Menstrual cycle

The menstrual cycle is the female body's monthly pattern of preparing for a possible pregnancy. The uterus grows a new lining called the endometrium; one of the ovaries releases an egg; and then, if the egg is not fertilized by sperm, the endometrium sheds from the uterus as a menstrual period.

• Menstrual phase (period). The thickened lining of the uterus (endometrium) is shed, causing menstrual bleeding. Day 1 of the cycle is the first day of menstrual bleeding. Bleeding usually lasts for 4 to 6 days.
• Follicular phase. The lining of the uterus thickens to prepare for pregnancy. Also, inside a sac (follicle) on the surface of an ovary, an egg (usually one each month) becomes ready to be released.
• Luteal phase. The egg is released (ovulation). Women's ovulation days can range from about day 7 to day 22 of the cycle. But for an individual woman, the ovulation day is usually quite consistent.
  • If the egg is fertilized by sperm, it may attach to (implant in) the lining of the uterus, and pregnancy begins.
  • If the egg is not fertilized or does not implant, the lining of the uterus is shed during the menstrual period, and the cycle starts again.

There is a broad range of "normal" among menstruating women. The average cycle takes 28 days, but 21 to 35 days is considered normal for women in their 20s and 30s. Unpredictable or long menstrual cycles are normal for teenagers and women in their 40s. For teens, normal cycles can be as short as 21 days or as long as 45 days. If you are a teen, you can expect cycles to even out over time. If you are nearing the age of menopause, you can expect menstrual cycles to become longer and eventually to stop.