During 2005, an estimated 92% of acquired immunodeficiency syndrome (AIDS) cases reported among children aged <13 years in the United States were attributed to mother-to-child transmission of human immunodeficiency virus (HIV) (CDC, unpublished data, 2006). Transmission can occur during pregnancy, labor, delivery, or breastfeeding. Estimates of the number of perinatal HIV infections peaked in 1991 at 1,650 and declined to an estimated range of 144-236 in 2002 (CDC, unpublished data, 2006). This reduction is attributed to routine HIV screening of pregnant women, use of antiretroviral (ARV) drugs for treatment and prophylaxis, avoidance of breastfeeding, and use of elective cesarean delivery when appropriate. With these interventions, rates of HIV transmission during pregnancy, labor, or delivery from mothers infected with HIV have been reduced to less than 2%, compared with transmission rates of 25%-30% with no interventions.