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.