Single umbilical artery. A statistical analysis of 237 autopsy cases and review of the literature.

Two hundred thirty-seven autopsy cases of SUA and 1,242 unselected perinatal autopsies from military hospitals were reviewed and statistically analyzed. Results were correlated with those found in a comprehensive literature review. Incidence: The incidence of SUA in prospective deliveries is about 1%. Incidence is related to the portion of the umbilical cord examined, the method of cord examination (gross or microscopic), and to the race of the population base. The incidence of SUA in autopsy series is about twice the incidence in prospective series. SUA has a much higher incidence amont malformed, stillborn, or spontaneous abortuses than among apparently normal, liveborn, or induced abortuses. The incidence of SUA is less among very early embryos than among newborns because of the likelihood that SUA results from secondary atrophy of a preexisting normally formed second artery. As gestation proceeds, more cases will have become manifest to increase the incidence of SUA. There is no evidence of a familial tendency for SUA. SUA occurs slightly more frequently in females than in males, although there is a greater tendency for males with SUA to be malformed. The prognosis for SUA males is worse than for SUA females but no worse than that for male infants, in general. There is no relationship between the incidence of SUA and the month of the mother's last menstrual period. SUA and multiple births: The incidence of twins among SUA infants is at least three times greater than the overall incidence of twins. SUA occurs three to four times more frequently among twins than among Singletons. Although twin infants are subject to twice the expected incidence of malformations, twin SUA infants have no greater incidence of associated malformations than SUA singletons. Most SUA twins are discordant for the anomaly with SUA occurring in the smaller twin. The increased incidence of SUA among twin infants is not due to a greater incidence among monozygotic twins, since there is little difference from the usual proportion of monozygotic and dizygotic twins among twins with SUA. Mortality: In prospective series the mean perinatal mortality is about 20.0%. Approximately two-thirds of the perinatal deaths are stillborn and one-third are liveborn; and of the stillborn SUA infants, approximately three-quarters die antepartum and one-quarter die intrapartum. Mortality of SUA infants is related to associated fetal and placental malformations, prematurity and low birth weight, and intrauterine growth retardation. Although associated malformations are the primary cause of the high perinatal mortality, even nonmalformed SUA infants have an increased mortality rate.(ABSTRACT TRUNCATED AT 400 WORDS)