The influence of maternal complications on small for gestational age in very preterm, late preterm and term pregnancies: a Chinese study

Abstract

This study aimed to assess the association between single or combined maternal complications and small-for-gestational-age (SGA) birth among very preterm, late preterm, and term births and to evaluate whether this association varied across gestational periods. This retrospective cross-sectional study included 46,829 singleton pregnancies. The maternal complications considered were gestational hypertension (GH), preeclampsia (PE), and gestational diabetes mellitus (GDM). The potential nonlinear association between gestational age and the risk of SGA birth was assessed using restricted cubic spline analysis. Binary logistic regression models were used to assess the associations between single or combined maternal complications and SGA birth within the very preterm, late preterm, and term groups. Results were reported as odds ratios (ORs) with 95% confidence intervals (CIs). Additionally, effect modification by gestational age was assessed by incorporating interaction terms into the regression models. Among the 46,829 women with singleton pregnancies, the mean maternal age was 31.7 years (SD, 3.8 years). Restricted cubic spline analysis revealed a significant nonlinear inverse association between gestational age and SGA risk, with the odds of SGA being higher at earlier gestational ages and gradually decreasing toward term. PE showed the strongest association with SGA across all gestational periods, particularly in the very preterm group. In contrast, GDM was associated with lower odds of SGA, although the co-occurrence of PE and GDM was associated with an increased risk of SGA. GH was associated with an increased risk of SGA in the very preterm group (OR = 2.430; 95% CI, 1.156–5.111) but not in the late preterm or term groups. Interaction analysis indicated that the association between maternal complications and SGA weakened with advancing gestational age, with substantially weaker associations observed in term pregnancies. In contrast to GDM, PE and GH were associated with an increased risk of SGA, particularly in preterm pregnancies. These findings underscore the importance of early identification, close monitoring, and individualized management of women with PE or GH, particularly among pregnancies resulting in preterm birth.