Umbilical vein thrombosis as a possible cause of perinatal morbidity or mortality: report of two cases.

Significant occlusion of the lumen of the umbilical vein by thrombus was observed in 2 patients with unexplained intrauterine fetal death (IUFD)/fetal distress. Although a normal non-stress testing result was obtained 7 days prior to IUFD in one patient, IUFD was noted during regular antenatal care at 39 weeks of gestation; intrapartum abrupt onset of deceleration in fetal heart rate pattern was observed at 40 weeks of gestation, lasting 14 min until vacuum extractor-assisted delivery in the other patient. Umbilical vein thrombosis was considered contributory to IUFD and the abrupt deterioration in fetal heart rate pattern in these 2 patients. Histological examination of the umbilical cord is thus important in unexplained fetal death/fetal distress.