• Proportion of women in each randomized arm who have one or more new NVP resistance mutations as identified by consensus sequencing or oligonucleotide ligation assay (OLA) in plasma [ Time Frame: at Days 10, 21, or 30 or Weeks 5, 6, or 8 postpartum ] [ Designated as safety issue: No ]
  
• proportion of women in the historical control group and each randomized arm who have one or more new NVP resistance mutations as identified by consensus sequencing or OLA in plasma [ Time Frame: at Day 10 or Week 6 postpartum ] [ Designated as safety issue: No ]
  
• pharmacokinetic parameters as described in the Pharmacology Plan as specified by the protocol [ Time Frame: Throughout study ] [ Designated as safety issue: No ]
  

A single dose of nevirapine (NVP) given to an HIV infected pregnant woman in labor followed by a single dose to her infant has been shown to be a simple and effective means of reducing mother-to-child transmission (MTCT) of HIV among women who have not received ART during pregnancy. However, development of NVP- and other nonnucleoside reverse transcriptase inhibitor (NNRTI)-resistant virus is a concern. An optimal ART regimen that can prevent selection of resistant virus while efficiently preventing MTCT is needed. This study will evaluate 3 different ART strategies for preventing the development of NVP resistance in HIV infected pregnant women. NVP and LPV/r pharmacokinetics (PK) will also be evaluated in this study.

Participants will be randomly assigned to one of three study arms. All study participants will receive a single dose of oral NVP at the onset of labor, oral zidovudine (ZDV) at the onset of labor, and oral ZDV every three hours during labor. Arm A participants will receive enteric-coated didanosine (ddI) and LPV/r orally twice daily beginning at the onset of labor and continuing through 7 days postpartum; oral ZDV will also be taken twice daily for 7 days postpartum. Arm B participants will receive enteric-coated ddI beginning at the onset of labor and continuing through 30 days postpartum; oral ZDV will also be taken twice daily for 30 days postpartum. Arm C participants will receive enteric-coated ddI and LPV/r orally twice daily beginning at the onset of labor and continuing through 30 days postpartum; oral ZDV will also be taken twice daily for 30 days postpartum.

All women will be followed for at least 24 weeks postpartum. Women with resistance mutations identified within 8 weeks postpartum will be followed until 72 weeks postpartum. Infants will be followed until at least 12 weeks of age. There will be 11 study visits for women. Medical history assessment, a physical exam, and blood collection will occur at all visits. Blood collection for PK studies will occur at Days 10, 21, and 30. All women will be asked to complete an adherence questionnaire at Day 10; women assigned to Arms A and B will also be asked to complete an adherence questionnaire at Day 30. There will be 6 study visits for infants. Medical history assessment and a physical exam will occur at most visits; blood collection will occur at all visits.