Single umbilical artery: Does it matter which artery is missing?

OBJECTIVE: Our purpose was to determine whether the presence of congenital anomalies in fetuses with a single umbilical artery is related to the side of the missing artery. STUDY DESIGN: During an 18-month prospective study, the side of the missing artery was identified in all pregnancies with a single umbilical artery (n = 77). Targeted sonograms and perinatal follow-up were obtained. RESULTS: The left umbilical artery was absent in 56 of 77 (73%) fetuses, compared with 21 of 77 (27%) for the right artery, p< 0.0001. Congenital anomalies occurred in 20 of 77 (26%) fetuses, with 16 of 56 (29%) in those with absence of the left artery and 4 of 21 (19%) in those with absence of the right artery, p = 0.561. Complex congenital anomalies occurred in 9 of 20 (45%) fetuses. All complex anomalies had absence of the left artery, p = 0.103. Cytogenetic abnormalities were noted in 6 fetuses, all with absence of the left artery, p = 0.181. In fetuses with a single umbilical artery as an isolated finding, small-for-gestational-age fetuses occurred in 4 of 50 (8%) pregnancies. CONCLUSION: In fetuses with a single umbilical artery the left artery is more commonly absent than the right artery. In our series cytogenetic and complex fetal anomalies occurred exclusively in fetuses with absence of the left artery. In contrast to previous reports, the incidence of small-for-gestational-age fetuses does not appear to be increased in cases of an isolated single umbilical artery.