & arteriovenous anastomosis one twin becomes donor & other reciepient.one will be oligo and other polyhydramnios insevere cases will lead todiscordant growth of both twins, hydrops & fetal demise.
other risk ca be trap which ca n affect 1% preg inthis one twin is acardiac & other twin heart is working for acardiac twin.other risk is the complicated situation of one fetus demise as it may cause neurilogical deficit in surviving twin.if this happens i early preg can lead to more more demage needs MRI brain of survivg twin.
c)
as advised by RCOG guideline fetal uss assessment should take place every 2-3 weeks in uncomplicated monochorionic pregnacies from 16 weeksas TTTs does not occur before 16 weeks..uss survilliace should include abdominal circumferance,fetal brain imaging,AFI,umblical artery doppler.also all monochorionic twins should have detailed cardiac scan.a fetal echo should be done in case of TTTs.
d)the management should be done in fetal medicine unit with expertise in this speciality.
the options foe managing TTTs are
amnioreduction,septostomy,laser ablation.
mild cases can be treated with amnioreduction,but it may need to have repeated sessions.septostomy can be done in mild case.s.
but severe cases & case below 26 weeks should be treated by laser ablation.survival rate is better with laser treatment.
some patient may request forselective termiation of preg
in case of severe TTTs,by bipolar diathermy.this mAY BE appropriate in hydrops fetalis in reciepnt or cerebral demage in either twin.
Posted by Im F.
A
To establish chorionicity patient must be between 10 wks to 14 wks of gestation.an ultrasound scan should be done to look for lambda or T sign at the membrane placenta interface.T sign represents monochorionic and lambda represents dichorionic.phtograph should be talken and kept in the records.if not sure she should be refered to fetal medicine unit for confirmation before 14 wks of gestation.the sensitivity and specificity for diagnosing chorionicity by scan is high between 10-14 wks after which it reduces.

B
monochorionic twins are at greater risk of premature delivery,fetal growth retardation than dichorionic twins . there is also higher incidence of twin to twin transfusion syndrome and discordant growth in MC twins Death of one twin due to TTTS can result in interfetal transfusion and the surviving twin develops hypoxic injury to vital tissues notably to brain.

C
the ultrasound sans are done every 2- 3 wks starting from 16 wks onwards in an uncomplicated monochorionic twin. incase of TTTS intensive monitoring of the twins is requiredwith more frequent scans. detail scan should be done and fetal heart should be checked for abnormalities.echocardiography should be done for severe cases of twin to twin transfusin.

D
after councilling parents can be offered no treatment option or termination of pregnany.
serial amnioreduction and septostomy have similar results.laser ablation ot the anastamosis has more live bithe with lesss neurologial sequlea and reduction in number of fewer neonatal and perinatal deaths.long term outcomes and the effect on mother is not known.selcetive feticide by laser coaglation of cord can be offered .all these procedures should be done in the tertiary centre under fetal medicine specialist.
written information should be provided and documentation of the discussion should be done.

