Associations between high prepregnancy body mass index, breast-milk expression, and breast-milk production and...

Breast-milk expression is widely practiced by American mothers, but little is known about who expresses milk, how expression affects breastfeeding, or whether overweight or obese women, who have less breastfeeding success than do normal-weight women, express milk differently.

We investigated 1) whether breast-milk expression behavior differed by body mass index (BMI; in kg/m(2)) category and 2) whether the different breastfeeding behaviors of overweight (BMI: ≥25 and <30) and obese (BMI: ≥30) women resulted in different breastfeeding outcomes.

The subjects (n = 2288) provided information on BMI and breast-milk production, feeding, and expression in mail-in questionnaires as part of the Infant Feeding Practices Study II. Longitudinal and cross-sectional data were analyzed by using regression procedures adjusted for confounding.

Women of different BMI categories overall did not differ in whether, when, or why they expressed breast milk. Before 2 mo postpartum, however, obese women were more likely (P = 0.04, unadjusted) to try milk expression and were less likely (P = 0.01, unadjusted) to express milk successfully. In addition, overweight or obesity was associated (P < 0.03, unadjusted) with a shorter duration of breast-milk production only in women who never expressed milk. In overweight or obese women, those who ever expressed milk had longer durations of breastfeeding (P < 0.003, unadjusted) than did those who never expressed milk.

Breast-milk expression behaviors may differ by maternal BMI category only in the early postpartum period. In addition, breast-milk expression may reduce differences between BMI categories in the duration of breastfeeding and support longer durations of breastfeeding.