by Megan Stoddard

Created on: July 24, 2010   Last Updated: September 06, 2010

Every month, as long as a woman is childbearing age and not currently pregnant, her uterus prepares for pregnancy. The whole process usually takes about four weeks, as long as a lunar cycle. However, anywhere from three to five weeks may be within normal range for an individual woman, and sometimes the cycle is less regular than that. Most months, the woman does not get pregnant, so the nest her uterus has prepared for the baby bleeds out. That is called menstruation.

For convenience, since a cycle really has no beginning, let us say that the menstrual cycle begins at the end of a period. Once the uterine lining has bled out, it must build up again. The uterus has a fresh start at preparing itself for pregnancy.

The uterus begins to build up its lining, preparing a space for a developing fetus. After about a week to a week and a half, it is ready. One of the ovaries (every woman has two, one on either side of her body) releases an egg cell. This is called ovulation. The egg travels down the fallopian tube connecting the ovary to the uterus, a journey lasting several days.

If the woman has sex with a man during this time or a few days before, and he releases sperm into her body, the egg may encounter a sperm, either in the uterus or in the fallopian tube, and be fertilized. If it does not, the egg passes out of the body after a few days in the uterus. It passes unnoticed, too small to be seen.

The second half of the cycle now begins. The uterus receives a signal from the body’s hormones that it will soon be time to shed the lining. About two weeks after the egg was released from the ovary (two weeks is the average, but for some women, this time may be as short as ten days or as long as eighteen), the uterus begins to contract slightly. This causes menstrual cramps.

The contractions release the uterine lining, which flows out through the vagina over a period of about a week. For some women, this lasts as little as three days. For others, it lasts as long as eight. The average length is five days. This is called a period, menstrual period, time of the month, or menstruation. More poetically, some women call it moontime.

Though what is coming out looks like blood, and is called menstrual blood, most of it is actually the lining of the uterus. Were the woman pregnant, it would provide a cushion for the baby and a place for the placenta. Since she is not, the lining must be shed before it can build up again for another cycle.

This is what happens in a normal,

• 1
• 2
• Next Page >>