The Menstrual Cycle

The menstrual cycle is the process a woman's body goes through each month as it prepares itself for a possible pregnancy. The cycle ends when a woman gets her monthly period (bleed), and a new cycle begins immediately. Most women begin menstruating in their early to mid-teens and continue until they reach menopause at around age 50. Not all women have neat monthly cycles. For some women, a menstrual cycle lasts 24 days, for others it can last as many as 37 days. Day 1 of the menstrual cycle is considered to be the day on which the menstrual bleed begins.

28 Day Cycle

For the sake of clarity of explanation, we will consider here an "average" cycle of 28 days. Please note that the days on which the various phases of the cycle begin and end, particularly the fertile phase in which a woman can become pregnant, vary from woman to woman. It is not true that the fertile part of the month always and only occurs on day 14 of the cycle.

The Egg Development Phase

The entire menstrual cycle is governed by the levels of female sex hormones present in the body, such as estrogen and progesterone. From days 1 to 14 of the menstrual cycle, increasing estrogen levels encourage an egg to develop to maturity in one of the follicles of one of the ovaries. The medical name for this part of the phase is the "follicular phase."

The Mid-Cycle Phase

Just before day 14, namely right in the middle of the cycle, the brain tells the body to start producing two more sex hormones. One is called FSH (follicle stimulating hormone) and the other is LH (luteinizing hormone). These hormones prepare the ovary for the release of the mature egg. At this point, the estrogen levels in the body are still rising. While all this is going on, the estrogen causes the lining of the uterus to thicken up, getting ready to receive and protect the egg it becomes fertilized.

The Egg Release Phase

The medical name for this phase is the "luteal" phase, and it lasts from day 14 to day 28 of the cycle. During the luteal phase, estrogen levels begin to go down, but progesterone levels start to go up. These high progesterone levels help the uterine lining to maintain its thickness.

On approximately day 14, the egg is finally released by its ovary and makes its way down the fallopian tube to the uterus. At this point, the woman is fertile for a period of 24 to 48 hours. If the egg does not meet a sperm cell on the way and is not fertilized, progesterone levels begin to drop and continue to decrease until day 28. When the progesterone levels reach their lowest point, on the day before bleeding begins, the uterine lining breaks up.

On the first day of menstruation, which is actually day 1 of the next cycle, the uterine lining and the egg are flushed out of the woman's body as blood, via the vagina. This is the monthly period.

The Bleeding Phase

The bleeding phase of the cycle, or "menstruation," usually lasts between 3 and 7 days. Most women lose between 3 and 5 tablespoons of blood. Menstruation may be accompanied by certain symptoms such as pain, bloating and cramping.