52 Vaginal isosorbide mononitrate for labor induction in pregnancies complicated by hypertensive diseases of pregnancy

Abstract

Pregnancies with hypertensive diseases of pregnancy (HDP) often require induction of labor to minimize maternal and fetal risks. There is no superior method of labor induction and rates of cesarean delivery (CD) range from 15-60% in this population. Nitric oxide donors decrease maternal blood pressure and soften the cervix without inducing uterine contractions. We hypothesized that addition of vaginal isosorbide mononitrate (IMN) to vaginal misoprostol for labor induction may decrease the rate of CD and need for intrapartum emergent antihypertensive therapy in pregnancies complicated by HDP. This was a double-blind, placebo-controlled, randomized trial of women with singleton pregnancy ≥24 weeks gestation with an induction of labor for HDP between 11/2017-2/2020. Participants were eligible if Bishop score less than 6 and cervical dilation ≤2cm. They received up to 3 doses of 40mg IMN and 25mcg vaginal misoprostol in addition to standard interventions for induction - foley and oxytocin. Primary outcome was rate of cesarean delivery. Secondary outcomes included indication for CD, length of labor, use of intrapartum emergent antihypertensives, and maternal and neonatal morbidities. A sample size of 176 women was needed to detect at least a 20% difference in the primary outcome (Power 0.8). 89 women were randomized to the IMN group and 87 to the placebo group. GA at delivery were similar between groups (37 [34-38] vs 37 [35-38]). CD rates were similar with between both (32.6% vs 25.3%; RR, 1.29; 95% CI, 0.81 to 2.06; P=0.39). Neither length of labor nor use of intrapartum emergent antihypertensives was significantly different. Maternal headache was more common in IMN group than placebo group (47.2% vs 27.0%; RR, 1.52; 95% CI, 1.04 to 2.23; P=0.04), whereas clinical chorioamnionitis was less common in the IMN group (0% vs 8%; P=0.02). Adding vaginal IMN to vaginal misoprostol for labor induction in pregnancies complicated by HDP did not result in fewer CD.