863: Gestational age and obesity as determinants of successful induction of labor

ObjectiveTo evaluate the association between induction of labor (IOL) and cesarean delivery (CD) by week of gestation at term. We also sought to evaluate the influence of obesity on this association.Study DesignA cross-sectional analysis of the association between CD and IOL was performed using demographic and obstetric data from Kentucky birth certificates (2004 – 2008). Nulliparous, singleton, non-anomalous, vertex gestations at 37 weeks or later were included. Unlabored CD were excluded. Bivariate analysis and multivariate logisitic regression were performed. Analysis was stratified by week of gestation and World Health Organization classification for body mass index (BMI).ResultsThere were 87,206 eligible births during the study years; 19,259 (22.1%) were delivered via CD. After controlling for maternal age, race/ethnicity, pre-pregnancy BMI, diabetic and hypertensive disorders, IOL was associated with CD (adjusted OR 1.6, 95% CI 1.6 – 1.7). The strength of this association varied by gestational age; the strongest association was at 37 weeks (adjusted OR 1.9, 95% CI 1.8 – 2.2) and the weakest association was at 39 weeks (adjusted OR 1.4, 95% CI 1.3 – 1.5). Both BMI (adjusted OR 1.06, 95% CI 1.059 – 1.065 per unit increase in BMI) and obesity (adjusted OR 2.1, 95% CI 2.0 – 2.2) were independent risk factors for CD. For 25 of the 30 gestational age-BMI combinations, IOL remained a significant risk factor for CD (range: adjusted OR 1.4 [95% CI 1.2 – 1.5] to adjusted OR 2.2 [95%CI 1.5 – 3.2]).ConclusionsGestational age is an important determinant of the likelihood of success of IOL. Labor induction was most successful at 39 weeks, and least successful at 37 weeks. Unexpectedly, we did not find a clear pattern of influence of obesity on the association between IOL and CD. While obesity is an important risk factor for CD, it did not appear to affect the relationship between IOL and CD. The success of IOL was a function of gestational age regardless of BMI. ObjectiveTo evaluate the association between induction of labor (IOL) and cesarean delivery (CD) by week of gestation at term. We also sought to evaluate the influence of obesity on this association. To evaluate the association between induction of labor (IOL) and cesarean delivery (CD) by week of gestation at term. We also sought to evaluate the influence of obesity on this association. Study DesignA cross-sectional analysis of the association between CD and IOL was performed using demographic and obstetric data from Kentucky birth certificates (2004 – 2008). Nulliparous, singleton, non-anomalous, vertex gestations at 37 weeks or later were included. Unlabored CD were excluded. Bivariate analysis and multivariate logisitic regression were performed. Analysis was stratified by week of gestation and World Health Organization classification for body mass index (BMI). A cross-sectional analysis of the association between CD and IOL was performed using demographic and obstetric data from Kentucky birth certificates (2004 – 2008). Nulliparous, singleton, non-anomalous, vertex gestations at 37 weeks or later were included. Unlabored CD were excluded. Bivariate analysis and multivariate logisitic regression were performed. Analysis was stratified by week of gestation and World Health Organization classification for body mass index (BMI). ResultsThere were 87,206 eligible births during the study years; 19,259 (22.1%) were delivered via CD. After controlling for maternal age, race/ethnicity, pre-pregnancy BMI, diabetic and hypertensive disorders, IOL was associated with CD (adjusted OR 1.6, 95% CI 1.6 – 1.7). The strength of this association varied by gestational age; the strongest association was at 37 weeks (adjusted OR 1.9, 95% CI 1.8 – 2.2) and the weakest association was at 39 weeks (adjusted OR 1.4, 95% CI 1.3 – 1.5). Both BMI (adjusted OR 1.06, 95% CI 1.059 – 1.065 per unit increase in BMI) and obesity (adjusted OR 2.1, 95% CI 2.0 – 2.2) were independent risk factors for CD. For 25 of the 30 gestational age-BMI combinations, IOL remained a significant risk factor for CD (range: adjusted OR 1.4 [95% CI 1.2 – 1.5] to adjusted OR 2.2 [95%CI 1.5 – 3.2]). There were 87,206 eligible births during the study years; 19,259 (22.1%) were delivered via CD. After controlling for maternal age, race/ethnicity, pre-pregnancy BMI, diabetic and hypertensive disorders, IOL was associated with CD (adjusted OR 1.6, 95% CI 1.6 – 1.7). The strength of this association varied by gestational age; the strongest association was at 37 weeks (adjusted OR 1.9, 95% CI 1.8 – 2.2) and the weakest association was at 39 weeks (adjusted OR 1.4, 95% CI 1.3 – 1.5). Both BMI (adjusted OR 1.06, 95% CI 1.059 – 1.065 per unit increase in BMI) and obesity (adjusted OR 2.1, 95% CI 2.0 – 2.2) were independent risk factors for CD. For 25 of the 30 gestational age-BMI combinations, IOL remained a significant risk factor for CD (range: adjusted OR 1.4 [95% CI 1.2 – 1.5] to adjusted OR 2.2 [95%CI 1.5 – 3.2]). ConclusionsGestational age is an important determinant of the likelihood of success of IOL. Labor induction was most successful at 39 weeks, and least successful at 37 weeks. Unexpectedly, we did not find a clear pattern of influence of obesity on the association between IOL and CD. While obesity is an important risk factor for CD, it did not appear to affect the relationship between IOL and CD. The success of IOL was a function of gestational age regardless of BMI. Gestational age is an important determinant of the likelihood of success of IOL. Labor induction was most successful at 39 weeks, and least successful at 37 weeks. Unexpectedly, we did not find a clear pattern of influence of obesity on the association between IOL and CD. While obesity is an important risk factor for CD, it did not appear to affect the relationship between IOL and CD. The success of IOL was a function of gestational age regardless of BMI.