Associations of pre-pregnancy BMI and gestational weight gain with large-for-gestational-age in women with gestational diabetes mellitus in Southwestern China

Abstract Background Large-for-gestational-age (LGA) infants are a common complication of gestational diabetes mellitus (GDM), increasing the risk of obstetric trauma and long-term metabolic disorders. Pre-pregnancy body mass index (ppBMI) and gestational weight gain (GWG) are modifiable maternal factors, but their joint impact on LGA in sub-high-altitude, multiethnic populations remain unclear. Objective To examine the independent and combined associations of ppBMI and GWG with LGA risk among women with GDM in a sub-high-altitude, multiethnic region of southwestern China. Methods In this retrospective cohort study, clinical data from 407 women with GDM, diagnosed according to the Chinese national guideline (WS 331–2011) at 24–28 weeks of gestation, were analyzed. ppBMI and GWG were categorized according to national criteria. LGA was defined using Chinese birth weight references, with sensitivity analyses applying INTERGROWTH-21st standards. Multivariable logistic regression models evaluated independent and combined associations, adjusting for maternal age, infant sex, and gestational age at delivery. Sensitivity analyses additionally accounted for maternal insulin use, parity, and gravidity. Results Women with overweight/obese ppBMI combined with excessive GWG had the highest risk of LGA (adjusted OR 4.03, 95% CI 1.61–10.11). Excessive GWG among normal/underweight women showed a non-significant trend toward increased LGA risk (adjusted OR 2.60, 95% CI 0.95–7.14). Male infant sex was consistently associated with higher LGA odds. Findings were robust across sensitivity analyses and alternative birth weight standards. Conclusions Elevated ppBMI combined with excessive GWG is associated with higher LGA risk in women with GDM in sub-high-altitude, multiethnic regions. These findings are exploratory and hypothesis-generating, and may inform hypotheses for future research on BMI-stratified gestational weight patterns and potential intervention strategies. Prospective studies are warranted to confirm these associations and optimize maternal and neonatal outcomes.