My husband and I had sex during my menstrual cycle. Right after the sex, my period just stopped, and I wasn't bleeding anymore. Why does this happen?

J.

When it is time for your period to begin, the endometrium (uterine lining) produces chemicals called prostaglandins. These hormone-like substances occur throughout the body and play many roles. In the uterus, their release provokes muscular contractions that constrict uterine blood vessels. This causes the uterus to shed the endometrium, starting the menstrual period. Prostaglandins are also responsible for the uterine muscle contractions that some women feel as menstrual cramps.

When a man ejaculates, his body also produces prostaglandins, which are released in the semen. Seminal plasma prostaglandins, entering the woman, can intensify the uterine contractions already occurring with her period. This effect can be heightened by the contractions of orgasm. These intense uterine contractions can hasten the expulsion of the dying uterine lining cells. In some cases, if the remainder of the endometrium is shed at once, this can complete the woman's period.