Variations in Menstrual Periods

By OBOS Anatomy & Menstruation Contributors |

Often we think of periods as occurring once per month; in fact, the word “menstruation” is from the Latin word mensis, for “month.” While some of us do have periods that occur exactly every month, others have cycles that are longer or shorter. Counting from the first day of one period to the first day of the next, most cycles last between 23 and 36 days. For some, the variation can be even broader.

You may have consistently regular cycles (bleeding every 28 or 35 days, for instance), or your cycle may vary in length from one cycle to the next.

Hormonal contraceptives or breastfeeding may alter the length of your cycle or even stop them altogether. Cycles may change after a pregnancy, regardless of whether it ended in abortion, a miscarriage, or birth.

Most periods last between two and eight days, with four to six days being the average. The flow stops and starts during this time, though this is not always noticeable.

The fluid that flows from the vagina during the menstrual period includes much of the uterine lining that has built up during that cycle. In addition to blood (sometimes clotted) and endometrial cells, menstrual fluid contains cervical fluid and vaginal secretions. This mixed content is not obvious, since the blood colors the fluid red or brown.

The usual discharge for a menstrual period is about two to five tablespoons, though it often looks like more.

For more information, see Stages in the Menstrual Cycle.

Very Heavy Periods (Menorrhagia) and/or Irregular Bleeding

You may experience a very heavy period if you did not ovulate during a cycle. This happens to all of us occasionally and occurs more often in the teen years, during perimenopause, during times of stress, and after any pregnancy.

Heavy periods can also occur if you have fibroids, are using certain IUDs for birth control (the Mirena IUD actually reduces cramps and bleeding), or have an inherited bleeding disorder. The most common inherited bleeding disorder, von Willebrand disease (VWD), affects about one to two percent of the U.S. population and runs in families. While it is often difficult to diagnose, and there is no cure, VWD can be treated. 

Irregular bleeding — off-schedule menstrual flow — can also be caused by recurrently not ovulating, which can be age-related (again, more common in early teens and perimenopause), or from some health problems or severe stress.

Bleeding in early pregnancy, which may or may not progress to miscarriage, can sometimes be confused with a menstrual period and can be light or heavy.

Keeping a menstrual calendar can help you develop awareness of what a typical flow is for you (see Charting Your Menstrual Cycle). If you have very heavy periods and/or irregular bleeding, it’s a good idea to talk with a health-care provider, because these can signal serious health problems. For more information, see Abnormal Uterine Bleeding.

No Periods and Very Light or Skipped Periods

Primary amenorrhea is the condition of never having had a period by the latest age (16) at which menstruation usually starts.

Secondary amenorrhea is missing periods after having had at least one. Oligomenorrhea is infrequent, erratic periods.

Some causes of amenorrhea and oligomenorrhea are pregnancy; menopause; breastfeeding; heavy athletic training; emotional factors; stress; current or recent use of hormonal birth control methods; excessive dieting, anorexia, or starvation; use of some medications, including chemotherapy; obstruction or malformation of the genital tract; hormone imbalance; cysts or tumors; chronic illness; and chromosomal conditions.

Sometimes amenorrhea or oligomenorrhea is caused by a combination of several of these factors.