Association of prenatal phenobarbital and phenytoin exposure with small head size at birth and with learning problems

Small head size has been observed in prenatally anticonvulsant-exposed neonates. In infancy, cognitive impairments were revealed. It is presently unknown whether these impairments are permanent or disappear after puberty. We studied the link between the prenatal influence of anticonvulsants on brain development and cognitive functioning in adulthood: a retrospective study on head size and a follow-up assessing cognitive capacities among adults who had been included in the retrospective study. The retrospective study comprised 172 exposed and 168 control neonates, matched with respect to age, sex and their mothers' age. Prenatally phenobarbital + phenytoin-exposed neonates had a significantly smaller occipitofrontal circumference (OFC) than prenatally phenobarbital-monotherapy-exposed and control neonates (mean difference of 0.7 cm). In the follow-up, no difference in cognitive functioning was found between the exposed and the control groups. Most of the prenatally anticonvulsant-exposed subjects had normal intellectual capacity. However, 12% of the exposed subjects versus 1% of the controls had persistent learning problems. In addition, more of the exposed subjects were mentally retarded. There was no clear relationship between learning problems and small OFC, maternal epilepsy or unfavourable family climate.

We conclude that the combination of phenobarbital + phenytoin affects the fetal OFC. The smaller OFC does not seem to be related to cognitive functioning in adulthood, but learning problems and mental retardation proved to be more prevalent among exposed subjects. Phenobarbital and phenytoin may therefore affect cognitive capacity but only in infants who are susceptible to this particular influence of the drugs.