Maternal low-level lead exposure and fetal growth.

BACKGROUND: Limited epidemiologic studies have examined the association between maternal low-level lead exposure [blood lead (PbB) < 10 µg/dL] and fetal growth. OBJECTIVE: We examined whether maternal low-level lead exposure is associated with decreased fetal growth. METHODS: We linked New York State Heavy Metals Registry records of women who had PbB measurements with birth certificates to identify 43,288 mother-infant pairs in upstate New York in a retrospective cohort study from 2003 through 2005. We used multiple linear regression with fractional polynomials and logistic regression to relate birth weight, preterm delivery, and small for gestational age to PbB levels, adjusting for potential confounders. We used a closed-test procedure to identify the best fractional polynomials for PbB among 44 combinations. RESULTS: We found a statistically significant association between PbB (square root transformed) and birth weight. Relative to 0 µg/dL, PbBs of 5 and 10 µg/dL were associated with an average of 61-g and 87-g decrease in birth weight, respectively. The adjusted odds ratio for PbBs between 3.1 and 9.9 µg/dL (highest quartile) was 1.04 [95% confidence interval (CI), 0.89-1.22] for preterm delivery and 1.07 (95% CI, 0.93-1.23) for small for gestational age, relative to PbBs ≤ 1 µg/dL (lowest quartile). No clear dose-response trends were evident when all of the quartiles were assessed. CONCLUSIONS: Low-level PbB was associated with a small risk of decreased birth weight with a supralinear dose-response relationship, but was not related to preterm birth or small for gestational age. The results have important implications regarding maternal PbB.