im
Posted by Shamita S.
ANS
(A) Chorionicity is mainly established by USS examination ,which should be performed by an expert trained in doing so. It should be ideally performed before 14 wks as it is difficult to study the dividing membrane after that.The dividing membrane intersecting the placenta to be looked for as lambda sign would indicate a dichorionic twin whereas an invert T sign would sggest monochorionicity.The thickness of the membrane and the number of layers should also be looked for as a 4 layered dividing membrane would be in dichorionic gestation.Discordant foetal sex is suggestive of dichorionic twin .A concordant sex could be monochorionic or dichorionic .A single placental mass would be suggestive of monochorionicity..The photograph of the uss findings to be kept as a record and for further analysis by expert if in doubt.Should the chorionicity be still in doubt USS to be performed by a specialist before 14 wks .A USS is not 100%sensitive .If there is still doubt confirmation by DNA analysis to b econsidred.
(B) Monochorionic pregnancies are associated with higher foetal loss rate (even less than 24wks),the mean birthweight and mean gestational age at delivery is less than in dichrorionic twin .
The perinatal mortality is also higher .Cord entanglement causing foetal hypoxia and foetal death is evident in monochorionic monoamniotic pregnancies.Conjoined twins are also seen in monoamniotic sacs leading to increased perinatal morbodity and mortality.Monochorionic placentas are associated with vascular anastomosis leading to Twin twin transfusion syndrome and TRAP syndrome which also increases perinatal mortality and morbidity.There is also increase in neurodevelopment delay in surviving twins in monochorionic gestations.
(C) Nuchal translucency be offered at 10-13 wks gestation for screening of anueploidy, as serum screening would not be accurate .The major concren in monochorionc gestation is detection of TTTS as it is a major cause of IUFD ,and it occurs before 24wks,so USS should be done once in two wks from 12 wks till 23wks by a person well versed in detecting the uss changes. TTTS and increased perinatal death can also predicted by discordance in NT and CRL measurements by>10%.
A detailed anamoly scan should be scheduled at 19 wks to look for structural malformations and soft markers as monochorionic twin is associated with increased congenital malformations .For the same reason a foetal echocardiography should be performed at 21 wks by a specialist .
After 24wks USS should be done every 2-3 wks for foetal growth assessment ,to look for concordant or discordant IUGR
(D) A TTTS should be managed in concordance with referral foetal medicine centre and a specialist expert .The management would depend on then grade of TTTS.
A supportive management can be offered for grade 1 ,but the patient would require close follw up by uss as the progression to severity cannot be predicted .
Laser ablation is a good option for severe TTTS diagnosed before 24wks as it results in more live babies without neurological abnormalities .The drawback is that there is a chance of recurrance if the anastomosis is missed .
Septostomy done by creating a hole in the dividing septum with the intention of improving amniotic fluid volume in the donor sac ,and amnioreduction is another op[tion but no significant difference is observed in the outcome by these methods.
Some would prefer selective foetal reduction by diathermy of the cord ,for the recepient twin with sever hydrops .
There is also an option of termination of pregnacy if the couple wishes so or it the twin is found to have anomalies not compatible with life.
These pregnancies should be followed by wkly USS and consider delivery by 34wks at a tertiary centre.
Posted by Jan I.
JAN

A)Chorionicity can be best established by ultrasound (USS) at 11 weeks gestation. At this stage accuracy for determining chorionicty is 90-100%. Dichorionic (DC) twin pregnancies will characteristically have a lambda’ or ‘twin peak’ sign caused by the inter-pregnancy membrane. Monochorionic (MC) pregnancies will have a ‘T sign’ at the membrane-placenta interface. Chorionicity can also be established at the anomaly scan, though accuracy is less than in the first trimester. DC twins will demonstrate separate placentas and can be of different sexes. MC will have a single placenta and anastomoses may be demonstrable on colour flow doppler. The presence of a single sac (monoamniotic) is also indicative of a MC twin pregnancy.

B)MC twin pregnancies are subject to greater risks than DC twin pregnancies. As the fetuses share a placenta there is a 15% chance of development of the twin-twin transfusion syndrome (TTTS) which arises as a result of unidirectional arterio-venous anastomoses therein. The donor twin will become growth restricted with oligohydramnios and the recipient twin may become plethoric and hydropic with polyhydramnios evident. TTTS carries significant risk of mortality to both twins if untreated. There is also possibility of development of the twin reversed arterial perfusion (TRAP) sequence where one twin provides circulatory support for itself as well as its acardiac co-twin. The acardiac twin has lethal abnormalities not compatible with life and the pump twin is at risk of cardiac failure and subsequent demise. MC monoamniotic twins share a sac and therefore a risk of cord entanglement and cord accidents that can lead to fetal demise. If there is demise of one twin, regardless of cause, then this carries a risk of death to the remaining twin because of the shared circulation. Overall there is an increased risk of fetal loss. There is also an increased risk of developing pre-eclampsia in MC pregnancies over DC pregnancies.

