Risk factors for small-for-gestational-age neonates in women with gestational diabetes mellitus: a retrospective nested case-control study

While gestational diabetes mellitus (GDM) is usually linked to fetal overgrowth, some pregnancies with GDM lead to small-for-gestational-age (SGA) infants. The underlying metabolic and clinical factors causing fetal growth restriction in GDM are not well understood. This study aimed to examine risk factors for SGA in GDM, focusing on maternal health profiles, glycaemic patterns, lipid metabolism, and weight gain during pregnancy. This retrospective nested case–control study included 684 women with GDM, comprising 342 with SGA neonates matched 1:1 to 342 non-SGA controls using propensity scores based on maternal age, gestational age, parity, pre-pregnancy body mass index (BMI), and conception method. Maternal demographics, metabolic parameters, glycaemic measures across gestation, lipid profiles, pregnancy weight-gain patterns, and perinatal outcomes were extracted from medical records. Group comparisons used t-tests or χ² tests. Multivariable logistic regression with multiple imputation identified independent predictors of SGA, supplemented by a complete-case sensitivity model. Women who delivered SGA infants had significantly lower total gestational weight gain, lower late-pregnancy fasting plasma glucose, higher post-prandial glucose, and reduced early-pregnancy HDL levels. Placental volume and weight were also markedly lower in the SGA group, and neonatal outcomes including fetal distress and NICU admission were more frequent. We noted that inadequate gestational weight gain (aOR 1.79, 95% CI 1.09–2.94, p = 0.02), higher late-pregnancy 2-hour glucose (aOR 1.27, 95% CI 1.10–1.48, p = 0.01), lower fasting plasma glucose (aOR 0.56, 95% CI 0.41–0.77, p = 0.01), and lower early HDL (aOR 0.40, 95% CI 0.22–0.73, p = 0.01) were significant predictors of SGA in adjusted models. In this matched cohort of women with GDM, insufficient gestational weight gain, abnormal late-pregnancy glucose patterns, and lower HDL concentrations in early pregnancy were identified as significant factors for SGA. Given the retrospective nature of the data, the evidence should be interpreted with caution.