If you are trying to conceive, it is worth your while to track the length of your menstrual cycle. This is because the length of your cycle can provide important clues as to the overall health of your reproductive system.

A cycle includes far more than just a menstrual period; it involves complex coordination of hormonal and physical changes in the female reproductive system, especially the ovaries and uterus. It is this cyclical sequence of changes that are required in order to conceive and maintain an early pregnancy.

The three phases of the menstrual cycle include:

  1. The follicular phase - During the follicular phase, egg-containing follicles are matured and ready for ovulation. This is also when menstruation occurs.
  2. Ovulation - Ovulation involves the release of a mature egg from one of the ovaries, and normally, it occurs around 14 days after the start of the previous menstrual period.
  3. The luteal phase - During the luteal phase, the uterine lining or the endometrium prepares itself for receiving and nurturing a pregnancy which may occur in case the egg released during ovulation gets fertilized by a sperm. If pregnancy does not occur, the endometrium is shed off as the menstrual bleeding, more commonly known as a period.

What is a regular menstrual cycle?

A Menstrual cycle is considered normal when:

  • Your period occurs every 21 to 35 days (with an average of 28 days in most women).
  • The volume of bleeding is not excessive. The average amount of blood loss per day is 3 to 5 pads or tampons (approximately 30 to 40 ml per cycle).
  • The normal duration of menstrual bleeding is between 2 and 7 days.

What is an irregular menstrual cycle?

A menstrual cycle is considered abnormal if it is:

  • Longer than 35 days
  • Shorter than 21 days
  • Anovulatory (without the release of the egg)
  • Absent (no bleeding occurs)
  • Infrequently or irregularly occurring
  • Excessive or scanty in quantity, or includes spotting between periods

During the extremes of reproductive age, longer menstrual cycles and irregular patterns of menstrual bleeding are common. Menarche, the first occurrence of menstruation, is followed by approximately 5 to 7 years of increasing regularity as cycles shorten to reach a more consistent pattern.

The highest incidence of cycles without the release of an egg is under age 20 and over age 40, until menopause (the cessation of menses).

How do you determine the length of a menstrual cycle?

The first day of a menstrual cycle is considered to be the first day of bleeding during a period. The length of a menstrual cycle is from this first day of bleeding until the day before to the next period; the cycle resets back to day 1 with the start of the next period.

The length of a menstrual cycle varies from woman to woman. The length is primarily determined by the duration of the follicular phase, and it is completely normal for this portion of the cycle to vary in individual women. The luteal phase is remarkably constant in duration for each woman, with an average of 14 days.

How does the length of a menstrual cycle impact fertility?

Regular menstrual cycles indicate that a woman is probably ovulating, which is essential for a woman’s fertility. Irregular periods can be a symptom that indicates there could be an underlying condition impacting the fertility of a woman.

Problems with ovulation that include infrequent or absent ovulation account for approximately 40% of all infertility cases. The common underlying endocrine cause for the symptom includes thyroid disorders and polycystic ovary syndrome (PCOS).

Studies have shown that the chances of pregnancy occurring in women with irregular menstrual cycles are lower than those with normal cycles, and they also face an increased chance of having early pregnancy miscarriages.

In addition, timing sexual intercourse for a woman's fertile window may be difficult when menstrual cycles are of variable length and inappropriate timing may partially explain the subfertility seen in irregularly menstruating women.

What can cause an irregular menstrual cycle?

  • Menstrual irregularities are usually a symptom of hormonal imbalance including thyroid disorders and polycystic ovary syndrome (PCOS), which often lead to ovulation disorders.
  • Other factors like stress, extreme weight loss or gain, over-exercising, certain drugs and underlying medical conditions (e.g. anemia) can impact a menstrual cycle.
  • Structural abnormalities of the reproductive system including fibroids, polyps, or scar tissue, can be seen in some cases.
  • Normal changes in the later reproductive years where the better egg-containing follicles respond earlier in life, leaving the lesser follicles for later. This is reflected in the decrease in fertility that occurs with aging.

Tracking menstrual cycles and charting basal body temperature (BBT) can provide clues to the health of a menstrual cycle. The following conditions occur when the length of a cycle or the volume of menstrual bleeding are off.

Short Menstrual Cycles (Polymenorrhea)

What is: The cycle duration is less than 21 days. These short cycles increase the frequency of periods experienced.

