Cycle Length

Definition - What does Cycle Length mean?

The cycle length of a woman’s menstrual cycle refers to the number of days her cycle takes to go from the beginning (the first day of menstruation) until the end (the last day before the next menstruation). It is, on average, 28 days in length, although it could range anywhere from 21 to 36 days in length. Being aware of her cycle length can allow a woman to pinpoint the day of ovulation and thereby determine the brief window when she is most likely to become pregnant.

FertilitySmarts explains Cycle Length

A woman’s menstrual cycle varies to some degree; some cycles are shorter while others are longer. If a woman’s cycle varies between 4 and 8 days from shortest cycle to longest cycle, this is considered regular. Variations of less than 4 days or more than 8 days are considered irregular. Women under 25 experience the most variability in the lengths of their cycles, while women ages 25-39 have the least variability. Past age 40 until menopause, a woman can expect slightly more variability.

The menstrual cycle can be thought of as two separate phases: the follicular phase, during which the ovaries prepare to release an egg into the fallopian tubes, and the luteal phase, during which the uterus wall thickens to potentially receive an embryo. The follicular phase can be anywhere from 12-25 days in length while the luteal phase is more consistent, at 12-14 days in length. Ovulation, the release of an egg from an ovary, occurs directly between the two phases.

Many things can cause menstrual cycles to become irregular. Stress, for example, can delay ovulation, which in turn delays menstruation (the luteal phase of the menstrual cycle is generally 12-14 days regardless of other influences). Other causes of irregular cycle lengths are eating disorders, extreme weight loss, excessive exercising, polycystic ovary syndrome (PCOS), premature ovarian failure, pelvic inflammatory disease (PID), and uterine fibroids.

If a woman’s follicular phase is short, less than 10 days in length (meaning ovulation occurs on or before day 10), this could mean that an immature egg was released. Usually, this means the egg can’t be fertilized or might have chromosomal abnormalities. If a women’s follicular phase is longer than 25 days, this could be a sign that the body is attempting to ovulate multiple times. This is common in women with PCOS, or could be a sign of stress. Fortunately, it usually doesn’t change the odds of conceiving or the viability of the egg released.

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