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 shedding of the uterine lining (endometrium), accompanied by bleeding. It begins at puberty and ends at menopause, occurring monthly except during pregnancy.

The menstrual period starts on the first day of the cycle, and a menstrual cycle is 28 days long, 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 for 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 produce estrogen and progesterone. These two hormones stimulate the uterus and the senses in preparation for potential fertilization.

The start of the cycle and the follicular phase

The first day of your period is considered the first day of your cycle. During this phase, known as the follicular phase, several key processes occur. First, hormone levels, especially estrogen, begin to rise, which stimulates the development of follicles in the ovaries. Each of these follicles contains an immature egg. As the cycle progresses, one dominant follicle emerges, while the others shrink.

• The pre-ovulatory phase, also called the follicular phase

At the beginning of this phase, estrogen and progesterone levels are low. The superficial layers of the uterine lining break down and are shed, which is when bleeding starts. So, bleeding marks the beginning of the follicular phase, but the main event of this phase is the development of follicles in the ovaries.

FSH (follicle-stimulating hormone) levels slightly increase, leading to the development of many follicles, each containing an egg.

Later, as FSH levels decrease, only one follicle continues to develop and produces estrogen.

The follicular phase lasts between 13 and 14 days.

• The ovulatory phase (when the follicle releases the egg)

Around the middle of the cycle, typically around day 14 in a 28-day cycle, a surge in LH (luteinizing hormone) triggers the release of the mature egg from the follicle into the fallopian tube, where it is available for fertilization by sperm. This phase usually lasts approximately 24 hours: between 16 and 32 hours.

Estrogen levels decrease during this surge, and progesterone levels then begin to rise.

• 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 up and transforms into the corpus luteum, which secretes progesterone. This hormone is essential for preparing the uterus for a possible implantation by thickening the uterine lining.

This corpus luteum also thickens the cervical mucus, reducing the likelihood of sperm and bacteria entering the uterus, and causes a slight increase in basal body temperature that remains elevated until your period begins.

If the egg is not fertilized, the corpus luteum shrinks, stops producing progesterone, and estrogen levels decrease. The uterine lining breaks down and is shed, leading to menstrual bleeding, which marks the beginning of a new cycle.

If an embryo implants, the cells surrounding it produce a hormone called human chorionic gonadotropin. This hormone maintains the corpus luteum and its production of progesterone, until the fetus is able to produce its own hormones. Pregnancy tests work by detecting the increase in human chorionic gonadotropin levels.

Variations and Factors Influencing the Menstrual Cycle

While the menstrual cycle is generally 28 days long, it's important to note that it can vary significantly from one woman to another. Shorter or longer cycles are common and can be influenced by various factors, including stress, hormonal changes, illnesses, weight fluctuations, and medications. Irregular menstrual cycles can sometimes indicate an underlying issue that requires medical evaluation.

Indicators of Reproductive Health

Some women use biological indicators to track their menstrual cycle and fertility. These indicators include basal body temperature, which slightly increases after ovulation, and cervical mucus, which becomes clearer and more stretchy during the fertile window. These signs can help women identify their fertile days to optimize their chances of conception or, conversely, to avoid an unwanted pregnancy.

Why Do Periods Hurt?

Dysmenorrhea is the medical term for abdominal and pelvic pain that occurs before or during menstruation.

This pain usually lasts one to three days, starting with bleeding and being most intense when bleeding is heaviest. It can sometimes be felt a little before menstruation and occasionally continue a short while after. Dysmenorrhea is typically felt in the lower abdomen (pelvis), but can spread to the back and thighs.

Dysmenorrhea is very common and, most often, not serious.

This phenomenon is caused by an excessive secretion of prostaglandins by the uterine lining during menstruation. These substances cause uterine contractions to help shed the uterine lining. An excess of prostaglandins leads to an abnormal increase in the contractility and tone of the uterine muscle. These abnormally frequent contractions deprive the uterine muscle of oxygen (hypoxia) by compressing small blood vessels, and this hypoxia causes the pain.

If dysmenorrhea worsens and the pain becomes increasingly severe over time, an underlying cause is investigated, such as a malformation of the vagina or uterus, endometriosis, uterine fibroids, or adenomyosis.

In conclusion, the menstrual cycle is a complex and essential process in female sexual life, regulating fertility and reproductive health. While 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 about 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.