Antecedents and correlates of improved cognitive performance in children exposed in utero to low levels of lead.

Up to 2 years of age, children with umbilical cord blood lead levels of 10 to 25 micrograms/dL achieve significantly lower scores on tests of cognitive development than do children with lower prenatal exposures. By age 5 years, however, they appear to have recovered from, or at least compensated for, this early insult. Change in performance between 24 and 57 months of age was examined in relation to level of postnatal lead exposure and various sociodemographic factors. Among children with high prenatal lead exposure, greater recovery of function was associated with lower blood level at 57 months, higher socioeconomic status, higher Home Observation for Measurement of the Environment scores, higher maternal IQ, and female gender. The difference between the scores at 57 months of children with optimal and less optimal values on these variables generally exceed 1/2 standard deviation. Higher prenatal lead exposure is associated with an increased risk of early cognitive deficit. Furthermore, the risk that a deficit will persist through the preschool years is increased among children with high prenatal exposure and either high postnatal exposure or less optimal sociodemographic characteristics.