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The following things increase your chances of getting heavy periods. Doctors call them risk factors.

Women over age 40 are more likely than younger women to have heavy periods. In one study:¹

• 25 in 100 women aged 41 to 49 had heavy periods
• But only 15 in 100 women aged 31 to 35 did
• And less than 5 in 100 women aged 19 to 25 did.

One reason may be changes in women's hormones as they approach menopause (the time when their periods stop altogether).

As you near menopause, you are less likely to ovulate (when an egg is released from an ovary). Your body still makes the hormones estrogen and progesterone, although the amount of these will gradually get smaller and smaller. Because you get fewer periods, the lining of your womb can get very thick. So when your period starts, there is more blood than usual.

Also, as you get older, you are more likely to have fibroids in your womb. These growths are not cancer, but can cause heavy periods.

If you have heavy periods, ask your mother if she had (or has) them too. Some research suggests that this condition may be inherited. This means it may be passed on from parent to child through genes.

A study of identical twins (who have the same genes) showed that they had very similar blood loss during their periods. But the same wasn't true of non-identical twins (who don't have all the same genes).²

There is some evidence that women who've had children lose more blood during their periods than those who haven't. Women who've had more than three children seem to be most at risk.

But, since women who've had children are often older than women who haven't, it may be their age rather than the fact that they've had children that increases their risk of heavy periods.¹

Some research suggests that if you smoke, you are more likely to have problems with your periods, such as heavy bleeding, pain and bleeding between your periods. Your periods are also more likely to be long and irregular (the number of days between your periods varies a lot).^{3 4}

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.