Maternal Anemia, Chorioamnionitis Together Raise Risk of Preterm Birth and Low Birth Weight: Study
China: Maternal anemia, particularly during late pregnancy, may significantly increase the likelihood of preterm birth and low birth weight, according to a new cohort study published in the World Journal of Pediatrics. Researchers also found that the presence of chorioamnionitis alongside anemia further amplified these risks.
The study was conducted by Wen Yu and colleagues from the Shanghai Key Lab of Reproduction and Development at Fudan University. The findings highlight the importance of monitoring maternal hemoglobin levels and preventing infections during pregnancy to improve neonatal outcomes.
Preterm birth and low birth weight remain major public health concerns worldwide, contributing substantially to infant illness and mortality. Previous research has identified maternal anemia as a risk factor for adverse pregnancy outcomes, but evidence regarding the combined impact of anemia and intrauterine infection has been limited. To address this gap, the researchers examined the relationship between maternal hemoglobin levels, chorioamnionitis, and birth outcomes in a large cohort of pregnant women.
For this purpose, the investigators conducted a retrospective cohort study involving 54,300 women who delivered at a university-affiliated hospital in Shanghai, China, between January 2018 and December 2023. Antenatal examination records were reviewed to assess maternal hemoglobin concentrations during pregnancy. The primary outcomes evaluated were preterm birth and low birth weight.
The study led to the following findings:
- Among the 54,300 pregnant women included in the study, 33.9% were diagnosed with anemia during pregnancy.
- A hemoglobin concentration below 100 g/L during the third trimester was significantly associated with an increased risk of adverse birth outcomes.
- Women with low hemoglobin levels in late pregnancy had an 87% higher risk of preterm birth (adjusted odds ratio [aOR] 1.87).
- Low third-trimester hemoglobin levels were also associated with a 45% greater risk of delivering a low-birth-weight infant (aOR 1.45).
- The coexistence of maternal anemia and chorioamnionitis further increased the likelihood of adverse birth outcomes.
- Pregnant women with both moderate-to-severe anemia and chorioamnionitis during the third trimester had more than three times higher odds of preterm birth (aOR 3.26).
- The combined presence of moderate-to-severe anemia and chorioamnionitis was also linked to a more than threefold increase in the odds of low birth weight (aOR 3.02).
The findings suggest that maternal anemia may impair fetal growth and shorten pregnancy duration, with concurrent chorioamnionitis further worsening these outcomes. The results highlight the importance of maintaining adequate hemoglobin levels and promptly detecting and treating infections during pregnancy.
The authors acknowledged that the retrospective, single-center design may limit generalizability and could be affected by missing data and residual confounding. Additionally, preterm birth was analyzed as an overall outcome, and the impact of some pregnancy-related conditions may not have been fully accounted for despite adjustments.
The researchers concluded that maternal anemia, particularly in the third trimester, is linked to an increased risk of preterm birth and low birth weight, with coexisting chorioamnionitis further amplifying these risks. They stressed that early identification and management of anemia and infections during pregnancy could help improve maternal and neonatal outcomes.
Reference:
Yu, W., Hao, YH., Chen, SY. et al. Association of maternal hemoglobin levels and chorioamnionitis with preterm birth and low birth weight: a cohort study. World J Pediatr (2026). https://doi.org/10.1007/s12519-026-01041-6
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