A 23-year-old woman was admitted to the obstetric ward at 37 weeks in her fourth pregnancy. She complained of colicky generalized abdominal pain and nausea for 6 h before her admission. The antenatal period had been uneventful. On examination the uterus was not tender, consistent with 37 weeks gestation, and a fetal heart beat was present. There was tenderness on palpation in the epigastrium and right hypochondrium, but there was no abdominal guarding and normal bowel sounds were present. Her pain settled but returned 48 h later with vomiting of bile-stained fluid. Biliary colic was diagnosed. A full blood count, plasma electrolytes and serum amylase were normal and a plain abdominal X-ray showed no abnormality. She was treated with intravenous fluids and again her symptoms quickly settled. Four days after admission an ultrasound examination was performed. This showed a normal gall bladder, liver and kidneys but also revealed an elliptical cystic mass extending from the renal angle into the right iliac fossa. The nature of the mass was uncertain but it was considered that it might be dilated loops of small bowel. The patient remained asymptomatic. A week after admission she developed a further recurrence of right sided upper abdominal pain and vomiting. At the time she also reported reduced fetal movements. Cardiototography showed diminished baseline variability and reduced fetal movements. Because of the abnormal fetal heart trace, labour was induced and 1 h later, at only