Early Versus Late Amniotomy Following EAB Cervical Ripening - Does Parity Matter?

Induction of labor is a common obstetric procedure with a reported rate of 23.3% in 2012 in the United State. It has been recently reported that Induction of labor at full term in uncomplicated singleton gestations is not associated with increased risk of cesarean delivery and overall has similar outcomes compared to expectant management.

Induction of labor in women with an unripened cervix is comprised of two stages, cervical ripening followed by augmentation of labor.

Extra amniotic balloon inflation is a widespread mechanical method of cervical ripening that commonly results in a ripened cervix open to 3-4 cm without significant uterine contractions. At this point the clinician may opt to perform artificial rupture of membranes or rather first begin oxytocin infusion delaying amniotomy to later stages of labor. A retrospective cohort showed early amniotomy after Foley balloon catheter removal was associated with shorter duration of labor induction among nulliparous women.In accordance, an RCT investigating the efficacy of early amniotomy in nulliparous women showed this practice resulted in labor shortening without increasing the rate of cesarean section, yet these women were treated by different methods for cervical ripening. Contradicting results were shown in a randomized controlled trial addressing the very question of early versus late amoniotomy after balloon ripening, concluding that postponing amniotomy until active labor commences results in a reduction of dystocia indicated cesarean section. However no distinction was made in this study between nulliparous and multiparous parturients. Since these comprise different groups with distinct labor curves, the question remains whether one should consider parity when deciding to perform early vs late amniotomy following balloon expulsion.

Both Amniotomy and Oxytocine infusion are part of the routine protocol and necessary procedures for induction of labor. Adverse outcome of amniotomy includes fetal heart rate changes, cord prolapse and intrapartum fever when labor is prolonged. Adverse outcome of oxytocine include hypertonus and fetal heart rate changes requiring cessation of oxytocine infusion (as in routine protocol) and intrapartum fever if labor is prolonged (not due to oxytocine infusion per se). Most of the patients admitted for induction of labor will need both amniotomy and oxytocine, however the role of the order of these two procedures is unclear ,as well as whether the order of these procedures affect the rate of adverse outcome.

The objective of this study is to investigate the course of labor in early versus late amniotomy following balloon cervical ripening in women undergoing term induction of labor stratified by parity.