C)A nuchal translucency should be performed at 12 weeks as this is the only accurate means of aneuploidy screening as serum screening is inaccurate. MC twins should then have fortnightly USS from 16 weeks onward. This should be undertaken to monitor for signs of growth restriction, discordant growth & TTTS all of which are more common in MC twin pregnancies. The scan should include measurement of growth parameters particularly abdominal circumference, head circumference and liquor volume. A detailed cardiac scan should be performed at the 20 week anomaly scan. Fetal echocardiography at a tertiary referral centre may be warranted if any abnormalities are found. After 24 weeks umbilical artery doppler and middle cerebral artery doppler assessments of both fetuses should also be performed to look for any placental insufficiency and evidence of subsequent redistribution. If there is evidence of abnormality on umbilical artery dopplers then the frequency of scanning can be increased to weekly, or more frequently, if necessary. Flow through the ductus venosus can also be measured in these circumstances to guide plans for delivery in suspected evolving placental failure. These serial scans will also be checking for evidence of TTTS. These include a discrepancy in growth between the 2 twins with evidence of oligohydramnios in one twin and polyhydramnios in the other twin. The presence of ascites, pleural effusions, pericardial effusions and state of the fetal bladder will also be noted in order to class the severity of TTTS.

D)If TTTS is diagnosed then referral should be made a tertiary referral centre for management. Initial management would involve close observation with USS and classification of the severity of TTTS to guide the need for intervention. Laser ablation of placental anastomoses can be undertaken to treat TTTS by functionally separating the fetal circulations and has been shown to increase survival in both twins. There is no value in septostomy or amnioreduction as these provide no survival benefit. Steroids should be administered in anticipation of delivery if premature delivery is necessary. This should be coordinated with neonatologists to confirm adequate provision of care for the babies. In severe cases selective termination can be discussed to spare one twin though this still will carry a risk to it.
Posted by G. K.
GSK
A)
Chorionicity is best confirmed by ultrasound in fetal medicine unit under supervision of a fetomaternal consultant. The presence of a thick tongue of membrane at the placenta membrane interface(Lambda sign) is highly suggestive of a Dichorionic pregnancy. The presence of a thin membrane (T sign )is suggestive of monochorionic diamniotic pregnancy(MCDA). Absence of dividing membrane between the two fetuses is suggestive of monochorionic monoamniotic (MCMA) pregnancy. If there\'s any doubt, a second opinion should be sought.
B)
The addiitonal risks associated with MC when compared to DC pregnancy include increased incidence of perinatal morbidity and mortality, increased incidence of fetal loss before 24 weeks, increased risk of congenital anomalies such as anancephaly and structural heart defects and preterm labour.Also the risk of twin to twin transfusion syndrome is exclusive to MCDA and MCMA pregnancies which leads to growth disconcordance and increased risk of morbidity and mortality in one or both twins.Also there\'s very high risk of cord entanglement in MCMA. This risk is nonexistent in DCDA pregnancies.
C)
Ultrasound assessment is done at 11-13 weeks for nuchal translucy to screen for aneoploidy. Serum screening has a poor detection rate in twins.Also if there\'s more than 10% disconcordance between CRL and NT, such a pregnancy may be at increased risk of TTTS. At 19 weeks anomaly scan is carried out since ther\'s increased incidence of congenital anomalies. A detailed scan is done at 21 weeks to specifically look for structural heart defects and outfow tracts since the incidence of these is raised in MC pregnancies. A cervical length scan is carrid out at 23 weeks to determine the risk of preterm labour. If cervical length is less than 25mm at 23 weeks, then the \'s 80% chance of going into preterm labour before 30 weeks. The use of prophylactic cervical suture and corticosteroids remain uncertain.
From 16 weeks and onwards i.e until 24 week, regular lutrasound is done every 2 weeks to detect TTTS, since this condition affects 10-15% of MCDA pregnancies.After 24 weeks fortnightly U/S is done to rule out IUGR and growth disconcordance which is not secondary to TTTS.
C)
The treatment options for treating TTTS after 20weeks include laser ablation of arteriovenous anastomoses leading to TTTS. After this procedure the recurrence risk is 14%.Rarerly reversal of the condition can occur with donor twin becoming the recipient twin and vice versa. Other option include Septostomy which aims to equilibrate amniotic fluid across the dividing membrane.Other option include serial amnioreduction . In case of a compromised fetus, complete coagulation of umbilical vessels is carried out before selective fetocide so as to prevent damage to the surviving twin.
