Factors affecting success of vaginal delivery in nulliparous patients receiving magnesium sulfate during labor induction.

OBJECTIVE

Magnesium sulfate administration for preeclampsia with severe features during labor induction has been associated with increased risk of cesarean delivery (CD). We aim to evaluate associations with successful vaginal delivery (VD) in nulliparous patients undergoing labor induction while receiving magnesium sulfate.

METHODS

This was a secondary analysis from the Consortium on Safe Labor, a multicenter cohort study of 228,438 deliveries in 19 U.S. hospitals. The analysis included nulliparous women ≥18 years old with singleton gestation undergoing induction of labor for preeclampsia with severe features and receiving magnesium sulfate. Primary outcome was characteristics associated with successful VD. Secondary outcomes were maternal and neonatal outcomes. Chi-square and independent samples t-tests were used to compare groups. Multivariate logistic regression was performed to adjust for baseline characteristics that differed between groups.

RESULTS

A total of 4122 women met inclusion criteria, of whom 2256 (54.7%) had a VD. Patients who had a VD were more likely to have lower maternal age (24.8 ± 5.7 years vs. 27.0 ± 6.6 years; p < 0.001) and BMI (25.9 ± 6.5 kg/m2 vs. 27.8 ± 7.4 kg/m2; p < 0.001), higher gestational age (36w1 ± 4d vs. 35w ± 0d; p < 0.001), and lower admission systolic blood pressure (142.4 mmHg ± 17.2 vs. 146.0 mmHg ± 18.4; p = 0.049). Labor factors associated with VD included higher Bishop's score on admission (5.0 ± 3.1 vs. 3.2 ± 2.5; p < 0.001) and undergoing artificial rupture of membranes (aOR, 1.30; 95% confidence interval (CI), 1.02-1.65; p = 0.036) or oxytocin administration (aOR, 1.27; 95% CI, 1.07-1.50; p = 0.006). Successful VD was associated with lower postpartum hemorrhage (aOR, 0.15; 95% CI, 0.11-0.21; p < 0.001), blood transfusion (aOR, 0.61; 95% CI, 0.43-0.87; p = 0.007), and composite maternal morbidity (aOR, 0.66; 95% CI, 0.49-0.90; p = 0.009). In neonatal outcomes, VD was associated with higher one-minute APGAR (7.3 ± 2.1 vs. 6.8 ± 2.2; p < 0.001), and lower rates of NICU admission (aOR, 0.46; 95% CI, 0.39-0.55; p < 0.001) and composite neonatal morbidity (aOR, 0.66; 95% CI, 0.55-0.80; p < 0.001).

CONCLUSIONS

Rates of CD are high in patients undergoing induction of labor for preeclampsia with severe features and receiving magnesium sulfate. Various characteristics are associated with an increased rate of successful VD. Appropriate care should be taken in labor management for this high-risk patient cohort.