The impact of maternal obesity and weight gain on vaginal birth after cesarean section success

Objective

This study was undertaken to determine the impact of maternal obesity on success of a trial of labor (vaginal birth after cesarean section [VBAC]) after a single low transverse cesarean delivery.

Study design

Individual charts of women with low transverse cesarean delivery in their first viable pregnancy who underwent a VBAC in their second viable pregnancy at our urban tertiary care institution were reviewed. Maternal body mass index (BMI) was classified as underweight (<19.8 kg/m²), normal (19.8-24.9 kg/m²), overweight (25-29.9 kg/m²), or obese (≥30 kg/m²). Clinical characteristics and labor outcomes were assessed. Factors potentially affecting VBAC success were analyzed by univariate analysis. Logistic regressions were performed to determine the impact of maternal pregravid BMI on VBAC success after controlling for confounding factors.

Results

Of 510 women attempting a trial of labor, 337 (66%) were successful and 173 (34%) failed VBAC. Decreased VBAC success was seen in obese (54.6%) but not overweight (65.5%) women compared with women of normal BMI (70.5%), P=.003 and .36, respectively. Underweight women had more VBAC success than women of normal BMI (84.7% vs 70.5%, P=.04). Controlling for other factors, the association between increasing pregravid BMI and BMI ≥30 kg/m² with decreased VBAC success persisted, P=.03 and .006, respectively. Normal BMI women who became overweight before the second pregnancy had decreased VBAC success compared with those whose BMI remained normal (56.6% vs 74.2%, P=.006). However, overweight women who decreased their BMI to normal before the second pregnancy did not significantly improve VBAC success (64.0% vs 58.4%, P=.67).

Conclusion

Increasing pregravid BMI and weight gain between pregnancies reduce VBAC success after a single low transverse cesarean delivery.

Key words: Obesity, Body mass index, Vaginal birth after cesarean, Trial of labor