Maternal Obesity Class as a Predictor of Induction Failure: A Practical Risk Assessment Tool

Objective To assess the impact of body mass index (BMI) on the rate of cesarean section (rCS) in induction of labor (IOL). Study Design A total of 7,543 singleton term pregnancies undergoing IOL (cervical dilatation at admission, CDA ≤ 3 cm) were divided according to BMI: underweight (n = 325); normal weight (NW) (n = 4,633); overweight (OW) (n = 1,610); and obese (n = 975). Age, parity, macrosomia, gestational age (GA), gestational weight gain (GWG), CDA, and IOL indications were considered. Results A higher rate of macrosomia (15.0 vs. 11.1%; p < 0.0001), earlier induction (GA 39.7 ± 1.3 vs. 40.1 ± 1.3 weeks; p < 0.0001) for maternal indications (39.1 vs. 21.1%; p < 0.001), and lower CDA (≤1cm; 66.4 vs. 61.4%; p < 0.005) were observed in obese versus NW. The rate of weight gain above the recommended range was higher in obese (obese 70.6% vs. NW 43.9%; p < 0.001), despite a significantly lower mean GWG compared with NW (14 ± 7.5 vs. 16.5 ± 5.6 kg; p < 0.001). Compared with NW, OW and obese demonstrated a significantly higher rCS (OW 31.1% and obese 36.9% vs. NW 24.7%; p < 0.001). BMI represented an independent factor affecting the rCS (vs. NW; OW odds ratio [OR] 1.4; confidence interval [CI] 1.2-1.7; p < 0.001; obese OR 2.3; CI 1.9-2.7 p < 0.001). Conclusion In the case of IOL, obesity represents an independent factor associated with a significant increase of CS to be considered during induction counselling.