Associations of Pregnancy History with BMI and Weight Gain in 45–54-Year-Old Women

BACKGROUND: Midlife women have a higher risk of cardiometabolic disease than younger women, but the lifelong biological/lifestyle factors responsible for this increase are unclear. OBJECTIVES: We investigated whether pregnancy history is a risk factor for midlife overweight/obesity and evaluated potential hormonal mechanisms. METHODS: The Baltimore Midlife Women's Health Study, a prospective cohort, recruited 772 women aged 45–54 y. Women reported pregnancy characteristics via questionnaires, trained staff measured weight/height to calculate midlife BMI, and serum hormones were assessed by ELISA. Logistic regression models assessed associations of pregnancy history with risk of midlife overweight/obesity and BMI gain since age 18. We additionally explored whether associations differed by menopausal status, and whether midlife hormones mediated relationships of pregnancy history and midlife BMI. RESULTS: These premenopausal or perimenopausal women were 66% Caucasian/White and 30% African American/Black, with a median of 2 live births (range: 0–11) and median age at first birth of 27 y (range: 12–46 y). Women with 0 and ≥2 live births had lower odds of overweight/obesity than those with 1 birth (OR = 0.47; 95% CI: 0.23, 0.96; P = 0.04, and OR = 0.58; 95% CI: 0.35, 0.95; P = 0.03, respectively). Women with ≥2 live births also had lower odds of BMI gain than those with 1 birth (OR = 0.66; 95% CI: 0.41, 1.06; P = 0.08). Furthermore, women who were older at their first birth had lower odds of overweight/obesity (OR = 0.96; 95% CI: 0.92, 1.00; P = 0.03) and BMI gain (OR = 0.97; 95% CI: 0.93, 1.00; P = 0.06). Number of pregnancies and age at last pregnancy were not associated with midlife overweight/obesity or BMI gain. Associations did not differ by menopausal status and were not explained by midlife hormones. CONCLUSIONS: Earlier childbirth and having 1 child increased women's risk of midlife overweight/obesity and BMI gain since age 18. Additional studies should focus on women's childbearing years as a critical determinant of midlife metabolic health.