Time to Delivery After PROM at Term Is Shorter with Oxytocin than Buccal Misoprostol

After prelabor rupture of membranes (PROM) at term, standard care is to induce labor, which is associated with lower rates of chorioamnionitis and postpartum fever compared with expectant management. The optimal agent is unclear, however. Studies of buccal misoprostol are particularly scarce, even though buccally and vaginally administered misoprostol have similar bioavailability.

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In a retrospective cohort study, Mark A. Clapp, MD, MPH, a specialist in the Maternal-Fetal Medicine Program, OB/GYN Resident Taylor S. Freret, MD, EdM, and colleagues of the Department of Obstetrics and Gynecology at Massachusetts General Hospital, found that oxytocin was associated with significantly shorter admission-to-delivery intervals and fewer vaginal exams after PROM at term in nulliparous women with unfavorable cervical dilation, compared with buccal misoprostol. They report their findings in the American Journal of Perinatology.

Study Subjects and Institutional Protocols

The researchers reviewed the records of pregnant women who presented to Mass General with PROM at term between July 1, 2016, and June 30, 2017. They selected 130 women to study who were nulliparous, had a singleton fetus, had unfavorable (≤2 cm) or unknown cervical dilation, and had labor induced with one or more pharmacologic agents.

Of these subjects, 50 had (38.5%) received misoprostol and 80 had (61.5%) received oxytocin as the initial induction agent. The differences are described below:

• Misoprostol – Dosing was 50 mcg administered buccally every four hours for up to six doses. By protocol, patients were not candidates for initial or repeat misoprostol administration if they had a prior uterine scar, reported painful regular contractions or had significant fetal heart rate deceleration on monitoring
• Oxytocin – Medication was titrated according to a standardized, nurse-driven institutional protocol in which intravenous oxytocin is begun at 1 mU/min and increased by 1-2 mU/min no sooner than every 20 minutes to achieve and maintain contractions of moderate to strong intensity by palpation, occurring every two to three minutes, but not to exceed five contractions in 10 minutes, up to a maximum of 20 mU/min

Primary Outcome

The primary outcome was the time from admission to delivery. This was 19.9 hours with misoprostol and 16.9 hours with oxytocin (P = .01). In a linear regression analysis adjusted for differences in baseline characteristics between the two groups, the use of misoprostol was associated with a 22% longer time from admission to delivery (P = .01).

Secondary Outcomes

Patients who received oxytocin had a lower median number of vaginal exams than those who received misoprostol (three vs. four, P = .009). There was no difference between induction agents in the number of patients who reached the second stage, mode of delivery or rates of chorioamnionitis, neonatal resuscitation or admission to the neonatal intensive care unit.

Reflections

The use of oral or buccal prostaglandins such as misoprostol came about because of concern over the risk of ascending infection and neonatal harm related to vaginal exams required to place the prostaglandins. Although in this study there was no difference between induction agents in rates of chorioamnionitis, the increased number of exams with misoprostol administration and the longer labor times should increase the concern about potential infectious risks.

The higher number of vaginal exams with misoprostol probably reflects the fact that providers tend to transition patients from misoprostol to oxytocin once the cervix is favorable, and additional exams are required to assess whether that has occurred.

The study findings also have cost implications. Prior literature has emphasized that oral or buccal misoprostol is a relatively inexpensive induction method compared with oxytocin. However, the cost for three additional hours of intrapartum care between admission and delivery may outweigh any savings related to the cost of the induction method itself.

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