Human immunodeficiency virus (HIV) is a retrovirus that can cause life-threatening opportunistic infections, malignancies, and can eventually lead to acquired immunodeficiency syndrome (AIDS) and death when untreated. HIV can be transmitted through bodily fluids, such as blood, semen, vaginal fluid, and breast milk. The transmission of HIV from mother to child in pregnancy has been of paramount concern for the past three decades with recent medical advancements leading to a low rate of perinatal transmission.
Epidemiology of HIV in Pregnancy
Perinatal infection is the most common route of HIV infection in children. The risk of this transmission has decreased from 25% without intervention to <2% with currently available medical treatments in developing countries.1 In the past two decades, routine HIV testing in pregnancy and appropriate intervention have led to more than a 90% decline in mother-to-child transmission (MTCT) in the United States (Figures 16-1 and 16-2). The Center for Disease Control (CDC) estimates that 1,144,500 persons older than 13 years of age are living with HIV infection, including 180,900 (15.8%) that are unaware of their infection. In 2010, an estimated 217 children younger than 13 years of age were diagnosed with HIV; 162 (75%) of those children were perinatally infected.2 The prevalence of HIV infection in prenatal clinics in the United States ranges from 0.13% to 5%.3,4,5 Because of early detection and intervention of HIV in pregnancy, less than 100 new cases of AIDS per year are diagnosed in the United States (Figure 16-1).
Number of cases of perinatal infection leading to AIDS in the United States, 1985-2011. Used with permission from the Centers for Disease Control and Prevention.
Rates of perinatally acquired HIV infections by race from 2007 to 2009. From the Centers for Disease Control and Prevention.
Pregnancy and Risks of Transmission
Although the rate of transmission has declined in recent years, there are several risks factors that impact MTCT. Without medical intervention, about two-thirds of MTCT occur during labor and delivery and one-third occurs in utero (Figure 16-3). In utero transmission mostly occurs during the third trimester of pregnancy. Breastfeeding also poses a significant risk of transmission of HIV. The most important predictor of perinatal transmission appears to be plasma HIV RNA load. Transmission can occur at any viral load but usually does not occur with viral loads <1000 copies/mL. Although the risk of transmission increases with increasing viral loads, there is no clear threshold above which all women transmit the virus.6 Other risk factors that contribute to MTCT include obstetrical complications such as prolonged and premature rupture of membranes, mode of delivery, and concomitant genital tract infections. Also neonatal low birth weight, cigarette smoke exposure, maternal substance abuse, and unprotected sex with multiple partners may pose a risk for increased transmission.7,8,9,10