Association between maternal exposure to mercury during pregnancy and birth weight: a systematic review and...

Epidemiological research has suggested that exposure to mercury in pregnancy may negatively affect birth weight (BW). However, the results were inconclusive. This meta-analysis aimed to provide a quantitative summary of evidence for the relation of prenatal mercury exposure to BW.

We performed a systematic search in the PubMed and Scopus databases until March 2024. The pooled effects of prenatal mercury exposure on birth weight (BW) were assessed using a random-effects model, using the standardized regression coefficients (β) along with their corresponding 95% confidence intervals (CI). Stratified analysis by type of specimen, sample size, method of mercury assessment, Hg concentration, and trimester of sampling was conducted to investigate possible sources of heterogeneity.

Forty-one studies, including 128,487 participants, were analyzed. In the overall analysis, no significant relationship was revealed between prenatal mercury exposure and BW (β= -0.002, 95%CI: -0.003 to 0.0001; P = 0.06) with substantial heterogeneity (I² = 63.0, P = 0.001). However, in the stratified analysis, exposure to mercury was inversely linked to the neonatal BW in studies on placental exposure (β= -0.144, 95%CI: -0.272 to -0.016; P = 0.02) and exposure at delivery (β= -0.010, 95%CI: -0.020 to -0.002; P = 0.01) and at the third trimester (β= -0.0003, 95%CI: -0.0005 to -0.0001; P = 0.004) of pregnancy. Mercury was also negatively associated with BW in studies that measured mercury using atomic absorption spectroscopy (β= -0.010, 95%CI: -0.020 to -0.001; P = 0.02). Furthermore, blood Hg levels ≥ 2.09 µg/L (β = -0.029, 95% CI: -0.052 to -0.006; P = 0.01) and placental Hg levels ≥ 10 µg/kg (β = -0.193, 95% CI: -0.293 to -0.094; P = 0.001) were significantly associated with lower BW.

This meta-analysis revealed that mercury exposure may be negatively associated with birth weight, especially when higher concentrations are present in the blood and placenta, as well as during the late stages of pregnancy, which significantly correlates with lower neonatal BW.