Causes: The luteal phase is shortened the early a degeneration of the corpus luteum (the follicle after the egg is released) which supports this phase by releasing the hormone progesterone. An earlier withdrawal of progesterone causes bleeding to start earlier.

How it impacts fertility? Even if the egg is released and fertilized, the uterine lining is not receptive due to poor support from the corpus luteum. A fertilized egg would not be able to properly implant within the uterine lining. This is often called a luteal phase defect (LPD).

Treatment: The luteal phase is supplemented with progesterone medications.

Long Menstrual Cycles (Oligomenorrhea)

What it is: An increase in the cycle duration to more than 35 days. This means more than 35 days without experiencing a period. This also reduces the total number of periods experienced.

Causes: The usual cause is ovarian dysfunction, causing disorders of ovulation, i.e. the timely release of the mature egg. This dysfunction prolongs the follicular phase of the cycle, which effectively prolongs the entire cycle. Hormonal imbalances including thyroid disorders and polycystic ovary syndrome (PCOs) are common underlying causes for long cycles.

How it impacts fertility? Longer cycles reduces the frequency of ovulation and the number of opportunities to conceive. Without the release of a mature egg, fertilization and therefore pregnancy is not possible. Even if a woman has some cycles that are regular in between long cycles, the probability of conception decreases significantly.

Treatment: Ovulation inducing medications are used over a number of months in an attempt to regularize the cycles.

Prolonged or Heavy Menstrual Bleeding (Menorrhagia)

What it is: Menstrual bleeding from 7 to 14 days, with a blood loss of 60 ml to 80 ml.

  • In puberty and before menopause, menorrhagia is common.
  • Underlying severe medical conditions, including some blood disorders including anemia and some blood clotting and bleeding disorders.
  • Uterine causes like fibroids and polyps, infections of the pelvic organs, and some diseases like endometriosis.
  • An imbalance of other hormones like thyroid and prolactin hormones.
  • The use of an intrauterine device (IUD) can sometimes cause menorrhagia in some patients.
How it impacts fertility? A uterine lining that is not receptive to a fertilized egg is a cause of infertility as the fertilized egg cannot properly implant within the uterine lining.

Treatment: Treatment depends on the cause of the condition and factors like the woman’s age and desire for future fertility. Hormone therapy and a surgical procedure of curettage help some women. However, more radical treatments of a hysteroscopic endometrial ablation or a hysterectomy may be needed in some.

Scanty or Light Menstrual Bleeding (Hypomenorrhea)

What it is: A menstrual disorder with regularly timed, but scant or light menstrual bleeding.


  • Asherman’s Syndrome, a condition that causes variable degrees of scarring of the uterine lining and within the cavity.
  • Structural abnormalities of the reproductive tract such as fibroids, polyps, or scar tissue
  • Hormonal imbalances like hypothyroidism and hyperprolactinemia.

How it impacts fertility? Being regularly timed, it indicates that the controlling pituitary and ovarian hormones are normal in most cases. Hypomenorrhea does not necessarily mean infertility, and it is possible that conception could occur. However, the underlying cause of scarred or improperly developed uterine lining, or a hormonal imbalance could lead to miscarriages.

Treatment: Hypomenorrhea due to structural abnormalities of the reproductive tract such as fibroids, polyps, or scar tissue often can be treated during hysteroscopic surgery. If the underlying cause is related to medical or hormonal problems, then the appropriate medical treatment is often effective in reversing the problem.

Lack of Menstrual Bleeding (Amenorrhea):

What it is: Primary amenorrhea is the non-appearance of the menarche, the onset of menstruation. Secondary amenorrhea is the condition when there is no menstrual bleeding for at least 3 menstrual cycles, in a woman who had normal cyclic bleeding, and is not pregnant.

Causes of Secondary Amenorrhea:

  • A defect in the Hypothalamus-pituitary axis, the hormones of which control the menstrual cycle.
  • Ovarian causes like PCOS and premature menopause.
  • Severe underlying medical conditions, and an imbalance of other hormones like thyroid and prolactin hormones.
  • Uterine causes, like complete scarring and fibrosis.

How it impacts fertility? Either anovulation, where ovulation does not occur, or a defective uterine lining that is not receptive to the fertilized egg, causing infertility.

Treatment: Treatment varies depending on the cause.