Changes in prepregnancy body mass index between pregnancies and risk of primary cesarean delivery.

Objective: The objective of the study was to examine whether the risk and indications for primary cesarean in the second pregnancy are influenced by changes in prepregnancy body mass index (BMI) between pregnancies. Study Design: We performed a cohort analysis using the Missouri maternally linked birth and infant death surveillance datasets (1989-1997), comprised of women with their first 2 consecutive live births (n = 113,789). BMI (kilograms per square meter) was categorized as underweight (less than 18.5 kg/m²), normal (18.5 to 24.9 kg/m²), overweight (25 to 29.9 kg/m²), and obese (30 kg/m² or greater). Indications for primary cesarean were categorized as breech, dystocia, fetal distress, and others. Timing of primary cesarean was categorized as elective (prior to labor) and emergent (after initiation of labor). Adjusted odds ratio (OR) was used to quantify the associations between changes in prepregnancy BMI and indications for primary cesarean. Results: The rate of primary cesarean in the second pregnancy was 9.2%. Compared with women with normal BMI in their first 2 pregnancies, women who increased their BMI between pregnancies had increased risk of primary cesarean for all indications. Women who remained obese or overweight in both pregnancies were at increased risk of primary cesarean following breech (OR 1.28 and 1.13, respectively); dystocia (OR 1.94 and 1.41, respectively); fetal distress (OR 1.43 and 1.26, respectively); others (OR 3.17 and 1.63, respectively); and elective (OR 2.31 and 1.43, respectively) and emergent (OR 1.66 and 1.30, respectively) cesarean section. Women who lowered their BMI from obese to overweight or overweight to normal between pregnancies had risks of primary cesarean comparable with those with normal BMI in both pregnancies. Any increase in BMI from underweight to overweight or obese between the first 2 pregnancies was associated with increased risk of primary cesarean (OR 1.20 to 3.04) in the second pregnancy. Conclusion: Increases in prepregnancy BMI between first 2 pregnancies from normal to obese is associated with increased risk of indications for primary cesarean. The association between being overweight or obese or increases in prepregnancy BMI between pregnancies and primary cesarean in the second pregnancy suggests that counseling women with regard to their high BMI may be beneficial. [Copyright &y& Elsevier]