What are normal and heavy periods?
About 1 in 3 women describe their periods as 'heavy'. However, it is often difficult to know if your periods are normal or heavy compared to other women. Some women who feel they have heavy periods actually have an average blood loss. Some women who feel they have normal periods actually have a heavy blood loss. Most of the blood loss (about 90%) usually occurs in the first three days with either normal or heavy periods.
The strict medical definition of blood loss during a period is:
- A 'normal' period is a blood loss between 20 and 60 ml (4-12 teaspoonfuls). Bleeding can last up to eight days, but bleeding for five days is average.
- A 'heavy' period is a blood loss of 80 ml or more. This is about half a teacupful or more. Menorrhagia means recurring heavy periods.
However, it is difficult to measure the amount of blood that you lose during a period. For practical purposes, a period is heavy if it causes one or more of the following.
- Flooding through to clothes or bedding.
- You need frequent changes of sanitary towels or tampons.
- You need double sanitary protection (tampons and towels).
- You pass large blood clots.
- If it stops you doing normal activities such as going out, working, or shopping.
What causes heavy periods?
The exact cause is not known in most cases This is called 'dysfunctional uterine bleeding'. In this condition the uterus (womb) and ovaries are normal. It is not a hormone problem. Ovulation is usually normal and the periods are regular. A chemical called prostaglandin may play a part. The amount of prostaglandin in the lining of the uterus is often higher than normal in women with heavy periods. The high level of prostaglandin may affect blood clotting within the uterus. Bleeding then takes longer than normal to stop.
Other causes These are less common. They include the following:
- Fibroids. These are benign (non-cancerous) growths in the muscle of the uterus. They often cause no problems, but sometimes cause symptoms such as heavy periods.
- Other conditions of the uterus such as endometriosis (see separate leaflet), infections, polyps, or a previous sterilisation ('tubal tie') may lead to heavy periods. Cancer of the lining of the uterus (endometrial cancer) is an uncommon cause. This occurs in a small number of women, usually over the age of 40.
- Hormone problems. Periods can be irregular and sometimes heavy if you do not ovulate every month. An underactive thyroid gland may possibly cause heavy periods.
- The IUD (Intrauterine Device or 'coil') sometimes causes heavy periods. However, a special hormone-releasing IUD can actually treat heavy periods (see below).
- Warfarin or similar medicines interfere with blood clotting. If you take one of these medicines for other conditions, it may have a side-effect of heavier periods.
- Blood clotting disorders are rare causes of heavy bleeding. Other symptoms are also likely to develop such as easy bruising or bleeding from other parts of the body.
- Obese women are more likely to have heavy periods than women of average weight.
If you stop taking the contraceptive pill it may appear to cause heavy periods. Some women become used to the lightmonthly bleeds that occur whilst on 'the pill'. Normal periods return if you stop the pill. These may appear heavier, but are usually normal.
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