The purpose of this study is to see if it is safe to give saquinavir-SGC (SQV) combined with low-dose ritonavir (RTV) plus zidovudine (ZDV) and lamivudine (3TC) to HIV-positive pregnant women and to see if it is safe to give 3TC and ZDV to their newborns. Another purpose is to see what levels of SQV, low-dose RTV, ZDV, and 3TC are found in mothers and what levels of ZDV and 3TC are seen in newborns. Another purpose of this study is to see whether SQV passes from mother to newborn and if it passes at a level that is safe for the newborn.