Mothers with severe gum disease are far more likely to give birth prematurely, new research has found.

The link between the two is well-established, but experts from the US found that the worse the state of the pregnant woman's gums, the more likely a premature birth is.

The study of more than 2,000 pregnant women was presented at a periodontology conference in Washington DC on Saturday.

Women with any sort of periodontal disease may be up to seven times more likely to deliver a premature baby.

But those with "generalised periodontal disease" - meaning it affects more than 30% of the mouth, were at even worse risk.

Marjorie Jeffcoat, who led the survey, said: "We were amazed by these findings."

But she said that even those with relatively little gum disease were running the risk.

Risk of health problems

Babies born prematurely are at greater risk of a range of health problems.

These can even include developmental problems in later life.

And caring for premature babies in hospital in the first weeks of their lives costs the health service many thousands of pounds.

Dr Jeffcoat said: "Initial data tells us the best advice continues to be that women considering pregnancy have a periodontol screening and get any problems with their oral health under control before becoming pregnant."

She said that even women who are already pregnant could have scaling and other cleaning treatments.

Other major risk factors for periodontal disease include genitourinary infections, smoking and excessive alcohol drinking.

In the US, 25% of premature births happen without any known risk factor.