A great deal of progress has been made in our understanding of mother-to-child transmission of HIV-1. Standardization of case definitions and transmission rate calculation methodologies, and a broader array of diagnostic options for detection of infant HIV-1 infection, will enhance our ability to evaluate and compare cohorts worldwide. In the next decade, several intervention studies should be completed. Carefully designed intervention studies have the potential both to determine which interventions are effective as well as to add to our understanding of vertical transmission of HIV-1. Regional differences in vertical transmission rates reflect a variety of viral, host, and obstetric factors. Intervention strategies will probably need to be regionally designed, taking into consideration these factors. Further research on timing and correlates of vertical transmission is necessary to determine the extent to which specific clinical trials can be extrapolated to public health policy.
PIP: Research related to maternal-child transmission of human immunodeficiency virus (HIV) has been advanced by standardization of case definitions and transmission rate calculation methodologies as well as enhanced diagnostic options for detecting infant HIV-1 infection. Standardization guidelines have yielded vertical transmission rate estimates of 25-30% in developing countries and 14-25% in developed countries. Mathematical modeling suggests that 95% of infant infections occur later than the last 2 months before delivery. Serial polymerase chain reaction evaluation has identified a 7.7% risk of in utero transmission, a 17.6% risk of combined in utero and intrapartum transmission, and a 4.9% incidence of late postnatal transmission. The risk of transmission through breast feeding has been estimated at 14%, with increases with longer durations. Advanced maternal clinical HIV status, primary infection, decreased maternal cell-mediated immunity, placentitis, ascending genital infection during the peripartum period, and syncytium-inducing HIV-1 strains have been associated with higher rates of maternal-child transmission. Prematurity, lack of cellular immunity, and vitamin A deficiency may be infant risk factors. The finding in an AIDS Clinical Trial Group that zidovudine (AZT) treatment was associated with a 67.5% reduction in risk has prompted widespread use of this regimen in developed countries; however, AZT is expensive and logistically difficult to administer in most developing country contexts. Randomized clinical trials currently underway are assessing the benefits of cesarean section delivery, postpartum HIV-specific immunoglobulin administration to infants, avoidance of breast feeding or early weaning, and antenatal maternal vitamin A administration. Selected intervention strategies should be regionally designed to take into account variations in viral, host, and obstetric factors.