The risk of birth defects increases four-fold if the pregnant mother has diabetes, researchers say.

The Newcastle University study, published in the journal Diabetologia, analysed data from more than 400,000 pregnancies in North East England.

The risk of defects such as congenital heart disease and spina bifida were increased.

National guidelines already recommend having good control over blood sugar levels before trying to conceive.

Both Type 1 diabetes, which tends to appear in childhood, and Type 2 diabetes, often linked to diet, lead to problems controlling the amount of sugar in the blood.

This is known to cause problems in pregnancy, such as birth defects, miscarriage and the baby being overweight due to too much sugar.

There is concern that rising levels of diabetes, particularly Type 2, could make the issue worse.

Researchers analysed data from 401,149 pregnancies between 1996 and 2008 - 1,677 women had diabetes.

The risk of birth defects went from 19 in every 1,000 births for women without pre-existing diabetes to 72 in every 1,000 births for women with diabetes.

Their report said that sugar levels in the run-up to conception were the "most important" risk factor which could be