From infancy to pregnancy: birth weight, body mass index, and the risk of gestational diabetes.

Obesity is a risk factor for gestational diabetes, whereas the role of the mother's birth weight is more uncertain. We aimed to investigate the combined effect of mothers' birth-weight-for-gestational-age and early pregnancy Body Mass Index (BMI) in relation to risk of gestational diabetes. Between 1973 and 2006, we identified a cohort of 323,083 women included in the Swedish Medical Birth Register both as infants and as mothers. Main exposures were mothers' birth-weight-for-gestational-age (categorized into five groups according to deviation from national mean birth weight) and early pregnancy BMI (classified according to WHO). Rates of gestational diabetes increased with adult BMI, independently of birth-weight-for-gestational-age. However, compared to women with appropriate birth-weight-for-gestational-age [appropriate-for-gestational age (AGA); -1 to +1 SD] and BMI (<25.0), women with obesity class II-III (BMI ≥ 35.0) had an adjusted odds ratio (OR) of 28.7 (95 % confidence interval, CI 17.0-48.6) for gestational diabetes if they were born small-for-gestational-age [small for gestational age (SGA); <-2SD], OR = 20.3 (95 % CI 11.8-34.7) if born large-for-gestational-age [large-for-gestational-age (LGA); >2SD], and OR = 10.4 (95 % CI 8.4-13.0) if born AGA. Risk of gestational diabetes is not only increased among obese women, but also among women born SGA and LGA. Severely obese women born with a low or a high birth-weight-for-gestational-age seem more vulnerable to the development of gestational diabetes compared to normal weight women. Normal pre-pregnancy BMI diminishes the increased risk birth size may confer in terms of gestational diabetes. Therefore, the importance of keeping a healthy weight cannot be overemphasized.