Congenital Malformations Associated With a Single Umbilical Artery in Twin Pregnancies.

A single umbilical artery (SUA) was identified in 1.5% of twin pregnancies. The presence of a SUA in a twin pregnancy was associated with a 50% incidence of fetal anomalies, many of them complex and severe. The embryology and pathophysiological mechanisms associated with a SUA are reviewed. Aneuploidy is relatively common and should be considered, particularly in the presence of associated anomalies. Fetal growth restriction is frequent and preterm delivery is common.