Prenatal factors including fetal alcohol syndrome.

The first discovered exogenous teratogen causing mental retardation was rubella embryopathy described in 1940. Later, cytomegalic virus infection and toxoplasmosis during pregnancy and ionogenic radiation has been shown to cause embryofetopathies with concomitant mental retardation. Methyl mercury in high doses cause severe central nervous system pathology in both mothers and their fetuses. The fetal alcohol syndrome is now generally accepted as causing mostly mild mental retardation. Of therapeutic drugs, antiepileptics have been shown to carry a risk for the fetal antiepileptic syndrome complex. We have recently been able to describe fetal pathology following high intake of benzodiazepines during pregnancy.