Patients participating in the A5153s substudy receive either NFV or LPV/r as part of their HAART. Pharmacokinetic blood sampling takes place at 36 weeks gestation, 6 weeks postpartum, and 24 weeks postpartum. Patients record the administration times and doses of their NFV or LPV/r for 48 hours prior to each substudy visit, and hold their regularly scheduled doses of antiretroviral medications on substudy days. Patients arrive at the clinic fasting (no food or drink for the previous 8 hours) and are given a standardized breakfast prior to supervised administration of their NFV or LPV/r dose. An intravenous catheter is placed in an arm vein for blood collection at pre-dose and 1, 2, 4, and 6 hours post-dose.