Low level lead exposure in the prenatal and early preschool periods: intelligence prior to school entry.

The hypothesis that low level lead exposure in the fetal and early preschool years is related to neuropsychological deficit is being examined in a prospective study of development through the preschool years. Clear and consistent support for the hypothesis was not obtained in previously reported findings relating maternal and cord blood lead level (PbB) and PbB from venous samples through age three years to a series of developmental tests. It was concluded the relationship of lead level and cognitive development was primarily a function of the dependence of each on the quality of the caretaking environment. The cohort has now been examined at age four years, ten months, an age selected to assess development just prior to school age. The test used was the Wechsler Preschool and Primary Scale of Intelligence. We found statistically significant correlations between most of the PbB measures and the intelligence test scores, but these were attenuated, not statistically significant and not consistent in direction when relevant confounding variables were considered. Possible biases or threats to validity were reviewed. Effect sizes relating both prenatal and preschool lead exposure to intellectual development were small, not statistically significant, and not consistent in direction.