BACKGROUND: The burden of HIV infection constitutes a major public health concern worldwide. Nigerian HIV/AIDS disease burden is the third largest worldwide. In addition, acute HIV infection (sero-conversion) in pregnancy is of paramount importance because of its associated higher risk of vertical transmission. OBJECTIVE: This study was aimed at detecting booked patients, who at registration were in the window period of immunodeficiency virus infection, but tested reactive to a repeat HIV screening in labour and also to determine the proportion of patients that would otherwise have been missed. MATERIALS AND METHODS: All booked patients were offered counselling and testing with opt-out option at booking. The patients found to be non-reactive had the screening repeated in labour by parallel testing with two different rapid test kits, if three months or more had elapsed after the initial screening.