All about the menstrual cycle | duration, phases and variations

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 uterine lining (endometrium), accompanied by bleeding. They begin at puberty and end at menopause, and occur every month except during pregnancy.

Menstruation begins on the first day of the cycle, and a menstrual cycle is 28 days long, although individual variations are common. In fact, only 10-15% of women have a 28-day cycle.

Bleeding normally 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 synchronized 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 to create estrogen and progesterone. These two hormones stimulate the uterus and the senses for eventual 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 take place. First, hormone levels, particularly estrogen, begin to rise, stimulating 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 known as the 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 thus marks the start of the follicular phase, but the main event that marks this phase is the development of follicles in the ovaries.

FSH (follicle-stimulating hormone) levels rise slightly, inducing the development of numerous follicles, each containing an egg.

Later, when FSH levels fall, a single follicle continues to develop and produce estrogen.

The follicular phase lasts between 13 and 14 days.

• The ovulatory phase (the follicle releases the egg)

Towards the middle of the cycle, generally around day 14 in a 28-day cycle, a peak in luteinizing hormone (lh) triggers the release of the mature ovum from the follicle into the fallopian tube, where it is available for fertilization by a spermatozoon. into the fallopian tube, where it is available for fertilization by a spermatozoon. This phase generally lasts approximately 24 hours: between 16 and 32 hours.

Estrogen levels fall at this peak, and progesterone levels begin to rise.

• The luteal phase

 This phase lasts around 14 days, regardless of the total length of the cycle.

LH and FSH levels fall, and the empty follicle closes and transforms into a corpus luteum, which secretes progesterone, an essential hormone to prepare the uterus for implantation by thickening the uterine lining.

This corpus luteum will also thicken cervical mucus, reducing the likelihood of sperm and bacteria entering the uterus, and causing a slight rise in basal body temperature that is maintained until the onset of menstruation.

If theegg is not fertilized, the corpus luteum regresses, no longer producing progesterone, and estrogen levels fall. The uterine lining degenerates and is shed, and menstrual bleeding occurs, marking the start of a new cycle.

When an embryo is implanted, the cells around the embryo produce a hormone called human chorionic gonadotropin. This hormone maintains the corpus luteum and its production of progesteroneAs long as the fetus is unable to produce its own hormones, the pregnancy test will be carried out. Pregnancy tests are based on the detection of increased levels of human chorionic gonadotropin.

Variations and factors influencing the menstrual cycle

Although the menstrual cycle is generally 28 days long, it's important to note that it can vary considerably from one woman to another. Shorter or longer cycles are common and can be influenced by a variety of factors, including stress, hormonal changes, illness, weight fluctuations and medication. Irregular menstrual cycles can sometimes be a sign of an underlying problem requiring medical evaluation.

Reproductive health indicators

Some women use biological indicators to monitor their menstrual cycle and fertility. These indicators include basal body temperature, which rises slightly after ovulation, and cervical mucus, which becomes lighter 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 an unwanted pregnancy.

Why do periods hurt?

Dysmenorrhea is the medical term given to abdominopelvic pain that precedes or accompanies menstruation.

These pains usually last one or three days, starting with bleeding and peaking when the bleeding is heaviest. They may be felt a little before the period and sometimes last a little longer afterwards. Dysmenorrhea is usually felt in the lower abdomen (pelvis), but can extend to the back and thighs.

The dysmenorrhea is very common and, more often than not, not serious.

This is a phenomenon linked to excess secretion of prostaglandins by the uterine mucosa at the time of menstruation. These substances trigger uterine contractions to facilitate expulsion of the uterine mucosa. An excess of prostaglandins causes an abnormal increase in the contractility and tone of the uterine muscle. These abnormally frequent contractions deprive the uterine muscle of oxygen (hypoxia) through compression of the small vessels, and this hypoxia causes pain.

If dysmenorrhea worsens and the pain gets worse over time, an underlying cause is sought, such as a malformation of the vagina or uterus, endometriosis, uterine fibroids, 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 lasts 28 days, it can vary from one woman to another and be influenced by a variety of factors. Understanding the different phases of the menstrual cycle and being aware of the signs of reproductive health can help women take care of their overall well-being and make informed decisions about their fertility.

 

Sources

1. The menstrual cycle. Jessica E. McLaughlin, MD, Medical University of South Carolina

2. Pain during menstruation. Ameli Assurance Santé.