Objective: To determine whether exposure to polychlorinated biphenyls (PCBs) or dichlorodiphenyl dichloroethene (DDE), either transplacentally or through breast feeding, affected scores on the Bayley Scales of Infant Development at 6 or 12 months of age.
Design: Cohort followed from birth to 1 year of age.
Setting: General community.
Participants: Volunteer sample of 858 infants, of whom 802 had Bayley scores available at either 6 months or 12 months or both.
Measurements and main results: Bayley scales and chemical measurements were done independently. Higher transplacental exposure to PCBs was associated with lower psychomotor scores at both 6 and 12 months of age; the difference between the mean scores in the lowest and highest PCB groups was 7 points at 6 months and 8 points at 12 months. Higher transplacental exposure to DDE was associated with higher mental scores at 6 months of age (the difference between the mean scores in the lowest and highest DDE groups was 6 points), but no relationship was seen at 12 months. Exposure to either chemical through breast feeding was apparently unrelated to Bayley scores.
Conclusions: Transplacental exposure to PCBs was associated with lower psychomotor scores. No deleterious effects were associated with breast feeding.