Diabetic pregnant women are almost four times more likely to give birth to an unhealthy baby than women without diabetes because higher blood sugar levels raise the risk of birth defects, according to researchers.

About one in 13 babies born to a woman with type 1 or type 2 diabetes is affected by a major birth defect, such as heart disease and spina bifida.

At the same time, the study authors also stressed that 12 out of 13 pregnant women with diabetes are likely to give birth to a healthy baby.

In contrast, one in 50 women without diabetes is at risk of giving a baby with physiological problems.

But they stressed that the vast majority of pregnancies in women with diabetes did not involve a birth defect.

The study, led by researchers at Newcastle University and the Regional Maternity Survey Office, looked at the outcomes of 401,149 pregnancies, including 1,677 pregnancies in women with diabetes, between 1996 and 2008 in the North of England.

Researcher Ruth Bell told the journal Diabetologia:

"The good news is that, with expert help before and during pregnancy, most women with diabetes will have a healthy baby... The risk of problems can be reduced by taking extra care to have the best possible glucose control before becoming pregnant."

"This study offers clear evidence that although women with diabetes might still have a higher risk of a birth defect, they can still do something positive to reduce that risk by carefully monitoring their blood glucose level and trying to reduce it if it is high," said Dr. Iain Frame, Director of Research for Diabetes UK.

While there have been earlier studies that concluded having diabetes increases the chance of birth defects, this recent study is one of the first to quantify the effect of glucose levels on risk.

Doctors at the charity Diabetes UK funded the study, reported by the Daily Mail.