Interpregnancy body mass index change and success of term vaginal birth after cesarean delivery

Abstract

We investigated the effect of interpregnancy body mass index (BMI) change on success of term vaginal birth after cesarean (VBAC) among normal, overweight and obese women. Using 1992-2009 Washington State birth certificate data linked with hospitalization records, we conducted a population-based retrospective cohort study of nulliparous women (BMI ≥18.5 kg/m(2)) with a primary cesarean in their first birth and a term trial of labor in their second. Interpregnancy weight change (difference between first and second prepregnancy BMIs) was categorized as maintenance (<1 BMI unit change), loss (≥1 unit), moderate gain (≥1 and <2 units), high gain (≥2 units). We estimated relative risks of VBAC success using generalized linear models with a log-link function, adjusting for maternal age, race/ethnicity, nativity, marital status, education, smoking, primary cesarean indication, interpregnancy interval, birth year for second birth, and prenatal care adequacy. Among 8302 women who attempted a term trial of labor, 65% had a successful VBAC. Women with normal BMI before their first pregnancy experienced an 8% decrease in VBAC success with moderate gain (relative risk [RR], 0.92; 95% confidence interval [CI], 0.87-0.98) and a 12% decrease in success with high gain (RR, 0.88; 95% CI, 0.83-0.93), compared with normal weight women who maintained weight. Weight loss increased VBAC success in women who were overweight (RR, 1.12; 95% CI, 1.01-1.25) or obese before their first delivery (RR, 1.24; 95% CI, 1.04-1.49), compared with overweight and obese women, respectively, who maintained weight. Women can improve their chance of successful VBAC through interpregnancy weight management.