The endometrium sheds during menstruation. It then regrows, thickens, is kept for several days through ovulation, and sheds at the next menstruation. The average length of the cycle, from the first day of bleeding of one cycle to the first of another, is 28 days. However, the length and character of the cycle vary greatly among individual women. A period lasts an average of 5 days.
Oral contraceptives contain hormones that prevent the ovaries from releasing an egg.
Without the presence of an egg, conception cannot take place. It is marked by the development of small holes in the bone. It occurs most frequently in women who have gone through menopause. The two ovaries are on each side of the uterus. It occurs about every 4 weeks in the middle of the menstrual cycle, approximately 14 days before the start of the next menstrual period.