BACKGROUND AND OBJECTIVE: The implications of the presence of a single umbilical artery (SUA) are unknown. Although most articles are based on selected samples, they suggest a relationship between SUA and malformations. Consequently, prenatal detection of SUA causes concern, since there are no definitive guidelines that can be followed after identification of this abnormality. The objective of this study was to comparatively analyze SUA in two series of consecutive births, with and without congenital defects. PATIENTS AND METHODS: A total of 19,909 cases and 19,148 controls from the Registry of the Spanish Collaborative Study on Congenital Malformations were studied. The variables analyzed were sex, birth weight, length, occipito-frontal circumference, gestational age, prematurity, delivery by caesarean section, umbilical cord length, placental weight, survival at 72 hours, primiparity, oligohydramnios, and polyhydramnios. Calculations included relative frequency, odds ratios (OR) and 95 % confidence intervals, the chi-square test, Fisher's p-value, and Student's t-test. RESULTS: SUA was found in 2.29 % of cases and in 1.03 % of controls (p = 0.0000001). These figures showed secular variation due to improvements in prenatal diagnosis and interruption of some pregnancies. When cases with and without SUA were compared, those with SUA had lower values of somatometry at birth, umbilical cord length and gestational age and had a higher risk for oligohydramnios, polyhydramnios, caesarean section, and death in the first 72 hours. Among controls, the only differences were a shorter umbilical cord and a higher frequency of oligohydramnios among infants with SUA. CONCLUSIONS: The results suggest that certain malformations associated with SUA could cause some of the differences among cases. Shortening of the umbilical cord and oligohydramnios could be related to SUA, as these abnormalities were found in both cases and controls. Comparison of cases and controls suggests that the etiopathogenesis of SUA could differ in the two groups.
