Induction of labor with high- or low-dosage oral misoprostol-A Danish descriptive retrospective cohort study 2015-16

In Denmark, the rate of induced labor from 37 gestational weeks has increased by 108% from 12.4% in 2000 to 25.1% in 2012, and today more than 1 in 4 deliveries are induced. Standard procedure at North Zealand Hospital changed in 2016 from a dosage of 50 µg oral misoprostol 2-3 times daily, to 25 µg up to 8 times daily. Also, since 2016 healthy women with uncomplicated pregnancies (primiparous and multiparous) have been offered induction as an outpatient procedure. This study aimed to compare the current low-dosage procedure (25 µg) with the former high-dosage procedure (50 µg) in terms of induction to delivery time, maternal and fetal outcomes, and risk of uterine hyperstimulation.

Data from June 2015 to October 2016 were included. Comparable baseline, demographic, and obstetric data for women induced according to high-dosage or low-dosage protocols were retrieved from local medical files. Descriptive statistics, Pearson's chi-squared tests, Kaplan-Meier survival estimates, and logistic regression analyses were performed.

The study included 816 induced deliveries. The high- and low-dosage groups differed in rates of plurality and place of induction. Induction to delivery times lasting longer than 72 hours were significantly decreased in the low-dosage group (adjusted odds ratio [aOR] 0.48, 95% confidence interval [95% CI] 0.27 to 0.86). Women in the low-dosage group also less often needed additional induction (P = 0.02), and the rate of uterine hyperstimulation was low irrespective of protocol (1% vs 3%, P = 0.16). There were no cases of uterine rupture in either group. The probability of vaginal delivery in the low-dosage group increased (adjusted hazard ratio 1.27, 95% CI 1.08 to 1.49), as did the risk of delivery with vacuum extraction (aOR 2.27, 95% CI 1.24 to 4.15), whereas delivery by cesarean section slightly decreased (aOR 0.89, 95% CI 0.59 to 1.33). The risk of meconium-stained liquor was nonsignificantly decreased (aOR 0.82, 95% CI 0.55 to 1.23).

The low-dosage induction protocol was associated with favorable obstetric outcomes in terms of increased probability of vaginal delivery, but with higher risk of vacuum extraction. Protracted inductions and additional nonmedical interventions were reduced. There were no cases of uterine rupture. Statistically nonsignificant, the risk of uterine hyperstimulation was increased whereas the risk of meconium-stained liquor and of cesarean section was slightly decreased.