The majority of perinatally infected infants are infected during the labor and delivery process, but recent studies suggest that additional factors, such as postexposure prophylaxis, are likely to be involved in the prevention of MTCT of HIV. It is possible that antiretroviral dosing only during labor and short-term dosing to newly born infants would be sufficiently effective to prevent MTCT of HIV. TDF is a nucleoside reverse transcriptase inhibitor that has demonstrated significant effectiveness in preventing MTCT of simian immunodeficiency virus (SIV) in a primate model of HIV. FTC/TDF is a combination of two NRTIs being studied because this combination has the potential to prevent MTCT, while protecting the mother from developing resistance that may develop with single drug therapy. This study will evaluate the safety, tolerance, and pharmacokinetics (PK) of single doses of TDF and FTC/TDF in both HIV infected pregnant women and their newborn infants.