Vertical transmission of viral infections.

A variety of congenital viral infections are responsible for a large proportion of the mortality and morbidity in infancy and childhood. Vertical transmission may occur during primary maternal infection or during chronic or recurrent infection, with different implications for counselling and testing in pregnancy. Strategies for the diagnosis and prevention of mother-to-child transmission differ according to the timing and mechanisms involved. As demonstrated by hepatitis B research in the past and human immunodeficiency virus today, multicenter cohort studies and clinical trials are a key to developing effective interventions.