Pregnant women start with RTV (increasing gradually over a few days) plus 3TC plus ZDV until active labor. Intrapartum, women receive RTV plus 3TC plus ZDV, then postpartum (after cord clamped until 12 weeks postpartum), RTV plus 3TC plus ZDV. [AS PER AMENDMENT 2/9/99: For maternal dosing, one Combivir tablet (containing 3TC and ZDV) may be administered in place of the individual agents 3TC and ZDV. During the intrapartum period, Combivir is held and the patient follows intrapartum 3TC/ZDV dosing. During the intrapartum period, no RTV is given after the onset of active labor. During the postpartum period, RTV is begun as soon as oral intake is allowable following delivery. During the postpartum period, Combivir may be resumed. All subjects who prematurely discontinue study treatment should continue to be followed for the duration of the study.] [AS PER AMENDMENT 9/28/99: During the intrapartum period, RTV is given at the start of active labor.] Infants begin 3TC and ZDV as soon as oral intake is tolerated. Infants participate in one of two cohorts. The first four infants delivered (Cohort 1) receive RTV as a single dose between Days 8 and 12. The next six infants delivered (Cohort 2) start RTV at 2-3 days of life. The dosing schedule is based on Cohort 1 drug pharmacokinetics data. [AS PER AMENDMENT 2/9/99: Cohort 1 is expanded to seven mother/infant pairs.] [AS PER AMENDMENT 9/28/99: Cohort 1 is expanded to eight mother/infant pairs.] Both maternal and infant blood is drawn to assess drug pharmacokinetics. Cervical secretions are collected to assess presence of virus. In addition, all placentas are examined by histopathology to determine the role of placenta on preterm delivery in women receiving combination antiretroviral therapy.