Meta-analysis of maternal exposure to heavy metals (lead, cadmium, mercury, chromium) and adverse pregnancy outcomes.

BACKGROUND: The association of heavy metal exposure with adverse pregnancy outcomes (APOs) remains a subject of debate. The goal of the present study was to analyze the correlation of heavy metals (lead [Pb], cadmium [Cd], mercury [Hg], chromium [Cr]) with APOs. METHODS: A systematic review was carried out across four databases: The Cochrane Library, PubMed, Web of Science, and Embase up to November 19, 2024. Two independent researchers performed the literature screening and data extraction based on predefined eligibility criteria. Then, based on the selected literature, the researchers extracted the odds ratios (ORs) and confidence intervals (CIs) of heavy metals (Pb, Cd, Hg, and Cr) and pregnancy outcomes (preterm birth, low birth weight [LBW], and small gestational age [SGA]). The Newcastle-Ottawa Scale (NOS) was adopted for quality assessment. Heterogeneity tests, sensitivity checks, subgroup evaluations, and publication bias analyses were implemented via Stata 15.1 software. RESULTS: This meta-analysis incorporated 24 studies, involving 52,390 subjects. The results demonstrated a significant association of Pb concentration with preterm birth (OR = 1.4, 95% CI: 1.17, 1.68; P < 0.001) and SGA (OR = 1.66, 95% CI: 1.04, 2.66; P = 0.034), though not with LBW. Cd concentration was associated with LBW (OR = 1.10, 95% CI: 1.00, 1.20; P = 0.041) and SGA (OR = 1.27, 95% CI: 1.08, 1.48; P = 0.003), but not with preterm birth. No significant association was observed between Hg concentration and preterm birth. Due to insufficient data, the impact of Cr was not analyzed. Subgroup analysis suggested that region, study design, measurement time, and measurement source may influence the conclusions. CONCLUSIONS: This meta-analysis indicated that Pb exposure was associated with elevated risks of both preterm birth and SGA. Cd exposure exhibited significant associations with LBW and SGA. However, the limited number of articles for other indicators warrants further investigation. Future prospective, high-quality studies are encouraged to explore these relationships further.