Pregnant women with diabetes are almost four times more likely to have a baby with a birth defect, according to new research.

Experts found a higher risk of infants suffering serious problems if women had Type 1 or Type 2 diabetes, compared to women without the condition.

The range of birth defects included problems with the nervous system (such as spina bifida), digestive, musculoskeletal and cardiovascular defects and urinary disease.

Women with diabetes had a 7% risk of a having a baby with a birth defect, compared to an average of around 2% in women without diabetes. The chance of a birth defect was lowest in women who had blood glucose levels within the normal range at the start of pregnancy.

Experts analysed data from more than 401,000 pregnancies of single babies, including 1,677 in women with diabetes, between 1996 and 2008.

For women with Type 1 diabetes, the chance of a birth defect was 82.2 per 1,000 pregnancies and 57.9 per 1,000 in women with Type 2, which is linked to unhealthy lifestyles and obesity. Overall, women with diabetes had a 3.8 times higher risk of having a baby with a defect.

The research, published in the journal Diabetologia, showed that blood glucose levels around the time of conception was the most important factor predicting risk of congenital anomaly.

It also found that women with diabetes had no higher risk of having a baby with a chromosomal abnormality such as Down's syndrome, and these conditions were excluded from the analysis. Diabetes that occurs during pregnancy, known gestational diabetes, was also excluded.

Dr Ruth Bell, the study's lead researcher, from Newcastle University and Newcastle's Regional Maternity Survey Office, said: "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. Any reduction in high glucose levels is likely to improve the chances of a healthy baby."

Around 300,000 people in the UK have Type 1 diabetes, which usually develops under the age of 40 and requires daily insulin injections. Another 2.6 million are diagnosed with Type 2, which is linked to unhealthy lifestyles and obesity. It is estimated there are also 850,000 people with undiagnosed Type 2.