BACKGROUND There have been no clinical trials in resource-rich regions that have addressed the question of which highly active antiretroviral therapy (HAART) regimens are more effective for optimal viral response in antiretroviral-naive, human immunodeficiency virus (HIV)-infected pregnant women. METHODS Data on 240 HIV-1-infected women starting HAART during pregnancy who were enrolled in the prospective European Collaborative Study from 1997 through 2004 were analyzed. An interval-censored survival model was used to assess whether factors, including type of HAART regimen, race, region of birth, and baseline immunological and virological status, were associated with the duration of time necessary to suppress viral load below undetectable levels before delivery of a newborn. RESULTS Protease inhibitor-based HAART was initiated in 156 women (65%), 125 (80%) of whom received nelfinavir, and a nevirapine-based regimen was initiated in the remaining 84 women (35%). Undetectable viral loads were achieved by 73% of the women by the time of delivery. Relative hazards of time to achieving viral suppression were 1.54 (95% confidence interval, 1.05-2.26) for nevirapine-based HAART versus PI-based regimens and 1.90 (95% confidence interval, 1.16-3.12) for western African versus non-African women. The median duration of time from HAART initiation to achievement of an undetectable viral load was estimated to be 1.4 times greater in women receiving PI-based HAART, compared with women receiving nevirapine-based HAART. Baseline HIV RNA load was also a significant predictor of the rapidity of achieving viral suppression by delivery, but baseline immune status was not. CONCLUSIONS In this study, nevirapine-based HAART (compared with PI [mainly nelfinavir]-based HAART), western African origin, and lower baseline viral load were associated with shorter time to achieving viral suppression.