Many women do not give the menstrual cycle much thought. They take note when their periods start and forget about it the rest of the month. When a problem becomes noticeable, such as infertility or heavy bleeding, they begin to realize the importance of recording the start of their periods and taking note of what happens the rest of the month. The menstrual cycle is a complex system of hormonal fluctuations. Changes in the menstrual cycle can be an indicator of pregnancy, or that something is wrong. Understanding the menstrual cycle can also be helpful when trying to get pregnant.
Normal Menstrual Cycle
The menstrual cycle begins with menstruation, which lasts three to seven days. The second week is marked by the development of a dominant ovarian follicle triggered by the release of follicle-stimulating hormone (FSH) from the pituitary gland. The follicle releases estradiol, a form of estrogen, which is responsible for thickening the uterine lining. The follicle must adequately grow to produce a fertile egg.
Ovulation is marked by the rupturing of the follicle to release the egg. The egg is swept into the fallopian tube where it may be fertilized by sperm. When the follicle ruptures, it becomes a corpus luteum cyst that excretes progesterone. The progesterone prepares the inner lining of the uterus for egg implantation should fertilization occur. If fertilization does not occur, estrogen and progesterone levels drop and menstruation begins.
The following is a summation of the menstrual cycle:
- Menstruation – the monthly "period"
- Proliferative phase – the pituitary gland releases FSH stimulating the growth of a follicle
- Ovulation – the mature follicle ruptures and releases an egg, or ovum
- Luteal phase (also known as the secretory phase) – the ruptured follicle, which is called the corpus luteum, releases progesterone to prepare the endometrium, the inner lining of the uterus, for implantation of the fertilized egg
Abnormal Menstrual Cycle
Several conditions may cause an imbalance with the hormones that regulate the menstrual cycle. Infertility may result from premature ovulation – the release of the egg before the dominant follicle is mature. Ovulation may not occur in some women. Long heavy periods or bleeding in between periods may result. Some women may experience amenorrhea, which is the absence of menstruation.
Keeping track of the menstrual cycle by at least taking note of the first day of each menstrual period is important. The first day of the menstrual period is referred to as the LMP (last menstrual period) and is used to diagnose any irregularities in the menstrual cycle. These irregularities can be caused by fibroids, polycystic ovarian syndrome, and other gynecological problems. The LMP is also used to determine gestational age should pregnancy occur.
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