Adverse maternal outcomes associated with major fetal malformations after singleton live birth

Major fetal malformations complicate approximately 2-5% of live births. It is unclear what impact fetal malformations have on severe maternal morbidity. To compare maternal outcomes between individuals with a fetus with major or minor fetal malformations compared to those without them. This was a secondary analysis of the Consortium on Safe Labor database. We limited the current analysis to pregnant individuals with a singleton live birth. We defined major fetal malformations based on the Centers for Disease Control and Prevention's (CDC) criteria. Fetal malformations which did not meet the criteria for major were categorized as minor. Our primary maternal outcome was severe maternal morbidity as defined by the CDC. Missing values were imputed by multiple imputation using the k-nearest neighbor imputation method. Poisson regression with robust error variance was utilized to obtain adjusted relative risks (aRR) with 95% confidence intervals (CI), controlling for confounders. Of 216,881 deliveries, there were 201,860 (93.1%) with no congenital malformation, 12,106 (5.6%) with minor fetal malformations, and 2845 (1.3%) with major fetal malformations. Compared to individuals with no fetal malformations, those with major fetal malformations were more likely to have severe maternal morbidity (0.7% vs. 1.2%; aRR 1.51 [95%CI 1.07-2.12]), postpartum hemorrhage (3.6% vs. 6.9%; aRR 1.76 [95%CI 1.50-2.06]), preeclampsia (5.1% vs. 8.3%; aRR 1.48 [1.31-1.67]), and cesarean delivery (26.7% vs. 42.3%; aRR 1.51 [1.45-1.58]). Compared to individuals with no fetal malformation, those with minor fetal malformations were more likely to have severe maternal morbidity (0.7% vs. 1.4%; aRR 1.73 [95%CI 1.48-2.02]), maternal death (0.01% vs. 0.03%; aRR 4.50 [1.18-17.19]), postpartum hemorrhage (3.6% vs. 6.1%; aRR 1.54 [95%CI 1.41-1.68]), preeclampsia (5.1% vs. 8.6%; aRR 1.50 [1.41-1.60]), superimposed preeclampsia (1.2% vs. 2.4%; aRR 1.25 [1.14-1.38]), cesarean delivery (26.7% vs. 39.6%; aRR 1.38 [1.35-1.41]), chorioamnionitis (3.0% vs. 4.7%; aRR 1.41 [1.29-1.53]), and postpartum endometritis (0.6% vs. 1.0%; aRR 1.58 [1.31-1.90]). Major and minor congenital fetal malformations are independent risk factors for severe maternal morbidity and other pregnancy complications.