(1138) Association of body mass index and successful vaginal delivery with cervical dilation after ripening

Obese patients require induction of labor more frequently but also face increased rates of failed induction of vaginal delivery. This study sought to examine the relationship between cervical dilation after cervical ripening and vaginal delivery rates based on maternal body mass index (BMI) groups.

Study Design: This project was an IRB approved retrospective cohort study conducted at a single academic center. Nulliparous, term deliveries between January 1, 2020 and January 1, 2022 in patients age ≥18 with pre-pregnancy BMI ≥18.5. We excluded patients with multifetal gestation, pre-gestational diabetes, lethal fetal anomalies, prior cesarean delivery, and prisoner status, and those without documented cervical exam after cervical ripening.

Results: A total of 964 met inclusion/exclusion criteria.  There was an even distribution of patients between BMI categories consisting of 33.8% with a normal BMI, 31.1% overweight BMI and 35.1% patients who were classified as obese. In the entire cohort, increased cervical dilation at the end of cervical ripening was associated with higher rates of vaginal delivery with a mean of 3.7 centimeters for patients who underwent vaginal delivery and 3.2 centimeters for those who delivered via cesarean (p < 0.001). A logistic regression was performed to examine the interaction between maternal BMI group, cervical dilation after ripening and vaginal delivery rates which was not significant (p=0.11 for overweight and p=0.20 for obese patients) (Figure 1). However, after adjusting for BMI, the odds of having a vaginal delivery increased by 22% for every 1 unit increase in end cervical dilation (CI 1.12-1.34, p< 0.001). Compared to normal weight patients, after adjusting for end dilation, overweight patients were 30% less likely and obese 39% less  likely to have a vaginal delivery (p=0.046, p=0.003, respectively) (Figure 2).

Conclusion: While advancing cervical dilation increases rates of vaginal delivery overall, compared to normal weight patients, overweight and obese gravidas were less likely to have a vaginal delivery when adjusting dilation of the cervix after ripening.