Association between hemoglobin trajectories during pregnancy and birth outcomes: a retrospective cohort study based on latent growth mixture modeling analysis

Background/Objectives : Anemia in pregnancy is a global health problem with associated maternal and neonatal morbidity and mortality. This study aimed to investigate the association between hemoglobin trajectories during pregnancy and adverse neonatal outcomes. Methods : A retrospective cohort study was conducted using pregnancy records from Longquanyi District, Chengdu Maternity and Child Health Care Hospital ( from July 2024 and June 2025.) , involving 2,954 pregnant women with complete serial hemoglobin measurements. The outcome measures were preterm birth(PTB) and non-reassuring fetal status (NRFS). Latent growth mixture modeling was applied to identify distinct hemoglobin trajectories during pregnancy. Binary logistic regression was constructed to explore the association between hemoglobin trajectories and birth outcomes. Results : The incidence of anemia during pregnancy was 29.8% in 2954 pregnant women. Three distinct hemoglobin trajectories were identified: Traj-1 (high-rapid decline), Traj-2 (moderate-gradual decline), and Traj-3 (low-delayed recovery). Compared with the Traj-2 group, the Traj-1 (adjusted odds ratio (aOR) = 1.782, 95% confidence interval (CI) 1.145, 2.774) and Traj-3 (aOR = 2.048, 95% CI 1.082, 3.877) groups were positively associated with PTB. Moreover, the Traj-3 (aOR = 2.625, 95% CI 1.243, 5.544) groups exhibited an increased risk of NRFS. Conclusion: This study demonstrates that specific longitudinal hemoglobin trajectories, particularly high-rapid decline and low-delayed recovery patterns, exhibited an increased risk of PTB and NRFS, highlighting the clinical value of dynamic monitoring over single-point assessment in the practice of maternal and child health care.