Induction of labor remains a significant risk factor for cesarean delivery (CD). Amniotomy is generally thought to be inexpensive and safe, but studies have not investigated the efficacy of the procedure in nulliparous women. This unblinded, randomized controlled trial was undertaken to determine whether early amniotomy, defined as artificial rupture of the membranes (AROM) at 4-cm dilation or less, would reduce the duration of labor or increase the proportion of women delivered within 24 hours. The safety of early amniotomy was assessed for adverse obstetric outcomes and maternal and neonatal infectious morbidities.
Inclusion criteria were nulliparity, singleton, term gestation, and a need for labor induction as determined by the treating physician. Patients were randomly assigned to early amniotomy or to standard management, which was amniotomy at greater than 4-cm dilation. In the early amniotomy group, amniotomy was performed as early as could be done safely. No specific instructions were given regarding the timing of amniotomy in the standard treatment group. This decision and decisions for the primary method of induction and other intrapartum/postpartum factors were made at the physician’s discretion. The primary outcomes were time from initiation of induction, defined as time at delivery of the first induction method to delivery, and the proportion of women delivered within 24 hours from the initiation of induction. Secondary end points included rates of and indications for CD, chorioamnionitis, postpartum fever, wound infection, endomyometritis, neonatal intensive care unit (NICU) admission, and suspected neonatal sepsis. Statistical analyses were performed with the intent-to-treat principle. Continuous outcomes were compared with the use of the Student t test or Mann-Whitney U dependent on their distributions; dichotomous outcomes were assessed with χ2 or Fisher exact tests. Time to delivery was not normally distributed and was compared with the use of the Mann-Whitney U test.
Of 749 women screened for eligibility, 84 women (11.2%) were ineligible by exclusion criteria. Of the 635 eligible nulliparous women, 585 women (92%) consented and were assigned randomly, with 292 women in the early amniotomy group, and 293 women in the standard treatment group. The groups were similar in demographics and maternal medical conditions; the mean gestational age at induction was 22.7 ± 5.8 years and 23.3 ± 6.2 years in the early amniotomy and standard groups, respectively. The admission cervical dilations were 1.1 ± 1.03 and 1.1 ± 0.97 cm, respectively. The indications for labor induction were similar between the groups, with the most common indications being more than 40-week gestations and gestational hypertension/preeclampsia. Most women received misoprostol, and about 30% of the women received a Foley bulb; 73% of women in both groups received more than 1 agent for induction. The average time from the start of induction to delivery was 19.0 hours in the early amniotomy group compared with 21.3 hours in the standard group (P = 0.04). This difference in length of labor occurred mainly in the first stage, which was defined as time from randomization assignment to complete cervical dilation. In the early amniotomy group, 68% of women were delivered within 24 hours of the start of induction compared with 56% in the standard treatment group (P = 0.002). However, rates of CD did not differ between the groups. The rate of chorioamnionitis was 11.5% in the early amniotomy group and 8.5% in the standard group, not a statistically significant difference. Two cord prolapses occurred in the early amniotomy group (both infants did well), but none in the standard group. The groups did not differ in the rate of confirmed or suspected neonatal sepsis or admission to the NICU.
These results indicate that early amniotomy shortens labor by about 2 hours and increases the proportion of women delivered within 24 hours, but does not increase the rate of CDs. The shorter duration of labor must be weighed against both maternal and neonatal safety concerns. Although chorioamnionitis did not lead to an increase in the rate of suspected neonatal sepsis or NICU admission, and no serious maternal consequences developed, future studies should focus on the occurrence of chorioamnionitis with early amniotomy. Based on data from this study, early amniotomy may be a useful adjunct in nulliparous labor inductions and may be incorporated into induction algorithms.
Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine, St Louis, MO