Maternal anemia and the risk of preterm birth: a meta-analysis

Globally, preterm birth continues to be a primary contributor to neonatal complications and fatalities. Anemia among the most common nutritional disorders in pregnancy has been proposed as a potential contributor to early delivery. Although extensively studied, the available evidence does not yet provide a clear consensus. This study aimed to conduct a meta-analysis to quantitatively assess the relationship between maternal anemia and the risk of preterm birth.

This meta-analysis was conducted and reported in accordance with the PRISMA guidelines and the MOOSE checklist. A systematic and exhaustive search was performed across multiple electronic databases PubMed, Scopus, Web of Science, Embase, and the Cochrane Library to identify relevant studies published from inception to 1 January 2025. Effect sizes were combined using a random-effects meta-analysis.

A total of 45 articles, reporting 60 independent study populations comprising 2,119,392 pregnant individuals were included. Considerable heterogeneity was found across the included studies (I² = 95.54%, p < 0.001), which justified the application of a random-effects model for pooling effect sizes. Maternal anemia was significantly associated with an increased risk of preterm birth (pooled odds ratio[OR] = 1.28, 95% confidence interval [CI]: 1.20-1.36, p < 0.001). Despite substantial heterogeneity, sensitivity analyses confirmed the robustness of this association. The relationship was strongest in studies conducted in Asia (OR = 1.30, 95% CI: 1.22-1.40; p < 0.001) and the Europe (OR = 1.24, 95% CI: 1.08-1.41; p = 0.001) and reached statistical significance when anemia was assessed during the first trimester (OR = 1.12, 95% CI: 1.03-1.51; p = 0.007) and the third trimester (OR = 1.65, 95% CI: 1.42-1.91; p < 0.001), while no significant associations were found in the second trimesters (OR = 1.10, 95% CI: 0.99-1.22; p = 0.05). Funnel plot asymmetry and a significant Egger's test (p = 0.001) indicated potential publication bias, although Begg's test was not significant (p = 0.425).

The current evidence suggests that maternal anemia, particularly in the third trimester, is significantly associated with an increased risk of preterm birth. These findings emphasize the clinical imperative for comprehensive and timely anemia screening during the third trimester. Integrating targeted interventions such as iron and micronutrient supplementation, is essential to mitigate the risk of preterm delivery and improve neonatal outcomes.