The menstrual cycle is a natural process that helps in preparing the woman's body for pregnancy. This has four phases: The menstrual phase [day 1 to day 5], follicular phase [day 1 to day 13], ovulation phase [day 14], and luteal phase [day 15 to day 28]. The duration of the menstrual cycle varies from woman to woman.
If the egg released by ovaries during ovulation is not fertilized, the uterus lining sheds through the vagina. And this is called the menstrual period.