Pre-pregnancy body mass index and neonatal body weight in Japanese women with gestational diabetes mellitus: Hamamatsu GRACE Study 1.

Gestational diabetes mellitus (GDM) is closely associated with adverse fetal outcomes. Maternal underweight is associated with low birth weight (LBW) and small for gestational age (SGA). Despite the high proportion of underweight women with GDM in Asian populations, evidence on the association between underweight and the risk of LBW or SGA in GDM is limited and inconsistent. The aim of this study is to investigate this issue in Japanese women with GDM. We enrolled 641 women with GDM at the Hamamatsu University Hospital. Data on maternal body mass index (BMI), and fetal birth weight (including LBW and SGA) were collected from medical records. Logistic regression analysis was used to estimate crude odds ratios (ORs) and 95% confidence intervals (CIs) for the association between underweight and fetal birth weight. At pre-pregnancy, the prevalences of underweight (BMI <18.5 kg/m2), obesity (BMI ≥25 kg/m2), SGA, and LBW were 13.5%, 26.4%, 7.2%, and 13.3%, respectively. Pre-pregnancy underweight was independently and positively associated with SGA (adjusted OR: 2.56, 95% CI: 1.15-5.46) and LBW (adjusted OR: 3.07, 95% CI: 1.31-7.13). Obesity at age 20 but not at pre-pregnancy was independently and inversely associated with SGA (adjusted OR: 0.11, 95% CI: 0.01-0.88). In conclusion, among Japanese women with GDM, pre-pregnancy underweight, but not underweight at age 20, was significantly associated with SGA and LBW. On the other hand, obesity at age 20 was independently and inversely associated with SGA.