Abstract Among 396 HIV-infected women conceiving on combination antiretroviral therapy and enrolled in the European Collaborative Study in 2000-2011, the proportion with virological failure (>200 copies/ml after ≥24 weeks of treatment) declined substantially from 34% in 2000-2001 to 3% in 2010-2011. In adjusted analyses, younger women and those with at least two children were at increased risk of virological failure, highlighting the importance of close monitoring and adherence support