Parity and body mass index in U.S. women: a prospective 25-year study

OBJECTIVE: To investigate long-term body mass index (BMI) changes with childbearing. DESIGN AND METHODS: Adjusted mean BMI changes were estimated by race-ethnicity, baseline BMI and parity using longitudinal regression models in 3943 young females over 10 and 25 year follow-up from the ongoing 1979 National Longitudinal Survey of Youth cohort. Results: Estimated BMI increases varied by group, ranging from a low of 2.1 BMI units for white, non-overweight nulliparas over the first 10 years to a high of 10.1 BMI units for black, overweight multiparas over the full 25-year follow-up. Impacts of parity were strongest among overweight multiparas and primaparas at ten years, ranges 1.4–1.7 and 0.8–1.3 BMI units, respectively. Among non-overweight women at 10 years, parity-related gain varied by number of births among black and whites but was unassociated in Hispanic women. After 25 years, childbearing significantly increased BMI only among overweight multiparous black women. CONCLUSION: Childbearing is associated with permanent weight gain in some women, but the relationship differs by maternal BMI in young adulthood, number of births, race-ethnicity and length of follow-up. Given that overweight black women may be at special risk for accumulation of permanent, long-term weight after childbearing, effective interventions for this group are particularly needed.