Perinatal infections.

Information concerning the most recently discovered infections with perinatal implications is constantly expanding. Hepatitis C virus is responsible for the majority of cases of sporadic and transfusion-related non-A, non-B hepatitis. Its prevalence in the general obstetric population is approximately 2%, but it is much higher in intravenous drug users and recipients of blood transfusions. The risk of vertical transmission is probably small (approximately 4.5%), but mothers coinfected with hepatitis C virus and human immunodeficiency virus type 1 are at higher risk of transmitting infection, possibly as a result of higher levels of viremia. Parvovirus B19 infection can jeopardize the fetus in approximately 9% of cases, leading to profound anemia, followed by hydrops and death. B19 has not been proven to be teratogenic, but survivors have a greater risk of in utero growth retardation. Cytomegalovirus remains the most common cause of congenital infections, and the fetal effects of primary maternal infection during gestation can be devastating. Recurrent infections carry a much lower risk of vertical transmission. Prenatal diagnosis is feasible and reliable. The factors affecting the vertical transmission of human immunodeficiency virus type 1 have been further delineated, and new avenues of research have been opened.