Hi, Thanks for posting in HCM. I understand your concern. What your partner is experiencing of early menstrual period after having protected intercourse could be normal. This is because, during the second half of the menstrual cycle (luteal phase), the uterine lining will start to shed down little by little as the hormone progesterone level drops and estrogen becomes dominating. But the cervix would have remained closed while this is happening. When you have intercourse, uterus might contract and cervix can dilate due to orgasms causing menstrual blood to work down faster. The orgasms of cervix will dilate causing vacuum to pull the menstrual blood down and appearance in the form of periods. Such episodes can happen once in a while and when such bleeding occurs, the chances of pregnancy is less likely. Hope the information provided would be helpful. All the best.