Hormones and the Menstrual Cycle

Menstrual cycle hormones control the shedding of the lining of the uterus that is indicated by bleeding. Menstruation is necessary for reproduction and is considered the marker of the reproductive years of women. The start of menstruation is called menses and the end is called menopause.

Many times women have questions about what is normal and what isn’t in their cycles. Sometimes, when trying to get pregnant women aren’t sure what is happening with their bodies. Women should have a basic knowledge of what is happening in their bodies to help their physician diagnose any problems if they come up.

Menstrual cycles are actually counted from the start of bleeding of one cycle to the 1st day of bleeding of the next – NOT from the end of one cycle to the beginning of the next as many women believe.

Cycles are usually between 25 and 35 days and only 10% of women have the ‘standard’ 28 day cycle. Menstrual cycle hormones control the phases of preparation for pregnancy; two are produced by the pituitary gland and two by the ovaries.

The pituitary gland controls the production and release of luteinizing hormone and follicle stimulating hormone. The ovaries produce estrogen and progesterone.

During the first 13 days of the cycle the uterus starts to build up the lining in preparation for a potential pregnancy. This is the follicular phase that lasts until a surge of luteinizing hormone that spurs the release of an egg for ovulation. The follicular phase gets shorter during menopause.

Menstrual cycle hormones in the follicular phase, produced by the pituitary gland, are follicle-stimulating hormone that stimulates the ovaries to produce 1-20 eggs. As the level of the hormone decreases only one egg continues to grow; this is the dominant egg.

The dominant egg is expelled from the ovaries and leaves behind an empty shell called the corpus luteum.

The next phase is the ovulatory phase and is characterized by the release of the egg. After the egg is released the corprus luteum secretes estrogen and progesterone to support the lining of the uterus. If no egg is fertilized then the hormone levels fall off and causes the body to shed the lining of the uterus – menstruation.

Blood loss during menstruation averages 4 ½ ounces per month with a low end of ½ ounce and a high loss of 10 ounces. Most women feel that these amounts are not accurate but unless there is heavy bleeding caused from an abnormal medical diagnosis the amount of loss has been measured through several studies.

Menstrual cycle hormones complete the three phases with the luteal phase, following the ovulatory phase, which lasts about 14 days.

These phases appear to overlap between the luteal phase and the follicular phase. However, it is difficult to predict the start of one phase to the other without hormone levels being drawn.

This happens to all women and all women have a responsibility to have a basic understanding of what happens.