A 20-year prospective study of childbearing and incidence of diabetes in young women, controlling for glycemia before conception - The Coronary Artery Risk Development in Young Adults (CARDIA) Study

OBJECTIVE-We sought to determine whether childbearing increases incidence of type 2 diabetes after accounting for preconception glycemia and gestational glucose intolerance. RESEARCH DESIGN AND METHODS-A prospective, biracial cohort was examined up to five times during 1985-2006 in the multicenter, U.S. population-based Coronary Artery Risk Development in Young Adults Study. The analysis included 2,408 women (1,226 black and 1,182 white) aged 18-30 years who were free of diabetes and had a fasting plasma glucose (FPG) < 126 mg/dl at baseline. Incident diabetes was diagnosed by self-report, diabetes medication use, FPG >= 126 mg/dl, and/or plasma glucose >= 200 mg/dl after a 2-h oral glucose load. Time-dependent interim birth groups were those with zero and those with one or more births with or without gestational diabetes mellitus (GDM), stratified by baseline parity. Complementary log-log models estimated relative hazards of incident diabetes by interim births adjusted for age, race, family history of diabetes, and baseline covariates (FPG, BMI, education, smoking, and physical activity). RESULTS-Of 193 incident diabetes cases in 42,782 person-years (4.5 cases/1,000 person-years), 84 (44%) had one or more interim births. Among nulliparas at baseline, incident rates per 1,000 person-years were 3.2 (95% CI 2.4-4.1) for those with no births, 2.9 (1.8-3.9) for one or more births without GDM, and 18.4 (10.9-25.9) for one or more births with GDM; adjusted relative hazards (95% CI) were 0.9 (0.6-1.4) for one or more births without GDM and 3.8 (2.2-6.6) for one or more births with GDM versus no births. CONCLUSIONS-Childbearing did not elevate diabetes incidence among those with normal glucose tolerance during pregnancy (without GDM). GDM conferred the highest risk of developing diabetes independent of family history of diabetes and preconception glycemia and obesity.