Factors Affecting BMI Changes Among Lactating and Non-Lactating Mothers in the First Year Postpartum

Background: Pregnancy and the postpartum periods are times of increased vulnerability for excess weight gain and retention and, in turn, increased risks for long-term obesity for women. Methods: Secondary analyses were conducted on measured anthropometric data from two groups of women distinct in infant feeding modality (never breastfed [n=112] vs. breastfed exclusively [n=96]) collected monthly from 0.5 months (baseline) to 1 y post-partum. Prepregnancy BMI was self-reported and psychological eating behavior traits were evaluated by questionnaire at baseline. Linear mixed-effects models examined the trajectories of percent change in BMI from baseline over time (primary outcome). Differences in BMI from prepregnancy to 1 y (secondary outcome) were examined. Results: While both prepregnancy weight status and infant feeding modality had independent effects, the benefits of lactation on BMI trajectories differed based on prepregnancy BMI. When compared to lactating women, non-lactating women had significantly slower initial rates of BMI loss if prepregnancy healthy weight (ß = 0.63, 95% CI: 0.19, 1.06), overweight (ß = 2.10, 95% CI: 1.16, 3.03), and a tendency if with obesity (ß = 0.60, 95% CI: -0.03, 1.23). Among those with overweight, a greater percentage of non-lactating women gained > 3 BMI units by 1 y (47% vs. 9%; p