A healthy 37 year old woman presents 6 days after IVF and embryo replacement with abdominal pain and persistent vomiting. P = 110/min, BP = 123/78 mmHg, SPO2 = 97% on air and her chest is clear. There is marked abdominal distension with shifting dullness. Pelvic ultrasound scan identifies enlarged multi-cystic ovaries of 12.8 cm in maximum diameter with ascites. Chest X-ray is normal. Hb = 154 g/L with a haematocrit of 0.47. Na = 139 mM, K = 3.7 mM and renal function tests are normal. Urine out-put has been 35 ml in the first hour.