Pre-pregnancy weight in Swedish women and the risk of gestational diabetes and subsequent type 2 diabetes—a population-based cohort study

Background: Obesity in young women is increasing. To which extent elevated pre-pregnancy overweight and obesity with and without gestational diabetes increase long-term risk of type 2 diabetes later in life has not been quantified. Methods: In a Swedish population-based cohort study we used data from the Swedish Medical Birth Registry in 1,153,074 primiparous women included in the registry between Jan 1, 1987 and Dec 31, 2019, with body mass index (BMI) at the first antenatal care visit as a proxy for pre-pregnancy weight to examine risk for gestational diabetes. We then compared women with gestational diabetes (n = 16,870) to age matched comparators (n = 81,862) and calculated hazards for developing type 2 diabetes identified from the National Diabetes registry over a median follow-up of 9 years. Findings: had an almost 10-fold risk of gestational diabetes compared to those with low-normal weight. Among women with gestational diabetes, the hazard of type 2 diabetes began to increase already at low- or normal weight, increasing nearly exponentially with rising BMI, while the increase in risk with increasing BMI among women without gestational diabetes was much less marked. No other social/pregnancy related factors improved the prediction of type 2 diabetes. Interpretation: Gestational diabetes serves as a stress test for developing type 2 diabetes, markedly amplifying risk in even women with normal pre-pregnancy weight, and with very high absolute rates in women with pre-pregnancy obesity. Future work should ascertain to which extent women with gestational diabetes have a structured follow-up after their pregnancy, and their subsequent prognosis. Funding: The Swedish Research Council; the Swedish governmental funding of clinical research (ALF); the Swedish Heart and Lung Foundation; and Diabetes Wellness.