Prenatal diagnosis of umbilical artery thrombosis.

Umbilical artery thrombosis (UAT) is rare and few prenatally diagnosed cases have been reported. We describe 2 cases of fetal growth restriction prenatally diagnosed as UAT by ultrasound examination. In each case the cross section of the umbilical cord showed one normal artery and a small echogenic area which was suspected as an occluded thrombotic artery and they were surrounded by a highly curving 'C-shaped' vein. UAT was confirmed by histological examinations after deliveries in both cases. The characteristic ultrasound finding of the umbilical vessel, which is the so-called 'orange grabbed sign', enables the prenatal diagnosis of UAT and it is valuable with respect to perinatal fetal management because UAT is associated with increased perinatal morbidity and mortality.