Background: Prenatal exposure to anticonvulsant drugs may influence the developing brain of the fetus.

Study design: Head size at birth was studied retrospectively, cognitive functioning in adulthood was studied in a follow-up study.

Setting: University hospital.

Subjects: Retrospective study: 198 exposed subjects and 198 matched control subjects. Follow-up study: 147 exposed and 147 matched control subjects. Control subjects were matched with respect to age, sex and their mothers' ages.

Measurements: Head size at birth, educational level and score on psychological tests.

Results: At birth, phenobarbital plus diphantoin-exposed infants had a significant smaller FOC compared to phenobarbital-exposed and control infants. Results on educational level showed that 12% of the exposed subjects but only 1% of the control subjects had attended specialized schools for children with learning problems (p=.003); on psychological tests these subjects had significant lower scores compared to their control subjects. The remaining group of anticonvulsant-exposed subjects obtained similar scores on psychological tests compared to their control subjects. No relationships between between small head size at birth, family climate or socio-economic status and learning problems were found.

Conclusion: Prenatal exposure to phenobarbital and hydantoin probably only affect intellectual abilities in subjects who are susceptible to this functional teratogenic influence.