During the antepartum period, mothers receive SQV with [AS PER AMENDMENT 08/15/00: low-dose RTV plus] ZDV and 3TC. At onset of active labor, mothers receive loading doses of each of the study drugs, then receive study drugs for 12 weeks postpartum on the same schedule as during the antenatal period. Within 12 hours of delivery, infants begin receiving 3TC and ZDV and continue until 6 weeks of age. Mothers are followed until 12 weeks postpartum and babies are followed until 6 months of age. [AS PER AMENDMENT 02/09/99: For maternal dosing, 1 Combivir tablet (containing 3TC and ZDV) may be administered in place of the individual agents 3TC and ZDV. Patients who prematurely discontinue study treatment should continue to be followed for the duration of the study.]