Viral infections.

Although rubella is the only virus which can be regarded in the strict sense of the term a teratogen, there is no convincing evidence that other viruses can cause fetal damage of varying severity. The risk to the fetus appears to depend on the nature of the infectious agent, the maternal immune status and the gestational age when infection takes place. The possibility that subclinical maternal infections may cause damage must not be overlooked. As some of the viruses referred to can cause damage after the period of organogenesis, the use of the term 'teratogenic efect' in relation to viral infections is considered to be inappropriate.