Perinatal transmission of the human immunodeficiency virus.

Vertical transmission of human immunodeficiency virus (HIV) from an infected mother to her fetus or infant can occur in utero and probably during labor and delivery. Transmission via breast milk has also been documented. Because of limitations of conventional HIV testing in infants, it is difficult to determine the rate of transmission from an infected mother to her fetus or infant, but it is probably between 20% and 60%, depending on the mother's health status. Perinatal HIV infection is a significant problem particularly in "Pattern II" countries, where HIV is spread primarily by heterosexual contact. In "Pattern I" countries, where HIV predominantly affects homosexual and bisexual men, children are infected by mothers who acquired the infection through I.V. drug abuse or sexual contact with an infected partner.