Early sensory-motor development and prenatal exposure to lead.

As part of a longitudinal study of the early developmental effects of exposure to lead, we administered the Bayley Scales of Infant Development at age 6 months to infants classified into three groups based on their umbilical cord blood lead levels ("low": mean = 1.8 micrograms/dl; "mid": mean = 6.5 micrograms/dl; "high": mean = 14.6 micrograms/dl). No infant had a cord blood lead level greater than 30 micrograms/dl, the level currently regarded as the upper limit of "normal" for young children. Multiple regression analyses indicated that high cord blood levels were associated with lower covariance-adjusted scores on the Mental Development Index. Scores on the Psychomotor Development Index were not significantly related to cord blood lead level. The level of lead in blood at 6 months of age was not associated with scores on either the Mental or Psychomotor Development Index. These data are compatible with the hypothesis that low levels of lead delivered transplacentally are toxic to infants.