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Let It Bleed: Causes of Heavy Periods

In the developed world, girls now get their periods earlier, and women spend less time being pregnant and breast feeding on demand. This means that the average women can now expect to have more than 400 menstrual cycles in her lifetime (ESHRE, 2007). Even the use of most hormonal contraceptives (pill/patch/ring) will yield a monthly bleed. So it’s no wonder that women are so concerned when their cycles seem to be longer and heavier than usual.

To address the most-pressing question, “When should I be concerned? What is the medical definition of too much bleeding?”, there is a medical definition of “too-heavy periods”. If a woman is bleeding 80cc (2.7 ounces — about 1/3 of a cup) or more, that is excessive bleeding. Trying to measure exactly the amount of bleeding is difficult even in a research setting, much less in a home bathroom! Some general indications of excessive bleeding can include:

  • Saturating a maxipad or super tampon every 60-90 minutes for several hours
  • Passage of large clots (quarter sized or larger)
  • Significant bleeding for more than seven days

Probably the most important factor would be if your bleeding is heavy enough to interfere with your normal activities.

There are two major reasons for very prolonged/heavy periods: hormonal and what I call “structural”. Here at WebMD we get questions about prolonged and heavy bleeding just about every day, so it seems like a good time to share information about some of the causes of “too-heavy periods” and other types of abnormally heavy vaginal bleeding.

This week we’ll talk about hormonal causes, and next week some structural reasons.

So if your bleeds are too heavy, read on for some possible explanations.

Hormonal Causes

Hormonal causes are usually linked to missed or erratic ovulation. As you may know, in a normal cycle, estrogen is produced all month. Estrogen is responsible for building up the lining of your uterus so you have something to shed each month. In a normal cycle, progesterone production increases following ovulation. Progesterone “stabilizes” the uterine lining in preparation for a possible implantation of a new pregnancy. If you are not pregnant that month the levels of estrogen and progesterone fall, triggering the release of the uterine lining — your period.

So if you do not ovulate, the estrogen build up of the lining continues, but without the usual ovulation associated progesterone. Thus, the hormone levels don’t decline, and the lining stays up inside the uterus as a missed/late period. Alternatively the lining can begin to shed under its own weight, producing prolonged bleeding. After several months of missed periods, the lining of the uterus can become very thickened. Prolonged and heavy flows are not uncommon after months of missed flows.

Here’s another way to understand how inadequate progesterone production from missed ovulation can create too heavy a flow:  if the uterine lining is like grass or lawn, estrogen is like the fertilizer (creates a thickening of the lining), and progesterone is like the lawnmower (keeps the lining thin by three different mechanisms). This is why birth control pills (relatively progesterone dominant) bring about shorter, lighter periods. It is also why women who miss ovulation (no progesterone produced) are at a greater risk for acquiring a thicker lining in their uterus.

There are MANY causes for not ovulating including low thyroid, a benign pituitary growth (“adenoma”), or a problem with the hypothalamus. All of the stress-related causes of not ovulating (e.g., sudden increases in exercise, crash dieting, problems with relationships, financial worries, etc.) can be linked to the effects of stress hormones from the brain on the hypothalamus. Increased body weight may trigger hormone changes leading to polycystic ovarian syndrome (“PCOS”). A transient ovarian cyst can halt ovulation for a time.

Interestingly, in a totally healthy, non-stressed woman, there are two times of her life when she is likely to miss or have erratic ovulation. The first is within the first two years of starting to have periods. At this time the ovaries are still maturing. Estrogen is already being produced (hence the development of breasts), but regular ovulation may not have begun. One study (Apter, 1997) found only 41% of cycles had ovulation by three years after the start of menstruation. Thus, when a bleed does occur in younger women it may be erratic and very heavy. Once regular ovulation becomes established, cycles are more predictable and flows tend to be no more than 5-7 days in length. Generally cycles hit a peak of regularity by age thirty-five.

The second time in the life of a healthy, non-stressed woman when heavy/erratic bleeding returns is in one’s forties. At that time the ovary has “used up” or ovulated its best eggs. Ovulation becomes less frequent, and when ovulation occurs, less progesterone may be produced. Estrogen is still going strong so a thickened lining is building up, but it is not exposed to the “lawnmower” activity of progesterone. The trigger to shed the lining at monthly intervals may not be there. Result? The dreadful gushing bleeds of midlife. Additionally, there is an increased incidence of having a structural cause of heavy bleeding develop as one advances through her menstrual life.

There are treatments for each of the causes of heavy bleeding we have discussed. So if you or someone you know has episodes of heavy blood loss rather than a normal period, talk to your doctor  –  there are ways to stop going with the flow.

Read the series “Let It Bleed: Causes of Heavy Periods”

Have you had periods with heavy bleeding? Share your comments and questions with the Women’s Health Community.

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