1. The rate of Cesarean delivery was similar between women receiving isosorbide mononitrate and those receiving placebo.
2. Women receiving isosorbide mononitrate were more likely to experience side effects.
Evidence Rating Level: 1 (Excellent)
Study Rundown: In the United States, nearly a third of women deliver during or after their 40th week of pregnancy. As gestational age increases beyond the 42th week (post-dates), the risk of complications such as fetal macrosomia, fetal dysmaturity syndrome, intrauterine infection, placental insufficiency, cord compression and neonatal mortality increases. To minimize the risk of these complications, current ACOG guidelines recommend induction of labor during the 42nd week of gestation. Prostaglandins are commonly used for cervical ripening and while they are associated with lower rates of Cesarean delivery compared to oxytocin for ripening, they’re also associated with side effects related to uterine hyperstimulation. As such, efforts have been made to identify a superior cervical ripening agent. Prior studies show that patients receiving isosorbide mononitrate had higher Bishop scores and were more likely to be in labor 12 to 24 hours later compared to those receiving placebo. The present work was the first to achieve adequate power to observe differences in rates of Cesarean delivery. The authors found that isosorbide mononitrate was associated with increased risk of side effects, including nausea, headache and diarrhea and did not affect a reduction in risk for Cesarean delivery.
Limitations of the study include higher rate of discontinued treatment in the isosorbide mononitrate group, which may have biased the results, and lack of comparison to existing cervical ripening agents. Future studies comparing isosorbide to prostaglandins, the current gold standard, are needed to better characterize efficacy and risks.
In-Depth [randomized controlled trial]: This study assessed the use of vaginal isosorbide mononitrate as a cervical ripening agent for women in their 41st week of pregnancy. Patients were randomized to receive either 40mg of isosorbide mononitrate (n=678) or placebo (n=684) vaginally every 2 days beginning at 41 0/7 weeks gestation, up to 3 doses. Incidence of Cesarean delivery as well as markers for maternal and perinatal morbidity and mortality were assessed.
Women in the isosorbide mononitrate group were equally likely to deliver by Cesarean compared to the placebo group (RR 1.00, CI 0.84-1.19). Women in the isosorbide mononitrate group were more likely to report side effects (RR 2.82, CI 2.49-3.20), including headache, nausea, faintness and diarrhea. Rates of complications including postpartum hemorrhage, low Apgar scores and prolonged NICU stays were comparable between the two groups.
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