Placental abnormalities associated with isolated single umbilical artery in small-for-gestational-age births

Previous studies have shown that pregnancies complicated by placentas with an isolated single umbilical artery (iSUA) are at increased risk for small-for-gestational-age (SGA) births. The etiology of SGA in this population, however, remains unknown.

The primary objective of this study was to evaluate whether placental abnormalities in pregnancies with SGA births differ according to the presence of iSUA.

This was an observational study of all women with pathologic examination of the placenta after delivering a non-anomalous, singleton SGA neonate between January 2009 and August 2015. SGA was defined as birthweight less than 10th percentile for gestational age. Women were categorized according to whether they had an iSUA or a three-vessel cord. The following placental pathologies were compared between the groups using bivariable and multivariable analyses: SGA placenta, maternal vascular malperfusion, high grade fetal vascular malperfusion, and chronic villitis.

1833 women were included in the analysis: 34 with iSUA and 1799 with three-vessel cord. More than 85% of women in both groups had at least one placental abnormality. After adjusting for nulliparity and neonatal gender, the presence of iSUA was associated with increased odds of high grade fetal vascular malperfusion (adjusted odds ratio 2.8, 95% confidence interval 1.1-7.5) and decreased odds of maternal vascular malperfusion (adjusted odds ratio 0.2, 95% confidence interval 0.1-0.9). There was no significant association with other pathologic findings.

Pathologic placental findings associated with SGA birth differed based on umbilical cord composition. The presence of iSUA in an SGA birth was associated with a higher odds of high grade fetal vascular malperfusion abnormalities and lower odds of maternal vascular malperfusion abnormalities, compared to SGA birth with a 3VC.