Yeganeh N, et al. - Researchers here evaluate the prevalence and the effect of HIV antiretroviral drug resistant mutations (DRMs) in previously untreated mother-infant pairs. They identify a common occurrence of pre-existing DRMs in untreated HIV infected pregnant women but these do not increase the risk of HIV mother to child transmission. However, if women with DRMs are not virologically suppressed, they can transmit resistant mutations and complicate infant management.