The researchers said the increase was likely tied to rising levels of diabetes and obesity in the United States.

Having diabetes before pregnancy poses a particular risk because it affects the developing foetus right from the start, they said.

"It is really important for women with diabetes to plan their pregnancies and seek advice from their healthcare provider before they become pregnant," said Dr. Jean Lawrence of healthcare provider Kaiser Permanente in Pasadena, California, whose study appears in the journal Diabetes Care.

"Women who have a difficult time controlling their blood sugar have a higher risk of miscarriage or stillbirth. They also have a high risk of having a baby with a birth defect," Lawrence said in a telephone interview.

Risks can affect next generation
"Offspring of women who have diabetes or are overweight or obese during pregnancy – these children are more likely to be obese, overweight or have diabetes in the future," she said.

Past studies have looked at the rate of gestational diabetes, a type of diabetes that typically develops in the second trimester of pregnancy and often goes away after a woman gives birth.

Lawrence and colleagues looked at both gestational diabetes and women who had type 1 diabetes, which is typically diagnosed in childhood, and type 2 or adult-onset diabetes, in which the body loses its ability to use insulin properly.

While there were twice as many births to women with diabetes in 2005 as there were in 1999, the number of women with gestational diabetes remained fairly stable.

Diabetes increased fivefold among 13- to 19-year-olds giving birth and doubled among women 20- and 39-year-olds giving birth.

Black, Hispanic, and Asian/Pacific Islander women were more likely to have diabetes before pregnancy than white women, the study found.

About 20.8 million Americans have diabetes, which causes about 5 percent of all deaths globally each year. Most have type 2, which is closely linked to a obesity and lack of exercise. Type 1 diabetes is a so-called autoimmune disorder, caused when the body mistakenly destroys the pancreatic cells that make insulin.

"With the increasing prevalence of diabetes and obesity in society, it is very important that we start addressing this issue," Lawrence said.