Part 1: To determine both the safety, tolerance, and pharmacokinetic profile (blood levels) of recombinant CD4 immunoglobulin G (rCD4-IgG) by intravenous bolus administration (given through the vein) in women with HIV infection who are in their third trimester (last three months of pregnancy). To determine the safety of maternal/fetal transfer of rCD4-IgG in infants born to mothers entered into the study. To obtain a preliminary indication of the antiviral and immunologic effects of rCD4-IgG in HIV seropositive pregnant women and their newborns.