Posted by Nadira N.
A) Chorionicity can be easily determined by first trimester ultrasound scan in a non tertiary center.The interface of chorionic membrane at the site of attachment at chorion is inspected which shows lambda sign in dichorionic twins due to a triangular piece of chorion in between the membranes .The attachment of membrane in monochorionic twins is T shaped and it is thin as compared to dichorionic twins. The lambda sign disappear after 20 wks .Thereafter two placentas seen lying separately or dischordant sex suggest dichorionicty.If both fetuses are of the same sex and and both placentas are seen fused the chorionity can be determined by colour doppler insonation of the chorionic plate.Presence of an arterial arterial anastomosis suggest monochorionic prgnancy. Amniocentesis in fetal medicine specialist unit can also be used in diagnosing chorionicity in certain situations such as finding an abnormality in one twin.
B) Almost all monochorionic twins have vascular anastomosis between placental vessels.These have been implicated in the developmnet of twin to twin transfusion syndrome in 15% of monochorionic twin pregnancies.From 2nd trimestor onwards fortnightly ultrasound is necessary to make the diagnosis.If TTTS develops the donar develop hypovolaemeia ,growth restriction and oligohydramnios and abnormal umblical artery dopplers.The recepiant shows sign of overload with plyhydramnios cardiomegali and abnormal venous dopplers for e.g reverse flow in in the ductus venosus.In 1% of twins due to arterio arterial anastomosis twin reverse arterial perfusion(TRAP) develop .It is characterised by an acardiac twin which recieves its blood supply from a normal co twin .The perinatal mortality of the pump twin is considerable. The death of a co twin in monochorionic pregnancy is associated with an increased risk of death or severe neurological impairment in co twin due to transfusion from the surviving twin in the placental bed of dead twin and development of severe hypotensin in surviving twin .
C) Ultrasound assessment should be fortnightly in tertiary center between 15 and 25 weeks to make the diagnosis and staging of TTTS.Colour doppler ultrasound imaging can be used to detect superficial areterio arterial (AAAs) and veno venous(VVAs) anastomosis.The absence of AAAs is associated with increased risk of development of TTTS 61% versus 15%.Once the TTTS develops the severity is assessed by quitero staging system.Overall survival depend upon the stage at presetaion survival at stage 1 and 2 in the presence of AAAs is 100% ,at stage 3 the survival is 80% and stage 4 it declines to 50%.In the absence of AAAs the survival at stage 1 and 2 is 60% ,at stage 3 44% and at stage 4 it is 25%.At 20 to 22 weeks detailed scan for anatomy is required .Monochorionc twins are at increased risk of cardiac malformaton therefore fetal echocardiography will also be needed.From 25 weeks onwards in the absence of TTTS serial growth scan every 2 to 3 weeks will be required to assess the development of growth restrction.
D) If TTTS is left untreated the perinatal mortality rate exceeds 80%,with the donar at high risk of death than the recipiant.The management options are amnioreduction, septostomy,laser ablation and occlusive feticide.The option of non intervention and termination of pregnancy due to poor prognosis at this early gestation should also be offered.Once diagnosis of TTTS is made the women should be scanned weekly to look for worsening of the condition and timely intervention.For stage 1 and 2 amnioreduction can improve outcome by reducing preterm delivery secondary to polyhydramnios.It is indicated when AFI is more than 40.It does not treat underlying TTTS and there is risk of premature rupture of membranes abruption and chorioamninitis due to procedure itself.Septostomy allows excess fluid to pass from recipiant to donar where it can be swallowed or absorbed.Repeat procedures are not required like amnioreduction.For those with stage 3 and 4 laser ablation of anastomotic vessels with amnioreduction should be offered.Following treatment the women should be followed twice weekly with full doppler assessmnet initially and then weekly through out the pregnancy.If procedure is performed after 24 wks sterooids are administered before the procedure ,otherwise steroids are given prior to delivery.Timing of dellivery depend upon the the treatment.If repeated amniodrainage is required the delivery should be at 32 to 34 weeks of gestation.If laser treatment has been selected the optimal time for delivery should be at 34 weeks of gestation
Posted by shmaila S.
Dr SAS

