We don't know what causes gestational diabetes, but we have some clues. The placenta supports the baby as it grows. Hormones from the placenta help the baby develop. But these hormones also block the action of the mother's insulin in her body. This problem is called insulin resistance. Insulin resistance makes it hard for the mother's body to use insulin. She may need up to three times as much insulin.
Gestational diabetes starts when your body is not able to make and use all the insulin it needs for pregnancy. Without enough insulin, glucose cannot leave the blood and be changed to energy. Glucose builds up in the blood to high levels, called hyperglycemia.
Growing baby, growing impact
Gestational diabetes affects the mother in late pregnancy, after the baby's body has been formed, but while the baby is busy growing. Because of this, gestational diabetes does not cause the kinds of birth defects sometimes seen in babies whose mothers had diabetes before pregnancy.
However, untreated or poorly controlled gestational diabetes can hurt your baby. When you have gestational diabetes, your pancreas works overtime to produce insulin, but the insulin does not lower your blood glucose levels. Although insulin does not cross the placenta, glucose and other nutrients do. So extra blood glucose goes through the placenta, giving the baby high blood glucose levels. This causes the baby's pancreas to make extra insulin to get rid of the blood glucose. Since the baby is getting more energy than it needs to grow and develop, the extra energy is stored as fat.
This can lead to macrosomia, or a "fat" baby. Babies with macrosomia face health problems of their own, including damage to their shoulders during birth. Because of the extra insulin made by the baby's pancreas, newborns may have very low blood glucose levels at birth and are also at higher risk for breathing problems. Babies born with excess insulin become children who are at risk for obesity and adults who are at risk for type 2 diabetes.
CDC podcast
The Centers for Disease Control and Prevention (CDC) podcast, Gestational Diabetes and Women, tells expectant moms more about diabetes during pregnancy. Learn about managing gestational diabetes, its impact on your future health and what you can do to lower your risk for type 2 diabetes after you've had it.
Gestational diabetes is a type of diabetes that is first seen in a pregnant woman who did not have diabetes before she was pregnant. Some women have more than one pregnancy affected by gestational diabetes. Gestational diabetes usually shows up in the middle of pregnancy. Doctors most often test for it between 24 and 28 weeks of pregnancy.
Often gestational diabetes can be managed through eating healthy foods and regular exercise. Sometimes a woman with gestational diabetes must also take insulin.
Learn more about Diabetes Self-Management Education and Support Services
Problems of Gestational Diabetes in Pregnancy
Blood sugar that is not well controlled in a woman with gestational diabetes can lead to problems for the pregnant woman and the baby:
An Extra-Large Baby
Diabetes that is not well controlled causes the baby’s blood sugar to be high. The baby is “overfed” and grows extra-large. Besides causing discomfort to the woman during the last few months of pregnancy, an extra-large baby can lead to problems during delivery for both the mother and the baby. The mother might need a C-Section to deliver the baby. The baby can be born with nerve damage due to pressure on the shoulder during delivery.
C-Section (Cesarean Section)
A C-section is an operation to deliver the baby through the mother’s belly. A woman who has diabetes that is not well controlled has a higher chance of needing a C-section to deliver the baby. When the baby is delivered by a C-section, it takes longer for the woman to recover from childbirth.
High Blood Pressure (Preeclampsia)
When a pregnant woman has high blood pressure, protein in her urine, and often swelling in fingers and toes that doesn’t go away, she might have preeclampsia. It is a serious problem that needs to be watched closely and managed by her doctor. High blood pressure can cause harm to both the woman and her unborn baby. It might lead to the baby being born early and also could cause seizures or a stroke (a blood clot or a bleed in the brain that can lead to brain damage) in the woman during labor and delivery. Women with diabetes have high blood pressure more often than women without diabetes.
Low Blood Sugar (Hypoglycemia)
People with diabetes who take insulin or other diabetes medications can develop blood sugar that is too low. Low blood sugar can be very serious, and even fatal, if not treated quickly. Seriously low blood sugar can be avoided if women watch their blood sugar closely and treat low blood sugar early.
If a woman’s diabetes was not well controlled during pregnancy, her baby can very quickly develop low blood sugar after birth. The baby’s blood sugar must be watched for several hours after delivery.
5 Tips for Women with Gestational Diabetes
- Eat Healthy Foods
Eat healthy foods from a meal plan made for a person with diabetes. A dietitian can help you create a healthy meal plan. Learn more about diabetes meal planning. - A dietitian can also help you learn how to control your blood sugar while you are pregnant. To find a registered dietician near you, please visit The Academy of Nutrition and Dietetics website.
- Exercise Regularly
Exercise is another way to keep blood sugar under control. It helps to balance food intake. After checking with your doctor, you can exercise regularly during and after pregnancy. Get at least 30 minutes of moderate-intensity physical activity at least five days a week. This could be brisk walking, swimming, or actively playing with children.Learn more about physical activity during pregnancy » - Monitor Blood Sugar Often
Because pregnancy causes the body’s need for energy to change, blood sugar levels can change very quickly. Check your blood sugar often, as directed by your doctor. - Take Insulin, If Needed
Sometimes a woman with gestational diabetes must take insulin. If insulin is ordered by your doctor, take it as directed in order to help keep blood sugar under control. - Get Tested for Diabetes after Pregnancy
Get tested for diabetes 6 to 12 weeks after your baby is born, and then every 1 to 3 years.For most women with gestational diabetes, the diabetes goes away soon after delivery. When it does not go away, the diabetes is called type 2 diabetes. Even if the diabetes does go away after the baby is born, half of all women who had gestational diabetes develop type 2 diabetes later. It’s important for a woman who has had gestational diabetes to continue to exercise and eat a healthy diet after pregnancy to prevent or delay getting type 2 diabetes. She should also remind her doctor to check her blood sugar every 1 to 3 years.
Women who had gestational diabetes or who develop prediabetes can also learn more about the National Diabetes Prevention Program (National DPP), CDC-recognized lifestyle change programs. To find a CDC-recognized lifestyle change class near you, or join one of the online programs.
More Information
Gestational Diabetes and
Pregnancy [PDF – 1 MB]
View, download, and print this brochure about gestational diabetes and pregnancy.
For more information on gestational diabetes, visit the American Diabetes Association’s website.