The menstrual cycle, a complex and crucial phenomenon in female reproductive health, is the result of a harmonious orchestration between various hormones and biological processes. Menstruation is characterized by the loss of the lining of the uterus (endometrium), accompanied by bleeding. They begin at puberty and end at menopause and occur every month except during pregnancy.
The period begins on the first day of the cycle and a menstrual cycle is 28 days , although individual variations are common. In fact, only 10 to 15% of women have a 28-day cycle.
Normally, bleeding lasts between 4 and 8 days of the cycle and blood loss varies from 6 to 70mL.
This process, essential to human reproduction, involves a series of carefully timed events that prepare the body for fertilization and is regulated by hormones. Luteinizing and follicle-stimulating hormones, produced by the pituitary gland, promote ovulation and stimulate the ovaries which will create estrogen and progesterone. These two hormones stimulate the uterus and the senses in preparation for possible fertilization.
The beginning of the cycle and the follicular phase
The first day of menstruation is considered the first day of the cycle. During this phase, known as the follicular phase, several key processes occur. First, hormone levels, particularly estrogen, begin to increase, which stimulates the development of follicles in the ovaries . These follicles each contain an immature egg. As the cycle progresses, a dominant follicle emerges, while the others regress.
- The pre-ovulatory phase also called follicular phase
At the start of this phase, estrogen and progesterone levels are low. The superficial layers of the uterine mucosa disintegrate and are evacuated: bleeding begins. Bleeding therefore marks the beginning of the follicular phase but the main event which marks this phase is the development of follicles in the ovaries.
The level of FSH (follicle-stimulating hormone) increases slightly, inducing the development of numerous follicles, each composed of one egg.
Later, when FSH levels decrease, a single follicle continues to grow and produces estrogen.
The follicular phase lasts between 13 and 14 days.
- The ovulatory phase (the follicle releases the egg)
Toward the middle of the cycle, usually around day 14 in a 28-day cycle, a spike in luteinizing hormone triggers the release of the mature egg from the follicle into the fallopian tube , where it is available for fertilization by a sperm. This phase generally lasts approximately 24 hours: between 16 and 32 hours.
Estrogen levels decrease during this peak and the increase in progesterone levels then begins.
- The luteal phase
This phase lasts approximately 14 days, regardless of the total cycle length.
LH and FSH levels decrease and the empty follicle closes and transforms into the corpus luteum, which secretes progesterone, a hormone essential to prepare the uterus for possible implantation through the thickening of the uterine lining.
This corpus luteum will also thicken the cervical mucus , thus reducing the probability of sperm and bacteria entering the uterus and causing a slight rise in basal body temperature which is maintained until the onset of menstruation.
During most of the luteal phase, estrogen levels is high and elevation in estrogen levels and of progesterone causes dilation of the milk ducts of the breasts. The breasts, as a result, may swell and become painful.
If the egg is not fertilized , the corpus luteum regresses, no longer produces progesterone and estrogen levels decrease. The uterine lining degenerates and sheds, menstrual bleeding occurs, marking the start of a new cycle.
When an embryo is implanted, cells placed around the embryo produce a hormone called human chorionic gonadotropin. This hormone maintains the corpus luteum and its production of progesterone , as long as the fetus is not able to produce its own hormones. Pregnancy tests rely on detecting increased levels of human chorionic gonadotropin.
Variations and factors influencing the menstrual cycle
Although the menstrual cycle is generally 28 days, it is important to note that it can vary greatly from woman to woman. Shorter or longer cycles are common and can be influenced by a variety of factors, including stress, hormonal changes, illness, weight fluctuations, and medications. Irregular menstrual cycles can sometimes be a sign of an underlying problem that requires medical evaluation.
Reproductive health indicators
Some women use biological indicators to track their menstrual cycle and fertility. These indicators include basal body temperature , which increases slightly after ovulation, and cervical mucus, which becomes clearer and more stretchy during the fertile period. These signs can help women identify their fertile days and optimize their chances of conception or, conversely, avoid unwanted pregnancy.
Why do periods hurt?
Dysmenorrhea is the medical term given to abdominopelvic pain that precedes or accompanies menstruation.
This pain generally lasts one or three days and begins with the bleeding and is greatest when the bleeding is heaviest. They can already be felt a little before your period and sometimes continue a little after it. Dysmenorrhea is usually felt in the lower abdomen (pelvis), but can extend to the back and thighs.
There Dysmenorrhea is very common and, most often, not serious.
This is a phenomenon linked to excess secretion of prostaglandins by the uterine mucosa during menstruation. These substances cause uterine contractions to facilitate the expulsion of the uterine lining. An excess of prostaglandins causes an abnormal increase in contractility and tone of the uterine muscle. These abnormally frequent contractions deprive the uterine muscle of oxygen (hypoxia) by compression of the small vessels and this hypoxia causes pain.
If dysmenorrhea worsens and the pain becomes more severe over time, an underlying cause is sought such as a malformation of the vagina or uterus, endometriosis, uterine fibroid, adenomyosis ...
In conclusion, the menstrual cycle is a complex and essential process in female sexual life, regulating fertility and reproductive health. Although the average menstrual cycle is 28 days, it can vary from woman to woman and be influenced by various factors. Understanding the different phases of the menstrual cycle and being aware of reproductive health signs can help women take care of their overall well-being and make informed decisions regarding their fertility.
Sources
1. The menstrual cycle. Jessica E. McLaughlin, MD, Medical University of South Carolina
2. The occurrence of pain during menstruation. Ameli Health Insurance.