(a) this women should be offered ultrasound at 10-13 weeks as chorionicity is best established before 14 weeks of pregnancy.on scanning lamda or twin peak sign indicates dichorionic and T sign indicates monochorionic twin pregnancy.photographic evidence of chorionicityshould be obtained.if any doubts about chorionicity than immediate senior opinion should be sought. if needed referal to a specialist unit should be made before 14 weeks of gestation.

(b) monochorionic twin pregnancy are at risk of second trimester miscarriage, preterm delivery,preeclampsia, twin to twin transfusion syndrome TTTS,discordant growth of the twins,fetal hydrops in cases of severe TTTS, fetal demise of one twin and neurological morbidity of the surviving twin, twin reverse arrterial perfusion(TRAP).in monochorionic monoamniotic twin pregnancy cord entanglement is a risk and may require early delivery.

(c) scan should be arranged at 10-13 week of pregnancy to establish chorionicity, viability, major congenital malformations and nuchal translucency. women who wish fetal aneuploidy screening should be offered nuchal translucency measurement.serial scans should be arranged every 2-3 weeks from 16 weeks. upto 24 weeks scan are to detect TTTS and after 24weeks mainly to detect fetal growth restriction.if TTTS is suspected then weekly scans to monitor fetal growth ( mainly through abdominal circumference, brain size, max depth of amniotic fluid, umbilical artery doppler studies) should be arranged

(d) TTTS should be managed in a regional fetal medicine unit where specialist care is available.TTTS is best treated with laser ablation before 26 weeks of gestation rather than amnioreduction or septostomy.pregnancies treated with laser showed 15% better survival in trials. if severe TTTS than termination of pregnancy can be offered as an option. selective termination of pregnancy can also be offered using bipolar diatthermy of cord if thereis evidence of hydrops fetalis or cerebral damage.

Posted by Preethi A.
(a)Ultrasound at 10-12 weeks is accurate in diagnosing chorionicity by the presence of either the ‘T’ sign (monochorionic )or the lamda sign(dichorionic). Establishing chorionicity helps to plan the Antenatal care as well as the timing and mode of delivery.
Different sexes in the fetus signifies dichorionic twins and can be identified in early scan .
Presence of two placentae also point towards dichorionic twins.

(b)Monochorionic (MC) twins have an increased risk of Perinatal mortatilty and morbidity compared to Dichorionic(DC) twins. Twin to twin transfusion syndrome(TTTS) and Twin revere artetial perfusion (TRAP) are more common in MC than in DC twins.
Single fetal loss and miscarriage are higher in MC twins. Cord entangelement is seen in MCMA twins and prematurity both iatrogenic and spontaneous is more common in MC twins.

