Infectious Diseases in Obstetrics and Gynecology PSA, a glycoprotein produced by the prostate gland and secreted into the seminal plasma, was ﬁrst identiﬁed by forensic scientists who were trying to ﬁnd a substance in seminal ﬂuid to facilitate the investigation of rape cases [29]. More recently, PSA has been used in contraception and HIV/STI research to assess recent (i.e., within the previous 48 hours) exposure to semen [30–33]. While several laboratory assays can be employed to quantify PSA levels or other biomarkers of semen exposure (e.g., Y-chromosome DNA), they require specialized laboratory equipment and training. More recently, a low-cost, rapid test that can be used by laboratory technicians without specialized training has been showed to provide reliable and valid semiquantitative measures of PSA and, thus, makes the use of PSA as a semen biomarker feasible in a wide range of research settings [34]. 3. Challenges to Study Design Ideally, such a study would be conducted in a site in which the women normally do not have access or are na¨ıve to use of the speciﬁc LARC method. Participants would be randomized to receive the LARC method at enrollment or after the end of followup. Precedent for this type of design in which the introduction of the intervention is delayed in the control arm until the end of study participation can be found, for example, in the recent trials on the eﬀect of circumcision on HIV acquisition in which men were randomized to immediate or delayed circumcision [35]. Ethically, investigators cannot withhold a LARC method (even for a limited interval) from women in settings where the normal standard of care allowed for its provision. Consequently, depending on the availability of the LARC method, this study design might not be feasible in all settings. Another limitation is the potential for the request for swab collection to inﬂuence participant behavior. Women could either be asked for their consent to test their col- lected vaginal specimens for PSA at time of enrollment or, retroactively, at their last study visit. Although a randomized controlled trial did not ﬁnd evidence that the advance knowledge of testing for PSA caused women to report more unprotected sex [36], such knowledge still could cause women to modify their behavior (e.g., abstain from unprotected sex before study visits). Asking for consent for PSA testing retroactively circumvents the possibility of behavioral change from swab collection; however this approach requires another reason to justify swab collection during the study (e.g., as an opportunity for STI testing) and would risk losing data from women who do not return for their last visit or who decline to consent to the testing. Regardless of the timing of the consenting process for PSA testing, women simply might tend to change behavior in general before attending study visits; for example, women may abstain from sex before a scheduled pelvic examination due to hygienic concerns. Any study of risk compensation will have problems with generalizability. Even if the proposed study does not demon- strate evidence of condom migration from the initiation of the contraceptive implant, this would not preclude its 3 occurrence in other settings or with other populations. The eﬀect of adopting a LARC method on participant levels of condom use could vary by numerous factors, including participant characteristics, participant perceived risk of STIs, quality of provider counseling and patient-provider rapport, and social norms surrounding condom use. Study ﬁndings from one setting cannot be assumed to be generalizable to other populations. 4. Conclusions The proposed study design addresses two methodical weaknesses (i.e., reliance on self-reported data and lack of randomized design) that have limited the interpretation of ﬁndings from previous studies on this topic. More broadly, the detection of semen biomarkers could be applied to research on condom migration associated with other contraceptive methods and with HIV-prevention interventions, including male circumcision and oral or topical microbicides. Given that the occurrence of condom migration from the introduction of LARC methods or HIV- prevention interventions could vary by study populations, the utility of testing for PSA might be even more useful for on-going, population-level surveillance of changes in condom use patterns. This surveillance could provide accurate information with which to identify subgroups in a setting that might beneﬁt from more intensive condom counseling. Also, by monitoring the frequency of PSA detection in a population, providers could evaluate and compare the eﬀectiveness of diﬀerent methods of counseling on condom use. Researchers should consider incorporating testing for semen biomarkers routinely into studies as well as surveillance requiring measures of unprotected sex. Acknowledgment The ﬁndings and conclusions in this report are those of the authors and do not necessarily represent the oﬃcial position of the Centers for Disease Control and Prevention or FHI 360. References [1] American College of Obstetricians and Gynecologists Com- mittee on Gynecologic Practice; Long-Acting Reversible Con- traception Working Group, “ACOG Committee Opinion no. 450: increasing use of contraceptive implants and intrauterine devices to reduce unintended pregnancy,” Obstetrics and Gynecology, vol. 114, no. 6, pp. 1434–1438, 2009. [2] A. Glasier, “Should healthcare professionals be advocating long-acting reversible contraception?” Women’s Health, vol. 5, no. 1, pp. 1–4, 2009. [3] W. Cates and M. J. Steiner, “Dual protection against unin- tended pregnancy and sexually transmitted infections: what is the best contraceptive approach?” Sexually Transmitted Diseases, vol. 29, no. 3, pp. 168–174, 2002. [4] National Institute of Allergy and Infectious Diseases, Work- shop Summary: Scientiﬁc Evidence on Condom Eﬀectiveness for