Decreased sexual motivation during the human implantation window

Abstract

The implantation window denotes cycle days when the endometrium is receptive to an implanting blastocyst. Research supports increased risk of some types of sexually transmitted infections at this time due to local immunosuppression that facilitates the implantation process. This heightened infection risk may have selected for downregulation of sexual motivation within the mid-luteal phase days that comprise the human window of implantation. Here, using data from three large, daily diary studies (N > 2500 observations) among undergraduate participants, we tested whether measures of women's sexual motivation were dampened during the implantation window. Multi-level regression analyses on the combined sample demonstrated significant drops in multiple measures of sexual motivation within the estimated implantation window relative to other cycle regions. Furthermore, for most measures, sexual motivation was significantly lower during the implantation window relative to non-menstrual cycle days outside the fertile window, such that mid-luteal drops in desire and behavior were not statistical artifacts of elevations in sexual motivation during the fertile window. These findings are consistent with evolved, functional responses to temporal fluctuations in infection risk that may help to explain cycle phase shifts in human sexual motivation.