BackgroundMother to child transmission (MTCT) of HIV remains a challenge in resource-limited settings. Central to elimination of MTCT is effective Provider Initiated HIV Counseling and Testing (PICT). Research has shown that conducting PICT only at the initial antenatal care (ANC) visit fails to benefit pregnant women who seroconvert later in their pregnancy. This study aimed to determine the most cost effective time to perform repeat HIV testing during ANC and perinatal care (PNC). MethodsWe studied the repeat HIV testing results of pregnant women � 18 and adolescent girls aged 15-17 in the Sauri, Kenya Millennium Villages Project (MVP) site. Nurses provided HIV screening to 1,403 expectant women and 256 adolescent girls following the 1 st , 2 nd , 3 rd and 4 th ANC visits, at birth and 6 and 14 weeks postpartum. ResultsFive women seroconverted during the study period (incidence proportion 0.41%). One woman seroconverted at the 2 nd ANC visit, another one at the 3 rd , two at the 4 th and one at 6 weeks post-partum. Of all the women who seroconverted, four reported an HIV negative primary partner, while one reported an unknown partner status. None of the participants reported condom use during pregnancy. Two of the seroconverters vertically transmitted HIV to their babies. The results did not suggest a clear pattern of seroconversion during ANC and PNC.