AMENDED: In Part 2 of the study, a total of nine pregnant women are enrolled in Groups C, D, and E and receive a higher dose of rCD4-IgG at the onset of labor. If the mother has not delivered 18 hours after rCD4-IgG injection, a second injection at the same dose is administered; daily injections are given thereafter until delivery. The newborns receive 1 of 3 doses of rCD4-IgG daily for the first 5 days of life. Infants are enrolled sequentially to each dose level.