Absence of the ductus venosus with direct connection between the umbilicalvein and right atrium

Abnormalities of the ductus venosus are rare. We present the case of a dich orionic, diamniotic twin pregnancy in which complete absence of the ductus venosus, with direct communication between the umbilical vein and right atr ium, was detected in one infant on antenatal ultrasonography. Autopsy confi rmed the aberrant course. of the umbilical vein, which also had an abnormal histological structure. Associated congenital anomalies included an ostium secundum type atrial septal defect, absent inferior vena cava, single left pulmonary vein, stenosed right pulmonary artery, proliferation of the hepa tic arterioles with reduction of portal venules, and a duplex ureter. The l iterature is reviewed and pathogenesis relevant to this case is discussed.