Scientists have taken a step closer to understanding why some women experience heavy periods.

Heavy menstrual bleeding affects around one-third of women and can have a major impact on the lives of those affected. Some may have to change their sanitary towels or tampons very frequently, or even use both, while others leak through their clothes and/or onto their beds.

In a small number of cases, a woman may need a blood transfusion and surgery.

Scottish scientists decided to look into this further. They collected 44 biopsies from the lining of women's wombs. None of these wombs had any structural abnormalities.

Women who bled more than 80ml during one period were considered to have heavy periods.

The study found that those with heavy periods tended to bleed for an average of six days compared to those with normal periods, who bled for four days. This indicates that heavy bleeding occurs because the lining of the womb repairs slowly.

The scientists also looked at the role of a particular group of genes that are known to have an essential role in normal cell growth and tissue repair. They found that women with heavy periods had lower levels of the molecules linked with these genes.

"Heavy periods are very common and massively debilitating for the women that have them. Our results are exciting as it helps us to understand what goes wrong at the cell and molecular level in the womb lining," noted lead scientist, Dr Jacqueline Maybin, of the University of Edinburgh.

The team plans to continue its studies in this area.

"Ultimately, we want to develop novel treatments that are more effective and have fewer side-effects than those currently available," Dr Maybin added.

Details of these findings were presented at the Society for Endocrinology Annual BES Conference in Liverpool in the UK.