How does cmv affect the unborn baby during pregnancy?

Depends.: If the mother has been previously exposed, then the fetus is protected by her antibodies and should not suffer when the mother is exposed to CMV during pregnancy. If the pregnant woman has never before been infected with cmv, the fetus is at risk for in utero infection that can range from lethal to mild/none. The earlier the infection the more severe and unlikely; the later, the milder and likely.