Background: The primary purpose of the study was to establish a possible association between very low levels of prenatal exposure to lead and mental development of children at 12, 24 and 36 months of age. Methods: The study sample consisted of 444 children born to mothers who attended ambulatory prenatal clinics in Krakow inner city in the first and second trimesters of pregnancy. We assessed exposure to lead by the cord blood lead measurements, and mental development in infancy and early childhood using the Bayley Mental Development Index (MDI). The relationship between prenatal lead exposure and MDI scores at each follow-up period was evaluated with linear multivariate regression. To test the overall effect of maternal exposure to lead during pregnancy on the Bayley test scores at 12, 24 and 36 months of age, we used the generalized estimating equations (GEE) longitudinal panel model as well. Results: The median lead level in cord blood was 1.23 μg/dl, in the range of 0.44–6.90 μg/dl. An adverse effect of prenatal lead exposure (log-transformed lead concentrations) on MDI scores at 12 months of age was of border significance (β = –5.42, 95% CI: –11.19 to 0.35). Subsequent testing of children at 24 months of age showed a significant inverse association of mental function and lead exposure (β = –7.65, 95% CI: –14.68 to –0.62). A significant deficit in cognitive function due to prenatal lead exposure was also confirmed at 36 months of age (β = –6.72, 95% CI: –12.5 to –0.89). The GEE panel model showed that the average deficit in the cognitive development attributable to lead exposure over 3 years was also significant (β = –6.62, 95% CI: –1.52 to –1.72). Mental function scores of girls were better than boys, and the effect of maternal education remained strongly significant in relation to mental function of 3-year-olds. Conclusion: The results of the study demonstrate that the neurotoxic impact of very low levels of prenatal lead exposure (below 5 μg/dl) may occur in infants and very young children, and suggest a revision of established health guidelines for prenatal lead exposure criteria.

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