Isolated single umbilical artery in twin pregnancies and its adverse pregnancy outcomes - a case report and review of literature

Single umbilical artery is the most common congenital abnormality of the umbilical cord and is seen in 4-11% of twin pregnancies. It is usually associated with intrauterine growth retardation, preterm labour, small-for-dates and other structural anomalies. There is no significant difference in the incidence between monochorionic and dichorionic twins. The left artery is usually absent more commonly than the right. The female co-twin was predominantly more affected than their male counterparts. Single umbilical artery is found twice more common in white women than in Afro-Asians and Americans. The hemodynamic disturbances occur early in the embryonic development, influence greatly in the development of single umbilical artery. Genetic and environmental factors also play a major role in the development of this anomaly. The pregnancies with single umbilical artery were classified as high risk group, because the overall perinatal mortality rate was estimated to be as high as 20%. There is a significant increase in the occurrence of single umbilical artery in pregnancies due to artificial reproductive technologies, as well as in spontaneous miscarriages. Prenatal ultrasonography is the principal diagnostic technique employed to identify single umbilical artery during 3(rd) trimester of pregnancy. The present case, reports the presence of a single umbilical artery in a monozygotic, monochorionic twin pregnancy, which is acardiac-acephalic fetus, small for dates, female sex, associated with other major structural anomalies, and was still born. Authors analyse its incidence, clinical presentations and pregnancy outcome and also review the pertinent literature.