The effects of intrauterine infections with bovine viral diarrhea virus (BVDV) vary depending on the stage of gestation and the development of the fetal immune system. During the first trimester, infection may result in fetal death or birth of persistently infected calves immunotolerant to the virus. Thereafter, infections induce a variety of central nervous system and other malformations. Later stages of pregnancy show little susceptibility to infection and calves with precolostral antibodies to BVDV are born.