What Causes Gestational Diabetes?

Medically Reviewed by Traci C. Johnson, MD on March 03, 2023
2 min read

Gestational diabetes is high blood sugar that you get only when you're pregnant. The word "gestational" means the time when the baby grows in the womb. In the U.S., it's estimated that 6 out of every 100 pregnant women have this disease. You can get it even if you didn't have diabetes before your pregnancy.

Good blood sugar control is important for your health and your baby’s. The first step in managing it is to understand what causes gestational diabetes.

When you eat, your body breaks down carbohydrates from foods into a sugar called glucose. The sugar goes into your bloodstream. From there, it travels to your cells to give your body energy. An organ called the pancreas makes a hormone called insulin, which helps move sugar into your cells and lower the amount in your blood.

During pregnancy, the placenta -- the organ that feeds and delivers oxygen to your baby -- releases hormones that help your baby grow. Some of these make it harder for your body to make or use insulin. This is called insulin resistance.

To keep your blood sugar levels steady, your pancreas has to make more insulin -- as much as three times more than usual. If it can't make enough extra insulin, your blood sugar will rise and you'll get gestational diabetes.

You may be more likely to get this disease if:

  • You were overweight before you got pregnant; extra weight makes it harder for your body to use insulin.
  • You gain weight very quickly during your pregnancy
  • You have a parent, brother, or sister with type 2 diabetes
  • Your blood sugar levels are high, but not high enough for you to be diagnosed with diabetes; this is called prediabetes.
  • You had gestational diabetes in a past pregnancy
  • You are over age 25
  • You gave birth to a baby weighing more than 9 pounds
  • You had a baby who was stillborn
  • You have a condition called polycystic ovary syndrome (PCOS)
  • You're African-American, American Indian, Hispanic, or Pacific Islander

Gestational diabetes usually starts in the beginning of the third trimester. However, if you have some risk factors, your doctor may recommend an early glucose test around the end of the first trimester. It is repeated again between 24-28 weeks of pregnancy, and if you test negative then, you won't be tested again. For the test, a laboratory technician will check your blood sugar after you drink a sugary drink.

Work with your doctor to lower your blood sugar during pregnancy. Depending on your test results, this might mean diet changes or medicine. When you keep your blood sugar under control, your baby will be less likely to have diabetes, be born at a heavier-than-normal weight, or have other health problems.