Path analysis of prenatal mercury levels and birth weights in Korean and Taiwanese birth cohorts

Prospective cohort studies of the effect of mercury (Hg) exposure on birth weight have shown conflicting results. We combined data from Taiwanese and Korean birth cohorts, and assessed the effects of Hg exposure on birth weight. The first cohort was drawn from the Mothers and Children's Environmental Health (MOCEH) study performed in Korea from 2006 to 2010. The second cohort was enrolled from 2004 to 2005 and included singleton term births from the Taiwan Birth Panel Study (TBPS). In total, 1147 pregnant women were included in this study. A pooled analysis was performed to obtain combined estimates of the association between prenatal total Hg exposure and birth weight. A significant negative association between maternal and cord blood Hg and birth weight in the high-Hg group (Hg level > 25th percentile) was detected (maternal blood: β = − 0.056; 95% CI, − 0.100 to − 0.013, cord blood: β = − 0.075; 95% CI, − 0.121 to − 0.028). Hg level showed a negative coefficient in the path analysis, indicating an adverse effect on birth weight (total effects: β = − 0.177, P = 0.01 in MOCEH, β = − 0.204, P = 0.03 in TBPS), but fish consumption exhibited a strong positive coefficient. In addition, fish consumption exerted a significant indirect effect on birth weight through exposure to cord blood Hg. Exposure to hazardous contaminants and beneficial nutrients may be highly correlated in those who frequently consume fish. Moreover, Hg in cord blood may adversely affect birth weight.