What causes gestational diabetes? Hormones from the placenta help the baby grow, but they also make insulin work less well. The American Diabetes Association (ADA) says these hormones can block the mother's insulin, which leads to insulin resistance. Most bodies respond by making more insulin. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says gestational diabetes develops when the body cannot make enough extra insulin during late pregnancy, so blood sugar rises.
Key takeaways
- NIDDK says all pregnant women have some insulin resistance during late pregnancy. Gestational diabetes happens when the body cannot make enough extra insulin to overcome it.
- ADA says the exact cause is unclear, but hormones from the placenta play a central role.
- Weight before pregnancy, family history, and genes affect who gets it. NIDDK says people with overweight or obesity may already have insulin resistance when they become pregnant.
- The American College of Obstetricians and Gynecologists (ACOG) says gestational diabetes can also develop in people with no risk factors.
- The Centers for Disease Control and Prevention (CDC) says lifestyle changes before pregnancy may help prevent it, but you should not try to lose weight once you are pregnant.
How Gestational Diabetes Happens, Step by Step
Insulin is a hormone made in the pancreas. CDC says it acts like a key that lets blood sugar into your cells for energy. Here is what sources describe during pregnancy:
- The placenta makes hormones. ADA says these hormones support the baby's growth.
- Those hormones block insulin. ACOG says higher levels of pregnancy hormones can interfere with insulin. CDC adds that pregnancy weight gain also makes cells use insulin less well. This is called insulin resistance.
- The body needs more insulin. CDC says insulin resistance raises your body's need for insulin.
- Most bodies keep up. NIDDK says most pregnant women can make enough insulin to overcome insulin resistance.
- Some cannot. NIDDK says pregnant women who cannot make enough insulin during late pregnancy develop gestational diabetes.
ADA's 2026 guidance describes the timing. Early pregnancy can bring better insulin sensitivity and lower glucose levels. Insulin resistance then rises in the second and third trimesters. CDC says gestational diabetes usually develops around the 24th week, which is why screening often happens between 24 and 28 weeks.
Why Some People Get It and Others Do Not
Every pregnancy brings insulin resistance, so the question is why some bodies cannot keep up. NIDDK and CDC point to these factors:
- Insulin resistance before pregnancy. NIDDK says people with overweight or obesity may already have insulin resistance when they become pregnant. Pregnancy then adds more.
- Weight gain during pregnancy. NIDDK says gaining too much weight during pregnancy may also be a factor. ACOG says to talk with your ob-gyn about how much weight gain is best for you.
- Genes and family history. NIDDK says a family history of diabetes makes gestational diabetes more likely, which suggests genes play a role. See whether type 2 diabetes is genetic.
- Hormone conditions. CDC lists polycystic ovary syndrome (PCOS). Read more about PCOS and diabetes.
- A past pregnancy with gestational diabetes or a large baby. CDC lists both. ACOG says gestational diabetes greatly raises the risk of diabetes in a later pregnancy.
- Being less active. ACOG lists being physically inactive.
- Ethnic background. CDC says African American, Hispanic or Latino, American Indian, Alaska Native, Native Hawaiian, and Pacific Islander people are at higher risk. ACOG adds Asian women.
Our guide to gestational diabetes symptoms covers the full list of risk factors and how screening works.
Sometimes It Is Diabetes That Was Already There
Not every high reading in pregnancy is gestational diabetes. CDC says that if blood sugar is higher than normal early in pregnancy, you may have type 1 or type 2 diabetes instead. ACOG says some people diagnosed with gestational diabetes may have had mild diabetes before pregnancy without knowing it. For them, diabetes does not go away after birth.
ADA's 2026 guidance goes further. It says gestational diabetes often represents prediabetes or type 2 diabetes that was not diagnosed before, a form of inherited diabetes called MODY, or even type 1 diabetes that is starting to develop. This is one reason ADA recommends testing after birth.
Common Myths About What Causes Gestational Diabetes
"I ate too much sugar." None of the sources we reviewed list eating sugar as the cause. The main driver is placental hormones and how much insulin your body can make. What you eat does affect your blood sugar once you have gestational diabetes, which is why eating plans are part of treatment.
"It's my fault." ADA says the exact cause is unclear and there is still a lot that is not known. ACOG says it can develop in people with no risk factors at all. ADA also says that being diagnosed does not mean you had diabetes before pregnancy or that you will have it after birth.
"Only people with obesity get it." Weight raises the risk, but ACOG says anyone can get gestational diabetes during pregnancy.
