Underweight at age 20 and pre-pregnancy and large-for-gestational-age births in Japanese women with gestational diabetes mellitus: Hamamatsu GRACE Study 4.

AIMS/INTRODUCTION: While maternal obesity is a well-established risk factor for large-for-gestational-age (LGA) infants, the impact of maternal underweight on LGA in women with gestational diabetes mellitus (GDM) remains inconsistent. This issue is particularly relevant in Japan, given the high prevalence of underweight women. We investigated the association between maternal weight and body mass index (BMI) at age 20 and pre-pregnancy and the risk of LGA in Japanese women with GDM. MATERIALS AND METHODS: This retrospective study analyzed 537 Japanese women with GDM. Participants were categorized by BMI (underweight <18.5 kg/m2, normal, and obesity ≥25.0 kg/m2) and by weight quartiles at age 20 and pre-pregnancy. Multivariable logistic regression analyses were performed to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for the association between underweight at age 20 and pre-pregnancy and LGA. RESULTS: The prevalence of underweight at age 20, underweight pre-pregnancy, and LGA was 30.4%, 13.4%, and 9.7%, respectively. After adjustment for confounders, underweight based on BMI at age 20 (adjusted OR 0.22, 95% CI: 0.06-0.75) and pre-pregnancy (adjusted OR 0.17, 95% CI: 0.03-0.64) was significantly and inversely associated with LGA compared with obesity. Similarly, the lowest weight quartiles at both time points were independently associated with a low risk of LGA. CONCLUSIONS: Maternal underweight at age 20 and pre-pregnancy was significantly associated with a lower risk of LGA in Japanese women with GDM. These findings suggest that weight status from early adulthood may play a crucial role in fetal growth outcomes.