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
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 becomes ready to be
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
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
Sarah Marshall, MD - Family Medicine & Femi Olatunbosun, MB, FRCSC - Obstetrics and Gynecology