Menstruation is the dropping of the uterine lining (endometrium), which is followed by bleeding. But during pregnancy, it happens in roughly monthly cycles throughout a woman’s reproductive life. Menstruation begins with puberty (at menarche) and ends with menopause.
The menstrual cycle officially begins on the first day of bleeding, which is referred to as day 1. The cycle comes to an end immediately before the start of the following menstrual period. Menstrual periods usually last between 25 and 36 days. Only about ten to fifteen percent of women have 28-day periods. In addition, at least 20% of women have irregular cycles. That is, they are outside of the regular range in length or width. In the years immediately after menstruation begins (menarche) and before menopause, the cycles vary the most and the intervals between periods are the longest.
Menstrual bleeding can last anywhere from 3 to 7 days, with an average of 5 days. During a cycle, blood loss normally varies from 1/2 to 2 1/2 ounces. Depending on the variety, a sanitary pad or tampon can hold up to an ounce of blood. Unlike blood after an injury, menstrual blood normally does not clot unless the bleeding is quite heavy.
Hormones play a role in the menstrual cycle. The pituitary gland creates luteinizing hormone and follicle-stimulating hormone, which encourage ovulation and stimulate the ovaries to produce estrogen and progesterone. Estrogen and progesterone provide the uterus and breasts for prospective conception by stimulating them.
The menstrual cycle is divided into three stages
On the first day of menstrual bleeding, the follicular phase begins (day 1). The growth of follicles in the ovaries, however, is the most important occurrence in this phase.
The uterine lining (endometrium) is thick with fluids and nutrients designed to nourish an embryo during the start of the follicular phase. Estrogen and progesterone levels are inadequate if no egg has been fertilized. Menstrual bleeding happens as a result of the top layers of the endometrium being lost.
The pituitary gland marginally boosts its synthesis of the follicle-stimulating hormone at this period. The growth of 3 to 30 follicles is then stimulated by this hormone. Each follicle is home to an egg. As the level of this hormone drops later in the phase, only one of these follicles (known as the dominant follicle) continues to grow. It starts producing estrogen right away, and the other exciting follicles start to break down. Increased estrogen also starts to prepare the uterus and encourages the release of luteinizing hormone.
The follicular phase lasts about 13 or 14 days on average. This phase is the one that varies the greatest in length among the three. It tends to get shorter as you get closer to menopause. When the level of luteinizing hormone rises considerably, this period comes to a conclusion (surges). The surge causes the egg to be released (ovulation), signaling the start of the following phase.
When the amount of luteinizing hormone rises, the ovulatory phase begins. The dominant follicle is stimulated to expand from the ovary’s surface and eventually burst, releasing the egg. Follicle-stimulating hormone levels rise, but only a little. The rise in follicle-stimulating hormone has an unknown purpose.
The ovulatory period lasts 16 to 32 hours on average. It comes to an end when the egg is discharged, typically 10 to 12 hours after the luteinizing hormone level rises. Only around 12 hours after the egg is released can it be fertilized.
Luteinizing hormone levels in the urine can be used to detect a rise in the hormone. This metric can be used to figure out when a woman is fertile. When sperm are present in the reproductive tube before the egg is released, fertilization is more likely. When intercourse happens within three days of ovulation, the majority of pregnancies occur.
Some women have dull pain on one side of their lower abdomen around the time of ovulation. The pain is referred to as mittelschmerz (literally, middle pain). The embarrassment can last anywhere from a few minutes to several hours. The pain normally occurs on the same side as the ovary that delivered the egg, but the exact cause is uncertain.
After ovulation, the luteal phase begins. It lasts approximately 14 days (unless fertilization happens) and stops right before menstruation.
After releasing the egg, the ruptured follicle closes and develops a tissue called the corpus luteum, which generates increasing amounts of progesterone. The corpus luteum’s progesterone has the following effects:
- Readies the uterus for the possible implantation of an embryo.
- Causes the endometrium to thicken, allowing fluids and nutrients to enter and nourish a developing embryo.
- Causes the mucus in the cervix to thicken, making it less likely for sperm or germs to enter the uterus.
- During the luteal phase, the body temperature rises slightly and stays there until the menstrual period begins (this increase in temperature can be used to estimate whether ovulation has occurred)
The estrogen level is high for the majority of the luteal period. Estrogen causes the endometrium to thicken as well.
The widening of milk ducts in the breasts is caused by an increase in estrogen and progesterone levels (dilate). The breasts may enlarge and become painful as a result.
The corpus luteum degenerates after 14 days if the egg is not fertilized or if the fertilized egg does not implant, estrogen and progesterone levels drop, and a new menstrual cycle begins.
The cells around the growing embryo begin to generate a hormone called human chorionic gonadotropin once the embryo is implanted. Until the growing fetus can manufacture its own hormones, this hormone keeps the corpus luteum functioning and producing progesterone. The detection of an increase in human chorionic gonadotropin level is the basis for pregnancy testing.