McDonald CR, et al. - The authors performed an analysis of longitudinal progesterone and estradiol levels in pregnancy, among human immunodeficiency virus (HIV)–infected pregnant women who were randomized to efavirenz (EFV)-vs lopinavir/ritonavir (LPV/r)-based antiretroviral therapy (ART). In pregnancy, combination ART regimens differentially influenced estradiol levels, which served as a hormone critical to the maintenance of a healthy pregnancy. Identifying Combination antiretroviral therapy (cART) regimens that minimize perinatal HIV transmission without contributing to hormonal dysregulation represented an urgent public health priority.