The missing umbilical artery. I. Prospective study based on a maternity unit.

In a consecutive series of nearly 20,000 freshly delivered placentas, 2 vessels instead of the normal 3 were found in the umbilical cords of 143 (0·72%) infants, 83 females and 60 males. 4 infants were twins: in each instance the co-twin had 3 vessels. The incidence of single umbilical artery (SUA) in multiple pregnancies was slightly less than in singletons. 2 infants with SUA were sibs. There was an increased incidence of major malformations (17·5%), of prematurity (16·5%), and of smallness for dates (34%) among infants with SUA. 25 (17·5%) infants, of whom 19 had a major malformation, died in the perinatal period; of these, 2 had a persistent vitelline artery. (A follow-up study has been carried out on the surviving infants—results to be published.) This investigation into the incidence and significance of SUA is based on what is so far the largest prospective and unselected series collected in a single maternity unit. All placental examinations and necropsies were carried out by one pathologist, all follow-up examinations by one paediatrician.