According to a California study, the number of pregnant women with pre-existing diabetes has more than doubled in seven years, the Associated Press reports. It appears that the expectant mothers who do not control their diabetes face an increased risk of miscarriage and stillbirth. Their newborns have a higher chance of being born with birth defects.

“These are high-risk pregnancies,” said Dr. Florence Brown, an expert on pregnancy and diabetes, quoted by the A.P. “All women with pre-existing diabetes need to plan their pregnancies,” he added.

“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,” said Dr. Jean Lawrence of healthcare provider Kaiser Permanente in Pasadena, California. “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 added, quoted by Reuters.

The researchers’ report focused on health records from 175,000 ethnically diverse women who gave birth in Kaiser hospitals in Southern California from 1999 to 2005. Diabetes increased fivefold among 13- to 19-year-olds giving birth and doubled among women 20- and 39-year-olds giving birth. Black, Asian and Hispanic women were more likely to have diabetes before pregnancy than white women, the study found.

Nearly 20.8 million Americans suffer from diabetes, which causes about 5% of all deaths globally each year. Most of them have type 2 diabetes, which is closely connected to obesity and lack of exercise.