Association of maternal hemoglobin levels and chorioamnionitis with preterm birth and low birth weight: a cohort study

Background Approximately one-quarter of infants worldwide are born either preterm, with a low birth weight, or both. Maternal anemia significantly increases the risk of adverse birth outcomes. We aimed to investigate the association between hemoglobin levels—alone and in conjunction with chorioamnionitis—and birth outcomes. Methods This retrospective cohort study included 54,300 pregnant women who delivered between January 2018 and December 2023 and whose antenatal examination records were available at a university-affiliated hospital in Shanghai, China. The primary outcomes were preterm birth and low birth weight. Results In our cohort, 33.9% of mothers were diagnosed with anemia. A low hemoglobin concentration (hemoglobin concentration < 100 g/L) during the third trimester was significantly associated with an increased risk of preterm birth [adjusted odds ratio (aOR) = 1.87; 95% confidence interval (CI) = 1.56–2.24] and low birth weight (aOR = 1.45; 95% CI = 1.20–1.76). Notably, the co-occurrence of moderate to severe anemia and chorioamnionitis was associated with higher odds of preterm birth and low birth weight in the third trimester, with aORs (95% CI) of 3.26 (1.92–5.52) and 3.02 (1.78–5.11), respectively. Conclusions Maternal anemia, particularly during the third trimester, is associated with an increased risk of preterm birth and low birth weight. The co-occurrence of anemia and chorioamnionitis further amplifies these risks.