Menstrual Cycle

The monthly cycle of changes in the female reproductive system, including menstruation.

What is the Menstrual Cycle and How Does It Work?

The menstrual cycle is a natural process that occurs in the female reproductive system every month. It involves changes in the ovaries, the uterus, the hormones, and the vagina. The main purpose of the menstrual cycle is to prepare the body for pregnancy by releasing an egg and building up the lining of the uterus. If the egg is not fertilised by a sperm, the lining of the uterus is shed as blood through the vagina. This is called menstruation or a period.

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Hormonal control of the menstrual cycle

The menstrual cycle has four phases: the menstrual phase, the follicular phase, the ovulation phase, and the luteal phase. Each phase is influenced by different hormones that are produced by the brain and the ovaries. These hormones are:

  • Follicle-stimulating hormone (FSH): This hormone stimulates the growth and development of one or more follicles (fluid-filled sacs that contain immature eggs) in the ovaries.

  • Luteinizing hormone (LH): This hormone triggers the release of a mature egg from the dominant follicle in the ovary. This is called ovulation.

  • oestrogen: This hormone is produced by the developing follicles and helps to thicken and nourish the lining of the uterus. It also affects the cervical mucus, making it thinner and more slippery to help the sperm reach the egg.

  • Progesterone: This hormone is produced by the corpus luteum (the empty follicle that remains after ovulation) and helps to maintain and stabilize the lining of the uterus. It also affects the cervical mucus, making it thicker and more sticky to prevent infection and further sperm entry.

The length and timing of the menstrual cycle can vary from person to person and from month to month. The average cycle length is about 28 days, but it can range from 21 to 35 days or longer.

Phases of the menstrual cycle

The menstrual cycle is the first day of bleeding. The following is a general overview of what happens in each phase of the cycle:

  • The menstrual phase: This phase lasts for about 3 to 7 days and is marked by the shedding of the uterine lining as blood and tissue through the vagina. This is the period. The amount and colour of the blood can vary from light to heavy and from bright red to dark brown. Some people may experience cramps, bloating, mood swings, headaches, or other symptoms during this phase.

  • The follicular phase: This phase starts on the first day of the period and ends with ovulation. It lasts for about 10 to 22 days, depending on the cycle length. During this phase, the FSH levels rise and stimulate the growth of several follicles in the ovaries. 

Usually, only one follicle becomes dominant and continues to mature, while the others are reabsorbed by the body. The oestrogen levels also rise and cause the uterine lining to thicken and the cervical mucus to become more fluid and clear. This phase is also called the proliferative phase because the cells of the uterine lining multiply and grow.

  • The ovulation phase: This phase is the shortest and lasts for about 12 to 24 hours. It occurs around the middle of the cycle, usually 14 days before the next period. During this phase, the LH levels surge and trigger the release of the mature egg from the dominant follicle in the ovary. The egg then travels through the fallopian tube toward the uterus. This is the most fertile time of the cycle, as the egg can be fertilised by a sperm within 12 to 24 hours after ovulation.

    The cervical mucus is also at its most slippery and stretchy, allowing the sperm to swim more easily. Some people may feel a slight pain or discomfort in the lower abdomen, called mittelschmerz, during ovulation. Others may notice a slight increase in their basal body temperature or a change in their cervical position or texture.

  • The luteal phase: This phase starts after ovulation and ends with the onset of the next period. It lasts for about 12 to 16 days, regardless of the cycle length. During this phase, the corpus luteum produces progesterone and some oestrogen, which help to keep the uterine lining intact and ready for implantation. If the egg is fertilised by a sperm, it will implant in the uterine wall and start to produce human chorionic gonadotropin (hCG), a hormone that signals pregnancy.

    If the egg is not fertilised, the corpus luteum will degenerate and stop producing hormones, causing the uterine lining to break down and the cycle to start over. The progesterone levels also affect the cervical mucus, making it thicker and less hospitable to sperm. This phase is also called the secretory phase because the glands of the uterine lining secrete substances that nourish the potential embryo.

The menstrual cycle is a complex and dynamic process that involves many factors and feedback mechanisms. It can be influenced by various internal and external factors, such as stress, illness, medication, diet, exercise, age, and environmental factors.

Some people may experience irregularities or disorders in their menstrual cycle, such as heavy bleeding, missed periods, painful periods, premenstrual syndrome, or polycystic ovary syndrome. These conditions may have different causes and treatments and may affect the fertility and general health of the person. Therefore, it is important to consult a healthcare provider if you have any concerns or questions about your menstrual cycle.

Do you have problems with your menstrual cycle flow pattern? Talk to us today! We are a team of medical health professionals strictly focused on women's health care.

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