Menstrual Cycle Phases And Their Impact On Female Fertility

The menstrual cycle refers to the sequence of events that occur in the body of a woman of reproductive age, from the first day of menstruation to the day before the next menstruation. Although the average duration is 28 days, this can vary between 21 and 35 days, and each woman may experience slight variations. Importantly, during puberty and menopause, hormones can fluctuate, which can lead to irregular cycles.

The menstrual cycle is controlled by a delicate balance of hormones produced in different glands of the body, such as the hypothalamus, pituitary gland and ovaries. These hormones act together to carry out different stages that prepare the body for possible conception and pregnancy.

Menstrual cycle phases

Menstrual phase: Goodbye to the endometrium

The cycle begins with the menstrual phase, also known as menstruation or period. During this phase, estrogen and progesterone levels, which had increased during the previous cycle, drop considerably. The decrease in these hormones causes the blood vessels that nourish the endometrium to contract, leading to the disintegration of the superficial layer of the uterine lining.

This process is essential to remove the endometrial cells that were prepared to receive and nourish a fertilized egg in the previous cycle. The mixture of blood, endometrial cells and cervical mucus forms what we know as menstruation, which is expelled through the vagina for about 3 to 7 days, on average.

Follicular phase: The follicles take center stage!

Once menstruation has ended, the body enters the follicular phase. During this stage, the pituitary gland secretes follicle-stimulating hormone (FSH), which stimulates the ovarian follicles to mature. Each follicle contains an immature egg, and as they grow, they begin to produce estrogen.

Estrogen plays a crucial role in this phase by preparing the uterus for a possible pregnancy. This involves thickening the endometrium and creating a favorable environment for implantation of the fertilized egg. In addition, estrogen also stimulates cervical mucus to facilitate the passage of sperm into the egg.

Ovulation: The most fertile time of the cycle

The ovulation phase is a crucial and exciting time of the menstrual cycle. On day 14 of the cycle (on average), an increase in luteinizing hormone (LH) causes the larger and more mature follicle to rupture, releasing the egg into the fallopian tube. The egg is ready to be fertilized for the next 12 to 24 hours.

If fertilization occurs during this short period of time, the fertilized egg will travel to the uterus and implant in the endometrium, beginning pregnancy. However, if the egg is not fertilized, the next phase of the menstrual cycle begins.

Luteal Phase: Preparing for Pregnancy

Once the egg is released, the follicle that contained it is transformed into a structure called the corpus luteum. This small gland begins to produce progesterone, which is crucial for keeping the uterine lining thick and ready to receive a fertilized egg.

Progesterone also contributes to raising the basal body temperature and modifying the cervical mucus to make it less conducive to the passage of sperm. All this is done in order to create an unfavorable environment for a second egg, thus avoiding the possibility of a multiple pregnancy.

Why menstruation: Why doesn’t pregnancy always occur?

Menstruation occurs when the egg released during ovulation is not fertilized and pregnancy does not occur. In the absence of a developing embryo requiring nutrition, the body does not need the thickened uterine lining and therefore discards it through menstruation.

This process ensures that the uterus is clean and ready to receive a new fertilized egg in the next menstrual cycle. Importantly, although menstruation can be thought of as “lost blood,” it is actually a combination of blood, endometrial cells, and cervical mucus.

Factors that can affect the menstrual cycle

It is normal that the menstrual cycle can vary in length, intensity and regularity due to different factors. Some of the factors that can influence the cycle include:

  • Emotional or physical stress: Stress can alter hormone levels and affect the length of the menstrual cycle.
  • Changes in body weight: Both significant weight loss and weight gain can affect ovulation and cycle regularity.
  • Use of hormonal contraceptives: Hormonal contraceptive methods, such as pills, patches, or intrauterine devices, can influence the length and regularity of the menstrual cycle.
  • Underlying health problems: Some medical conditions, such as polycystic ovary syndrome (PCOS), can lead to irregular or absent cycles.
  • Hormonal changes during perimenopause: As a woman approaches menopause, hormone levels can fluctuate, which can lead to irregular cycles.


Each phase of the cycle has a specific purpose and is critical to the possibility of conceiving and maintaining a pregnancy. It is important for all women to understand and connect with their menstrual cycle, as it can be a valuable tool for monitoring their reproductive health. If you experience significant changes, irregular cycles or worrisome symptoms, it is advisable to consult a healthcare professional.

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