PREGNANT women are being warned not to eat for two after research showed that obese mothers who develop gestational diabetes while pregnant and put on more weight after giving birth are 43 times more likely to go on to develop diabetes than slim women.

The increasing prevalence of gestational diabetes parallels the worldwide epidemic of type 2 diabetes, the research published in Diabetologia (the journal of the European Association for the Study of Diabetes) said.

Gestational diabetes is a common pregnancy complication. Previous studies have shown that up to a third of women with type 2 diabetes have a history of gestational diabetes during pregnancy and as a result, women in that position are usually advised to control their weight after delivery.

In this study, researchers in the United States analysed 1,695 women who reported gestational diabetes from 1991 to 2001.

They found there were 259 cases of type 2 diabetes during up to 18 years of follow-up.

There was an increased risk of developing type 2 diabetes of 16 per cent for each increase of one unit in either their baseline body mass index (BMI) or most recent BMI.

They also found that each 11lb increment of weight gain after gestational diabetes development was associated with a 27 per cent higher risk of type 2 diabetes.

And women who had a BMI of 30 or higher and gained 5kg or more after gestational diabetes had a 43 times increased risk of developing type 2 diabetes compared with women who had a BMI of 25 or less at baseline and gained 5kg or less after gestational diabetes.

Researchers said these associations persisted across different categories of age, family history of diabetes, diet quality, physical activity and breastfeeding duration.

Janet Fyle, professional policy advisor at the Royal College of Midwives, said the findings highlight the need to dispel the myth about eating for two during pregnancy.

She said: "This research underlines the need for women to start their pregnancy in optimal health at a healthy weight and to maintain this during and after their pregnancy.

"It also shows the need for better information, education and support for women about the benefits of healthy eating during pregnancy: for example, we need to dispel the myth that women need to eat for two during pregnancy.

"It is important for women to realise that help is available for them from midwives and others, to manage their weight during pregnancy and to avoid gaining too much."