FETAL LEAD EXPOSURE AT EACH STAGE OF PREGNANCY AS A PREDICTOR OF INFANT MENTAL DEVELOPMENT

Abstract

ISEE-344 Introduction: There is concern that prenatal lead exposure may constitute a significant source of lead exposure to the developing fetus and infant. Little is known about the contribution of plasma lead to the toxic effects of lead but given the incomplete blood-brain barrier in their developing nervous systems, children may be more susceptible to insults during the prenatal periods. Prior research has relied primarily on umbilical cord or whole blood lead levels during pregnancy as biomarkers of fetal exposure. This study is aimed at evaluating maternal plasma lead, the biologically active fraction available to cross cell membranes, as a biological marker of fetal exposure to lead over the course of pregnancy. Methods: Measurements of whole blood and plasma lead, were obtained at each trimester of pregnancy. Infant neurocognitive development was assessed at 24 months of age using the Bayley Scales of Infant Development II Spanish (BSID II-S). The relationships between maternal plasma lead at each trimester during pregnancy and infant neurocognitive development were investigated among 103 subjects. Multiple linear regression modeling was used, with BSID-II MDI (Mental Development Index) as the outcome variable and log-e transformed plasma lead levels in the 1st trimester as the exposure. Results: Plasma-lead levels averaged 0.18, 0.17, 0.18 μg/L (SD=0.16, 0.31, 0.31) at each trimester of pregnancy, respectively. Whole blood-lead levels averaged 74.4, 66.0, 70.7 μg/L (SD=55.3, 51.1, 48.0), respectively. MDI scores averaged 93 (SD=12). Plasma lead concentrations in the first trimester of pregnancy (and not in the second nor third) were inversely associated with infant neurocognitive development at 24 months of age, as measured by poorer performance on the BSID II-S. After adjusting for plasma lead during the second and third trimester of pregnancy, sex, infant's nutritional status, child's concurrent blood lead at 24 months, maternal age and IQ, a 1 log-unit difference in maternal plasma lead during the first trimester of pregnancy was associated with a significant 6.9 point lower Mental Development Index (MDI) score at 24 months of age (p>0.01). A similar association was detected with whole blood lead, but it was not as strong as that with plasma lead. Discussion: The hazard period detected for both biomarkers was the first trimester of gestation. These findings suggest that the first trimester of pregnancy may be the hazard period of prenatal exposure to lead for the infant's mental development at 24 months of age.