(c) Anuploidy is best determined by nuchal translucency as the markers are raised and hence unreliable in twin pregnancies.
A detailed USS at 16 weeks with fetal echo to rule out any congenital abnormality need to be arranged.
Anomaly scan at 20-22 weeks for placental localisation.
Furthes USS at 2-3 weekly intervals to identify signs of TTTS by measuring the liquour volume and any sign od discordant growth or hydrops is also arranged.
After 24 weeks 2-3 weeks scan to assess growth as abdominal girth is unreliable and TTTS is unlikely to present for the first time after 24 weeks.
(d)Treatment options include lazer ablation of the A-V anastamosis ,which can either be selective with the help of dopplers or midline. Selective ablation has the advantage of preserving the A-A and V-V anastamosis which are supportive.
Septostomy helps in equalising the liquour volume but has the disadvantage of having to be repeated.
Amnioreduction can also help but need to be repeated.
Selective termination of the receipient twin by laser ablation of the cord or termination of both twins need to be discussed in a sensitive manner.
Support group and written information are also helpful
Posted by Dr Asia  K.
A.The best investigation to establish the chorionicity is ultrasound scan between 10 to 13 weeks.Monochorionicity can be demonstrated by finding the T sign at membrane -placenta interface .Dichorionicity can be confirmed by demonstrating the Lambda sign or the Twin peak sign.Different sx of the twins and different placentae can suggest the dichorionicity.Photographic evidence should be retained in the patients,s notes.If there is any doubt,second opinion should be sought out without any further delay.

B.Monochorionic twins are at a higher risk of perinatal morbidity & mortality compared to dichorionic twins .This is mainly due to second trimester loss.The risk of fetal death in MC pregnancies after 24 weeks is higher than DC pregnancies(4.9% versus2.8 % respectively).MC twins have greater risk of neurodevelopmental morbidity .The mean birth weight & gestational age at delivery is also less for MCT as compared to DCT.10-15% of monochorionic pregnancies can be complicated by twin to twin transfusion(TTTS) .This is more common in MC diamniotic geatation compared to MC monoamniotic gestation.This is more likely in pregnancies having an unidirectional placental artery-vein anastamosis.MC twins are at a higher risk of neuro developmental morbidity .Death of co-twin in MC twins may lead to heamodynamic changes in the surviving twin causing end organ damage especially the brain .MC twins are also at an increased risk of discordant abnormalities including twin reversed arterial perfusion sequence.Monoamniotic twins are at an increased risk of cord entanglement & higher risk of perinatal mortality & morbidity.
C.The woman is referred to fetal medicine specialist .The woman is offered an ultrasound examination (USG) between 11-14 weeks nuchal translucency(NT) for fetal aneuploidy screening.The role of NT screening in predicting TTTS is not clear.She is offered ultrasound scan every 2-3 weeks from 16 weeks gestation.Serial scans between 16-24 weeks gestation is aimed at detection of TTTS .The surveillance of uncomplicated MC twins should occur at interval of 2-3 weeks from 16 weeks and should include the maximum amniotic pool depth in each sac, abdominal circumference, brain imaging & umbilical artery doppler studies(after 24 weeks).Each cord should be studied seperately. Umbilical artery waveform in MC twins may show cyclical absent or reversed end diastolic velocities.These are more common in discordant growth restriction .This is done for early detection of TTTS.A detailed anomaly scan of both fetuses is done
at 20-22 weeks gestation with extended views of fetal heart . In the presence of TTTS fetal echocardiography may be offered to assess the severity.
USG is offered every 2-3 weeks or according to unit protocols after 24 weeks.This is for monitoring of fetal growth & well being .Although new onset TTTS is rare after 24 weeks,this is looked out for during each scan.
D.TTTS must be managed in a fetal medicine unit .Management depends upon the severity of TTTS, facilities available and maternal wishes.Severe TTTS can treated by laser ablation of anastomosis, amnioreduction or septostomy.Laser ablation is preferred since it results in lower incidence of perinatal mortality & morbidity & more surviving babies without neurological impairment when compared to amnioreduction.The option of termination of pregnancy is discussed if the woman wishes so. another option would be to offer selective termination if one twin is severely hydropic or shows evidence of brain damage.This would involve diathermy of the umbilical cord of the affected twin.Single fetal death in MC pregnancy should be referred and assessed in a regional fetal medicine centre.