Introduction
PROSTATE
The Evidence for Contraceptive Options and HIV Outcomes (ECHO) trial, which randomized women to three different contraceptive methods including intramuscular injectable depot medroxyprogesterone acetate (DMPA-IM), a copper intrauterine device (Cu-IUD) and a levonorgestrel (LNG) implant, found no significant differences in HIV acquisition between the contraceptive methods. Due to the nature of the contraceptive methods under study, neither study participants nor research staff at the study sites were blinded. We aimed to evaluate whether there were any post-randomization differences in condomless vaginal sex (hereafter sexual behavior), and thus potentially to HIV exposure, by randomized contraceptive group using prostate specific antigen (PSA) as an objective marker of recent condomless vaginal sex. PSA has been used in multiple studies as a valid proxy measure for recent condomless vaginal sex and is detectable in vaginal fluid immediately following condomless vaginal sex, and generally returns to undetectable levels within 48 h [