The etiology of autism: pre-, peri- and neonatal factors.

OBJECTIVE

To examine pre-, peri-, and neonatal factors in autism using composite optimality scores.

METHOD

Pre-, peri-, and neonatal composite optimality scores were examined in 39 autistic subjects and 39 randomly matched sibling controls using a modification of the Gillberg Optimality Scale (Modified-GOS). Scores were based on best-estimate ratings of maternal interviews and medical records. Rules for best-estimate ratings were derived from a study of agreement between these two sources.

RESULTS

Significant differences in optimality between autistic probands and their siblings were not present after adjustment for "maternal parity." Examination of specific variables revealed that only maternal parity differed significantly between autistic subjects and randomly matched sibling controls, reflecting an excess of first and fourth born among the autistic subjects.

CONCLUSION

The findings of this study suggest that previous reports of an association between optimality and autism are a result of failure to adjust for birth order.