Maternal Hemoglobin Concentrations in Early and Late Pregnancy and Adverse Birth Outcomes: A Nationwide Cohort Study in Sri Lanka.

Abstract

Background: Maternal hemoglobin (Hb) plays a critical role in pregnancy and may influence birth outcomes.

Objectives: The study aimed to examine associations between maternal Hb in early and late pregnancy and adverse birth outcomes in a cohort of singleton pregnancies in Sri Lanka.

Methods: This prospective study analyzed 1315 mother-newborn pairs. Anemia was defined as Hb < 11.0 g/dL, based on World Health Organization cutoffs for the first and third trimesters, corresponding to the early and late pregnancy time points studied. Outcomes included preterm birth, low birth weight (LBW), and small-for-gestational age (SGA). Multivariate logistic regression and restricted cubic spline analyses were used to assess associations, adjusting for maternal age, prepregnancy body mass index, parity, and history of pregnancy loss. LBW models were evaluated with and without adjustment for gestational age.

Results: Median Hb was 12.0 g/dL (interquartile range [IQR]: 11.4-12.7) in early pregnancy and 11.4 g/dL (IQR: 10.8-12.0) in late pregnancy. Anemia prevalence increased from 16% to 32%, with a notable shift of women from the 11.0 to 12.9 g/dL category into the anemic range. Early-pregnancy Hb 9.0-10.9 g/dL was associated with higher odds of preterm birth [adjusted odds ratio (aOR): 2.18; 95% confidence interval (CI): 1.42, 3.34], whereas Hb ≥ 13.0 g/dL showed a nonsignificant increase (aOR: 1.49; 95% CI: 0.97, 2.30). In late pregnancy, Hb ≥ 13.0 g/dL was associated with increased odds of LBW (aOR: 2.18; 95% CI: 1.04, 4.54) in models without gestational age adjustment. No significant associations were observed for SGA. Restricted cubic spline analysis showed a significant U-shaped association between early-pregnancy Hb and preterm birth, with the lowest odds at 11.0-12.9 g/dL.

Conclusions: Low and high maternal Hb concentrations were associated with increased odds of adverse birth outcomes. These findings support careful monitoring of maternal Hb during pregnancy and further research to define an upper limit for Hb in pregnancy.