For this study, researchers wanted to evaluate the prevalence of unsuccessful induction of labor and the patient risk factors associated with it. Researchers conducted case-control research on a group of nulliparous women who gave birth between 39 and 41 weeks of gestation after being induced in one of seven hospitals. The Obstetric Care Consensus criteria were used to define causes of failed induction (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 unsuccessful induction, the following four women who did not satisfy the criteria for failed induction of labor were chosen for the control group, and they were matched by the hospital. A multivariate conditional logistic regression with a backward stepwise variable selection approach was used to identify features related to failure induction of labor.

Across the hospitals, 4,123 of 10,175 nulliparous women (40.5%) were induced, with 82 of them experiencing a failed induction of labor (2.0%). For the matching control group, a total of 328 women were chosen. The groups had comparable baseline characteristics. Women with a failed induction were more likely than women in the control group to have a delivery BMI of 40 or above (28.0 vs 8.2%, P<.001), shorter height (mean 63.9 vs 64.8 inches, P=.01), and a closed cervix on admission (41.5 vs 24.1%, P=.002). In the multivariable model, the following factors were significantly associated with induction failure: delivery BMI (aOR 7.93, 95% CI 3.48–18.09, for BMI 40 or higher relative to BMI less than 30), height in inches (aOR 0.89, 95% CI 0.80–0.98), and a number of centimeters dilated on admission 2 or more (aOR 0.30, 95% CI 0.14–0.65).

It was uncommon for labor induction to fail. Shorter stature, a BMI of 40 or greater, and cervical dilatation of less than 2 cm on admission were all risk factors. Despite this, the majority of women with these risk factors would not have a failed labor induction.