In some women it's slightly longer, in others it's slightly shorter. But the entire point of this menstrual cycle is to ultimately prepare that woman for a possible pregnancy. And more specifically, it's to prepare the lining of the uterus for a possible implantation by a zygote. Now we know a zygote is only formed if the woman is sexually active, if fertilization actually takes place. But most of the time fertilization does not take place. So what happens during the menstrual cycle?