Association of prenatal maternal blood lead levels with birth outcomes in the Japan Environment and Children's Study (JECS): a nationwide birth cohort study.

BACKGROUND Despite dramatic declines in prenatal maternal blood lead levels (BLLs) in most developed countries, little is known about the effects of extremely low-level (<1.0 µg/dL) lead exposure on fetal growth. METHODS We measured maternal BLL during the second or third trimester of pregnancy and assessed birth outcomes, including birthweight, preterm birth (<37 gestational weeks) risk, small for gestational age births (SGA; birthweight <10th percentile) and low birthweight (LBW; <2500 g). The association between birthweight and maternal BLL was estimated using linear and quadratic spline models. Multivariable logistic models were used to examine the risk of binary responses. RESULTS From 103 099 pregnant women, 20 000 blood samples were randomly selected for analysis. The maternal BLL range was 0.16-7.4 µg/dL, and the median was 0.63 µg/dL. After adjusting for covariates, the linear model showed that each 0.1 μg/dL increase in maternal BLL was associated with a 5.4 g decrease in mean birthweight [95% confidence interval (CI), 3.4 to 7.5 g]. The risk of SGA [adjusted odds ratio (aOR), 1.03; 95% CI, 1.02 to 1.05) and LBW (aOR, 1.03; 95% CI, 1.02 to 1.05) increased, whereas the risk of preterm delivery did not (aOR, 0.99; 95% CI, 0.97 to 1.02). CONCLUSIONS Even at a maternal BLL below 1.0 µg/dL, prenatal lead exposure was associated with decreased birthweight and increased risk of SGA and LBW, but not preterm delivery. The adverse effect estimates of prenatal lead exposure on birth outcomes were quantitatively small and clinically limited at this low level.