Abstract:

Objective Both preterm and postterm pregnancies can adversely affect neonatal outcomes; however, research on the differences in neonatal outcomes across various gestational ages within the full-term range (37⁺⁰ to 41⁺⁶ weeks) remains limited. Therefore, this study aims to explore the potential association between the gestational week of delivery within full-term pregnancy and adverse perinatal outcomes using a retrospective pregnancy cohort from a single center. Methods A retrospective cohort of pregnant women who delivered at hospital between January 2023 and December 2024, and their neonates, was included. Maternal and neonatal characteristics, as well as adverse outcomes [including large for gestational age (LGA), small for gestational age (SGA), low birth weight (LBW), macrosomia, 5-minute Apgar score≤7, and stillbirth], were compared across different gestational weeks. Restricted cubic spline (RCS) models and multivariable logistic regression were employed to analyze the association between gestational week at delivery and adverse perinatal outcomes. Results A total of 13,123 singleton full-term natural delivery cases were included from 43,502 parturients. They were included and categorized into five groups according to gestational week at delivery: the 37⁺⁰-37⁺⁶ weeks group (n=952), the 38⁺⁰-38⁺⁶ weeks group (n=2,707), the 39⁺⁰-39⁺⁶ weeks group (n=4,920), the 40⁺⁰-40⁺⁶ weeks group (n=4,164), and the 41⁺⁰-41⁺⁶ weeks group (n=380). The proportion of advanced maternal age (≥35 years) decreased with increasing gestational age, declining from 18.2% in the 37⁺⁰-37⁺⁶ weeks group to 10.0% in the 41⁺⁰-41⁺⁶ weeks group. The distribution of pre-pregnancy BMI categories differed significantly among the gestational age groups (P<0.001), with the 37⁺⁰-37⁺⁶ weeks group having higher proportions of overweight and obesity (10.7% and 1.7%, respectively). Gestational weight gain also varied significantly across groups (P<0.001), with the 41⁺⁰-41⁺⁶ weeks group exhibiting greater weight gain during pregnancy. The incidence of gestational diabetes mellitus (GDM) and hypertensive disorders of pregnancy/preeclampsia differed significantly among gestational age groups (P<0.001), both being most prevalent in the 37⁺⁰-37⁺⁶ weeks group (27.2% and 4.3%, respectively). There were 15 stillbirths (0.1%), 13,108 surviving newborns, among whom 423 newborns (3.2%) were LGA, 799 (6.1%) were SGA, 166 (1.3%) were macrosomia, 180 (1.4%) were LBW, and 9 (0.1%) had a low Apgar score at 5 minutes. Restricted cubic spline analysis initially suggested that 39⁺⁰-40⁺⁶ weeks of gestation might represent a window of lower risk for adverse neonatal outcomes. Multivariate logistic regression further confirmed that, compared with delivery at 39⁺⁰-39⁺⁶ weeks, delivery at 37⁺⁰-37⁺⁶ weeks and 38⁺⁰-38⁺⁶ weeks was associated with a significantly increased risk of SGA (P<0.01); delivery at 40⁺⁰-40⁺⁶ weeks and 41⁺⁰-41⁺⁶ weeks was associated with a significantly increased risk of macrosomia (P<0.001); delivery at 37⁺⁰-37⁺⁶ weeks and 38⁺⁰-38⁺⁶ weeks was associated with a significantly increased risk of LBW (P<0.001); the 41⁺⁰-41⁺⁶ weeks group had an increased risk of a 5-minute Apgar score≤7 (P=0.029); and delivery at 37⁺⁰-37⁺⁶ weeks and 38⁺⁰-38⁺⁶ weeks was associated with a significantly increased risk of stillbirth (P<0.01). Conclusions The timing of delivery in full-term pregnancies may affect neonatal outcomes. The period from 39⁺⁰ to 40⁺⁶ weeks of gestation is a window during which the risks of various adverse outcomes are at relatively low levels. This study may have potential value for further optimizing clinical pregnancy monitoring and perinatal management.

Key words: full-term pregnancy, gestational weeks, poor perinatal outcome, newborn