We investigated whether changes in interpregnancy body mass index (BMI) influence the risk of gestational and type 2 diabetes among a cohort of women with two consecutive live, singleton births of 20–44 weeks gestation (n = 232,272).

Logistic regression models were used to examine the risk for development of gestational or type 2 diabetes during the second pregnancy. Mothers with normal weight for both pregnancies (normal-normal) served as the referent group.

Across all BMI categories, mothers with significant weight gain (i.e., moving from a lower BMI category into a higher category) had an increased risk for the development of diabetes. Mothers who moved from normal prepregnancy weight (BMI = 18.5–24.9 kg/m²) in the first pregnancy to obese prepregnancy weight (BMI ≥ 30.0 kg/m²) in the second pregnancy showed the greatest increment in risk. These mothers exhibited a threefold risk for developing diabetes (OR = 3.21, 95% CI 2.76–3.73). Mothers who maintained their interpregnancy BMI weight category or who moved to a lower BMI category had reduced risk for gestational and type 2 diabetes. The risk associated with mothers who moved to a lower BMI category was approximately half that of the normal-normal BMI category.

Interpregnancy weight gain is associated with a dose–response increase in risk of diabetes. Establishing a normal interpregnancy BMI may reduce the risk of diabetes.