Sexual intercourse at the time of embryo implantation may lower the chance of becoming pregnant according to a study published in Fertility and Sterility (Fertil Steril 2014;102:178-82). A large prospective study from the University of North Carolina included a total of 564 women undergoing 1,332 complete cycles found that having intercourse from 5 days after ovulation to 9 days after ovulation corresponding to 3 to 9 days before the end of the menstrual cycle significantly lowered the probability of becoming pregnant. Couples who had intercourse on 2 or more days during the peri-implantation window were 40% less likely to become pregnant compared with couples who did not have intercourse during the peri-implantation window. The probability of pregnancy further decreased with the number of days with intercourse during the peri-implantation window. Sexual intercourse at the time of implantation could theoretically induce a pro-inflammatory response that may interfere with embryo implantation.