"It means my baby will have diabetes." ACOG says children of people who had gestational diabetes have a higher risk of overweight and diabetes. A higher risk is not a diagnosis. ACOG advises telling your baby's doctor so your child can be checked as they grow. See whether kids can get type 2 diabetes.
Can Gestational Diabetes Be Prevented?
Sometimes, and mostly before pregnancy. CDC says that before you get pregnant, you may be able to prevent gestational diabetes with lifestyle changes. These include losing weight if you have overweight, eating a healthy diet, and getting regular physical activity.
ADA's 2026 guidance cites research that regular exercise during pregnancy was linked to 38% lower odds of gestational diabetes. ADA also cites a trial in which people with overweight or obesity and a past gestational diabetes pregnancy who lost weight before their next pregnancy had a lower chance of it coming back.
Two cautions matter here:
- Do not try to lose weight once you are pregnant. CDC says you need to gain some weight for your baby to be healthy. Ask your doctor how much weight gain is right for you.
- Ask before starting a new exercise plan. ADA advises working with your care team to find the safest level of activity during pregnancy.
If you had gestational diabetes before and are planning another pregnancy, ADA recommends testing for type 2 diabetes or prediabetes before conception, or before 15 weeks of pregnancy if you were not tested earlier. Our guide to how to prevent diabetes covers prevention steps outside pregnancy.
What Happens After Diagnosis
Gestational diabetes is treatable. ADA's 2026 guidance says 70% to 85% of people diagnosed under a common set of criteria can manage it with lifestyle changes alone. Some people need insulin. Our guide to how gestational diabetes is treated explains each step, and our diabetes and pregnancy guide covers every type of diabetes in pregnancy.
Frequently Asked Questions
What is the main cause of gestational diabetes?
The main cause is hormones from the placenta. ADA says these hormones can block the mother's insulin, leading to insulin resistance. NIDDK says gestational diabetes develops when the body cannot make enough extra insulin to overcome that resistance in late pregnancy.
Does eating sugar cause gestational diabetes?
None of the sources we reviewed list eating sugar as the cause. Gestational diabetes is driven mainly by placental hormones and how much insulin your body can make. Once you have it, what and when you eat does affect your blood sugar, so an eating plan is part of treatment.
Can you get gestational diabetes with no risk factors?
Yes. ACOG says gestational diabetes can develop in people with no risk factors. That is why ACOG says all pregnant women should be screened, usually between 24 and 28 weeks, or earlier for people at higher risk.
Is gestational diabetes caused by being overweight?
Weight is a risk factor, not the only cause. NIDDK says people with overweight or obesity may already have insulin resistance when they become pregnant, and pregnancy adds more. But ACOG says anyone can get gestational diabetes during pregnancy.
Can gestational diabetes be prevented?
Sometimes. CDC says lifestyle changes before pregnancy, such as losing weight if you have overweight, eating a healthy diet, and regular activity, may help prevent it. CDC also says not to try to lose weight once you are pregnant. Ask your care team what activity is safe for you.
When does gestational diabetes start?
CDC says gestational diabetes usually develops around the 24th week of pregnancy. ADA says insulin resistance rises in the second and third trimesters. That timing is why screening usually happens between 24 and 28 weeks.
References
- American Diabetes Association. “Gestational Diabetes.” Accessed October 2026.
- National Institute of Diabetes and Digestive and Kidney Diseases. “Symptoms & Causes of Gestational Diabetes.” Last reviewed May 2017. Accessed October 2026.
- Centers for Disease Control and Prevention. “Gestational Diabetes.” Accessed October 2026.
- Centers for Disease Control and Prevention. “Diabetes During Pregnancy.” Accessed October 2026.
- American College of Obstetricians and Gynecologists. “Gestational Diabetes.” Accessed October 2026.
- American Diabetes Association Professional Practice Committee for Diabetes. “15. Management of Diabetes in Pregnancy: Standards of Care in Diabetes—2026.” Diabetes Care. 2026;49(Suppl. 1):S321–S338. Accessed October 2026.
Next Steps
If you are planning a pregnancy, ask your care team about your risk and whether you should be tested early. If you are already pregnant, keep your scheduled glucose screening.
For adults with type 2 diabetes or prediabetes who want lifestyle education alongside clinical care, the Done With Diabetes™ program, a holistic approach to diabetes type 2, organizes learning about meals, movement, sleep, and stress. It is not designed to manage gestational diabetes or pregnancy. It does not diagnose or treat diabetes, interpret test results, change medicines, or replace your prenatal or diabetes care team.