Gestational diabetes occurs when your body can’t make the extra insulin needed during pregnancy. Insulin, a hormone made in your pancreas, helps your body use glucose for energy and helps control your blood glucose levels.

During pregnancy, your body makes special hormones and goes through other changes, such as weight gain. Because of these changes, your body’s cells don’t use insulin well, a condition called insulin resistance. All pregnant women have some insulin resistance during late pregnancy. Most pregnant women can produce enough insulin to overcome insulin resistance, but some cannot. These women develop gestational diabetes.

Being overweight or obese is linked to gestational diabetes. Women who are overweight or obese may already have insulin resistance when they become pregnant. Gaining too much weight during pregnancy may also be a factor.

Having a family history of diabetes makes it more likely that a woman will develop gestational diabetes, which suggests that genes play a role.