Duration of Oxytocin and Rupture of the Membranes Before Diagnosing a Failed Induction of Labor

Abstract

Objective: To compare maternal and neonatal outcomes based on length of the latent phase during induction with rupture of membranes before 6 cm dilation.

Methods: This is a retrospective cohort study using data from the Consortium of Safe Labor study, including 9,763 nulliparous and 8,379 multiparous women with singleton, term pregnancies undergoing induction at 2 cm dilation or less with rupture of membranes before 6 cm dilation after which the latent phase ended. Outcomes were evaluated according to duration of oxytocin and rupture of membranes.

Results: At time points from 6 to 18 hours of oxytocin and rupture of membranes, the rates of nulliparous women remaining in the latent phase declined (35.9-1.4%) and the rates of vaginal delivery for those remaining in the latent phase at these time periods decreased (54.1-29.9%) Nulliparous women remaining in the latent phase for 12 hours compared with women who had exited the latent phase had significantly increased rates of chorioamnionitis (12.1% compared with 4.1%) and endometritis (3.6% compared with 1.3%) and increased rates of neonatal intensive care unit admission (8.7% compared with 6.3%). Similar patterns were present for multiparous women at 15 hours.

Conclusion: Based on when neonatal morbidity increased, in an otherwise uncomplicated induction of labor with rupture of membranes, a latent phase after initiation of oxytocin of at least 12 hours for nulliparous women and 15 hours in multiparous women is a reasonable criterion for diagnosing a failed induction.

Figure 1

Labor status by time from oxytocin and rupture of membrane. A. Nulliparous women (n=9,763); B. Multiparous women (n=8,379). Latent phase was defined as ending when cervical exam 6 cm achieved. Active phase was defined as starting when 6 cm dilation achieved. For example, by 6 hours duration of oxytocin and ROM in nulliparous women, 25.4% had delivered vaginally, 5.1% has a cesarean delivery in the active phase, 10.1% had a cesarean delivery in the latent phase, 23.6% were in the active phase and 35.9% were in the latent phase. These numbers are cumulative. All cases reaching vaginal or cesarean delivery outcomes from each former time point accumulated to the next time point.

Figure 2

Eventual vaginal delivery rates of women remaining in latent phase. A. Nulliparous women (n=9,763); B. Multiparous women (n=8,379). X-axis displays the duration of oxytocin and rupture of membranes. P-values for both nulliparous and multiparous women were both P <.001 (Cochran-Armitage Trend Test). % (number of women in the latent phase divided by all women).

Figure 3

Maternal outcomes of women remaining in latent phase compared with women in active phase or who had delivered. A. Nulliparous women (n=9,763); B. Multiparous women (n=8,379). X-axis displays the duration of oxytocin and rupture of membranes. Adjusted P-values were controlled for gestational age, race/ethnicity, body mass index (kg/m²) on admission, and hospital type. Latent phase was defined as ending when cervical exam 6 cm achieved. Active phase was defined as starting when 6 cm dilation achieved. *Adjusted P <.001; ^†adjusted P <.01; ^‡adjusted P <.05.

Figure 4

Neonatal outcomes of women remaining in latent phase compared with women in active phase or who had delivered. A. Nulliparous women (n=9,763); B. Multiparous women (n=8,379). Abbreviations: NICU, neonatal intensive care unit. X-axis displays the duration of oxytocin and rupture of membranes. Adjusted P-values were controlled for gestational age, race/ethnicity, body mass index (kg/m²) on admission, and hospital type. Latent phase was defined as ending when cervical exam 6 cm achieved. Active phase was defined as starting when 6 cm dilation achieved. *Adjusted P <.05; ^†adjusted P <.01.