EH logo
Sexual Health

Menstrual cycle

The menstrual cycle is driven by the rise and fall of molecules in your body known as hormones.
October 19, 2023

Regular Menstrual cycle

A regular menstrual cycle is typically said to begin at menstruation. The first day of the period is counted as the first day of the menstrual cycle. Following periods, which may last from 3-7 days, the ovaries- 2 small structures on either side of the uterus start the development of ovarian follicles or eggs. At the same time, the uterus starts developing a lining which is then used to nourish a growing pregnancy. The menstrual cycle ends when this uterine lining sheds in absence of a pregnancy. The menstrual cycle thus basically helps your body prepare for a pregnancy. It is also called a period, menstruation, or a cycle.

What is the average length of a menstrual cycle?

The typical menstrual cycle lasts 28 days. But this may vary from person to person. Any regular cycle length between 21 to 35 days is considered normal.

What drives the menstrual cycle?

The menstrual cycle is driven by the rise and fall of molecules in your body known as hormones. At particular points during your menstrual cycle, the pituitary gland in your brain and your ovaries produce and release hormones that induce the organs of your reproductive tract- the ovaries and the uterus to respond and lead to these phases of the cycle:

The menstrual phase: This is the time when the lining of your uterus is shed out. This lining then comes out from your vagina (if a pregnancy has not occurred), leading to a ‘period’. It normally lasts from 3 to 7 days. Most individuals bleed for around 3-5 days, although a period that lasts 2-7 days is still considered normal.

The follicular phase: This phase begins with your periods and normally lasts for 14 days. A hormone called the Follicle Stimulating Hormone, or FSH, from the pituitary gland in the brain acts on the ovaries to induce it to start developing follicles or eggs. These growing follicles in turn secrete the hormone called Estrogen which is the predominant hormone in this phase. This estrogen helps the endometrium, or the lining of the uterus to grow. 

Ovulation: This is an event that typically occurs on the 14th day of a 28-day cycle. One of the growing follicles will produce a completely developed egg which then ruptures and is released from the ovary. This ovulation is triggered by another hormone called the Luteinizing hormone, or LH, from the pituitary. 

The luteal phase: This is the last phase of the menstrual cycle which lasts for 14 days, irrespective of the length of your cycle. (So ovulation always occurs about 14 days prior to your periods) After the egg is released from your ovary, it is caught by the Fallopian tubes through which it goes to your uterus. The ovulated egg leaves behind a mass of cells called the ‘Corpus Luteum’ in the ovary which produces the hormone Progesterone. This Progesterone helps to further strengthen the endometrium in the uterus, thus preparing the uterus for pregnancy. You get pregnant if the egg is fertilized by a sperm and implants in the endometrium that has been prepared in anticipation of a pregnancy. If no pregnancy occurs, the corpus luteum degenerates after 14 days, estrogen and progesterone levels fall, and the endometrium or the thick uterine lining then sheds and is discarded during the menstrual period.

Symptoms of a menstrual cycle disorder include:

  • Your menstrual cycles are erratic.
  • You've been bleeding for more than seven days.
  • Your menstrual cycles are fewer than 21 days apart or over 35 days apart.
  • You bleed in between your menstrual periods.
  • You are bleeding heavier than normal.
  • You've skipped periods or your periods.

Each woman's menstrual cycle is unique. It's essential to become acquainted with your cycle, including when you get your periods and how long they last. What is normal for you may not be normal for someone else. Keep an eye out for any changes and notify your medical professional.