The relationship between hemoglobin concentration in the third-trimester and gestational age, birth weight of newborns: stratified analysis based on maternal age

This study retrospectively analyzed the association between hemoglobin concentration in the third trimester of pregnancy and neonatal gestational age and birth weight, and further explored whether there were differential effects between advanced maternal age and women of reproductive age.

Based on the Electronic Medical Record database of Gansu Provincial Maternity and Child-care Hospital, the clinical data of all singleton pregnant women who were registered and underwent prenatal check-ups at the hospital from January 1, 2020 to December 31, 2024 were collected. After screening according to the inclusion and exclusion criteria, a total of 31,690 pregnant women were ultimately enrolled in this study. Multivariable logistic regression was used to analyze the effect of third-trimester hemoglobin concentration on neonatal gestational age and birth weight. A restricted cubic spline (RCS) function with five knots was applied to analyze the association between changes in third-trimester hemoglobin concentration and neonatal birth weight outcomes.

A total of 31,690 pregnant women were included, among whom 4,664 (14.7%) were of advanced age and 27,026 (85.3%) were of childbearing. Third-trimester hemoglobin concentration exhibited an inverted U-shaped relationship with neonatal birth weight. In the advanced-age pregnant women, multivariable analysis revealed that, compared with a hemoglobin level of 110-119 g/L, a level ≤109 g/L significantly increased the risk of low birth weight and preterm birth, with the highest risk observed at <100 g/L. Meanwhile, the risk of preterm birth significantly increased at hemoglobin levels ≥140 g/L. In the women of reproductive age, compared with a hemoglobin concentration of 110-119 g/L, concentrations≥ 120 g/L were risk factors for low birth weight and preterm birth.

Third-trimester hemoglobin level is closely associated with adverse birth outcomes. Management strategies should consider maternal age stratification, with emphasis on early screening, dynamic monitoring, and rational iron supplementation to reduce the risk of adverse birth outcomes.