Differences in association between gestational weight gain and perinatal outcomes according to pre-pregnancy body mass index categories and gestational diabetes mellitus status: findings from a large Japanese cohort

Introduction We aimed to examine the impact of gestational weight gain (GWG) on perinatal outcomes based on body mass index (BMI) category and gestational diabetes mellitus (GDM) status. Research design and methods This retrospective study included 53 183 Japanese women with GDM and 734 028 with normal glucose tolerance (NGT). We assessed interaction effects of BMI categories (underweight <18.5, normal 18.5–24.9, overweight 25.0–29.9, obese ≥30.0 kg/m²) and GDM status on GWG and perinatal outcomes, including birth weight, hypertensive disorders of pregnancy, preterm delivery, mode of delivery, and a composite outcome, using generalized linear models with a logit link function. Results BMI category and GDM status had significant interaction effects on the association between GWG and all outcomes (all p<0.05, using the likelihood ratio test). Notably, the impact of increased GWG on the risk of having large-for-gestational-age newborns was greater in women with GDM than in those with NGT, a trend that was most pronounced in the obese group. For GWG, from 5–6 kg to 15–16 kg, the predicted probability of large-for-gestational-age newborns increased by 10.0% (from 4.9% to 14.9%) for NGT compared with 15.6% (from 6.3% to 21.8%) for GDM in the normal BMI group, and by 14.4% (from 17.6% to 32.0%) and 23.1% (from 23.5% to 46.6%), respectively, in the obese group. Conclusions The impact of GWG on perinatal outcomes differed according to the BMI category and GDM status. These findings support the need to take into account both factors when developing GWG recommendations to minimize the risk of adverse perinatal outcomes.