Predictive value of glycated hemoglobin levels for large for gestational age infants in women with pregestational diabetes according to body mass index.

Objective: To evaluate whether pre-pregnancy body mass index (BMI) modifies the predictive ability of glycosylated hemoglobin (HbA1c) for large for gestational age (LGA) infants in women with pregestational diabetes. Methods: This multicenter retrospective cohort study included 402 women with pregestational diabetes from 17 University Hospitals in South Korea. Pregestational diabetes included early-diagnosed gestational diabetes, type 1 diabetes, and type 2 diabetes. Participants were categorized by pre-pregnancy BMI (<25 vs. ≥25 kg/m2). The primary outcome was LGA birth. Logistic regression was used to assess the association between trimester-specific HbA1c levels and LGA in each BMI group. Receiver operating characteristic (ROC) curve analysis evaluated predictive performance. Results: Among 402 women, 183 (45.5%) had a BMI <25 kg/m2 and 219 (54.5%) had a BMI ≥25 kg/m2. In the BMI <25 kg/m2 group, higher HbA1c levels in all trimesters were significantly associated with an increased risk of LGA, with the strongest association in the third trimester (odds ratio [OR], 2.28; 95% confidence interval [CI], 1.46-3.58). In women with BMI ≥25 kg/m2, only third-trimester HbA1c was significantly associated with LGA (OR, 1.455; 95% CI, 1.069-1.981). ROC analysis showed moderate discrimination for LGA prediction in women with BMI <25 kg/m2 (area under the curve [AUC], 0.70-0.82), but poor discrimination in those with BMI ≥25 kg/m2 (all AUCs ≤0.65). Conclusion: The predictive utility of HbA1c for LGA differed according to pre-pregnancy BMI and was greater in women with BMI <25 kg/m2 than in those with BMI ≥25 kg/m2.