Incidence of and Risk Factors for Failed Induction of Labor Using a Contemporary Definition

Abstract

Objective: To estimate the incidence of failed induction of labor and the associated patient risk factors.

Methods: We performed a case-control study from a cohort of nulliparous women who delivered between 39 and 41 weeks of gestation after an induction of labor in one of seven hospitals. Cases of failed induction were defined using the Obstetric Care Consensus criteria (ie, cesarean delivery performed in early labor [less than 6 cm dilatation] after at least 12 hours of oxytocin administration from membrane rupture). For each case of failed induction, the next four women who did not meet the criteria for failed induction of labor were selected for the control group, matched by hospital. We identified characteristics associated with failed induction of labor using a multivariable conditional logistic regression that was constructed with backward stepwise method for variable selection.

Results: Across the hospitals, 4,123 of 10,175 nulliparous women were induced (40.5%), of whom 82 had a failed induction of labor (2.0%). A total of 328 women were selected for the matched control group. Baseline characteristics were similar between the groups. Compared with women in the control group, women with a failed induction were more likely to have a delivery body mass index (BMI) of 40 or higher (28.0 vs 8.2%, P<.001), shorter height (mean 63.9 vs 64.8 inches, P=.01), and closed cervix on admission (41.5 vs 24.1%, P=.002). Factors significantly associated with induction failure in the multivariable model included: 1) delivery BMI (adjusted odds ratio [aOR] 7.93, 95% CI 3.48-18.09, for BMI 40 or higher relative to BMI lower than 30, 2) height in inches (aOR 0.89, 95% CI 0.80-0.98), and 3) number of centimeters dilated on admission 2 or more (aOR 0.30, 95% CI 0.14-0.65).

Conclusion: Failed induction of labor occurs infrequently. Risk factors include shorter height, BMI 40 or higher, and cervical dilatation of less than 2 cm on admission. Even so, most women with these risk factors will not experience failed labor induction.