How Gestational Diabetes Is Diagnosed

Routine checks during pregnancy are important for a diagnosis

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Gestational diabetes is a type of diabetes that occurs during pregnancy and typically resolves after the baby is born. Routine screenings test for gestational diabetes during pregnancy, between 24 and 28 weeks. People at increased risk or with risk factors for type 2 diabetes may need to be tested earlier.

These screenings are important because symptoms of gestational diabetes are sometimes undetectable. Yet, gestational diabetes causes high blood sugar that will harm the pregnant person and fetus if left untreated.

This article will discuss how gestational diabetes is diagnosed, including lab tests and ruling out other causes (differential diagnosis).

Pregnant person checking blood sugar with a glucometer

Guido Mieth / Getty Images

Self-Checks/At-Home Testing

All pregnant people will be screened for gestational diabetes. Therefore self-checks and at-home testing are not typically utilized.

Gestational diabetes is a type of diabetes that first occurs during pregnancy and typically resolves after the baby is born. If you have an increased risk of developing diabetes or are experiencing symptoms of diabetes, you may need to be screened earlier.

There usually are no symptoms. However, they may include:

  • Increased hunger or thirst
  • Frequent urination
  • Nausea, feeling sick to your stomach, and vomiting
  • Blurry vision
  • Weight loss without changing eating habits or activity levels

Nonspecific Symptoms

Many of the symptoms of gestational diabetes mimic symptoms experienced during pregnancy, such as increased urination. Make sure you reach out to a healthcare provider if you are concerned about symptoms.

If you have risk factors for diabetes, such as a family history, obesity, an older maternal age, or a previous gestational diabetes diagnosis, a healthcare provider may recommend testing for prediabetes or diabetes at your first prenatal visit using diagnostic tests.


Gestational diabetes is diagnosed using one of two methods, either a two-part glucose challenge or a one-part challenge.

The two-part challenge requires you to drink 50 grams of a sugary drink (you do not need to be fasting). One hour after drinking the beverage, your blood is drawn

The blood glucose levels should be less than a number specified by the lab, which may be from 130 to 140 milligrams per deciliter (mg/dL). If they are higher, you will need to return for the second part of the test another day.

The next test, the oral glucose tolerance test (OGTT), requires you to drink a beverage that contains 100 grams of sugar (glucose). You must fast for this test. Blood is taken at hours one, two, and three.

A diagnosis of diabetes can be made when two or more of your values are higher than the reference range found below:

  • After fasting: 95 mg/dL or 5.3 millimoles per liter (mmol/L)
  • After one hour: 180 mg/dL (10.0 mmol/L)
  • After two hours: 155 mg/dL (8.6 mmol/L)
  • After three hours: 140 mg/dL (7.8 mmol/L)

75-Gram Glucose Tolerance Test

This is the one-part version. It is similar to the 100-gram test but is shorter in duration. You must arrive for the test after havng fasted. During this test, you will drink a beverage that contains 75 grams of sugar. Next, blood levels are drawn every 60 minutes for two hours.

Gestational diabetes is diagnosed when any of the following glucose values are met or are higher:

  • After fasting: 92 mg/dL (5.1 mmol/L)
  • After one hour: 180 mg/dL (10.0 mmol/L)
  • After two hours: 153 mg/dL (8.5 mmol/L)

Differential Diagnosis

Gestational diabetes develops during pregnancy and typically resolves when the baby is born. It is important to note that although the symptoms are the same, it is very different from type 1 and type 2 diabetes.

People with type 1 and type 2 diabetes who get pregnant can still have healthy pregnancies and babies by controlling their blood sugar, but unlike with gestational diabetes, their diabetes won't go away once the baby is born.

In addition, sometimes a person may get pregnant with preexisting prediabetes or type 2 diabetes that has been undiagnosed. If a healthcare provider suspects this is the case, they will usually test for these conditions at the first prenatal visit.

People who have been diagnosed with gestational diabetes during pregnancy are at increased risk of developing type 2 diabetes later in life. Therefore, testing for prediabetes or diabetes four to 12 weeks after delivery using the 75-gram oral glucose tolerance test and appropriate nonpregnancy diagnostic criteria is recommended.

If you have yet to conceive, you may assess your risk for prediabetes and type 2 diabetes using the Centers for Disease Control and Prevention (CDC) Prediabetes Risk Assessment Test and the American Diabetes Association Type 2 Diabetes Risk Assessment Test,


Gestational diabetes occurs during pregnancy and is screened for between 24 and 28 weeks of gestation using one of two diagnostic tests. Your healthcare provider may recommend that you receive testing earlier if they suspect you have had diabetes before pregnancy or if you have multiple risk factors,

Most of the time, there are no symptoms with gestational diabetes, but if you feel something is wrong, be sure to contact a healthcare provider.

Frequently Asked Questions

  • Can you prevent gestational diabetes?

    Preventing gestational diabetes is possible for some people, but not all. Certain people may have many risk factors and not develop it, while others do not have the same risk factors and do develop gestational diabetes.

    Participating in regular physical activity, adopting a healthy eating plan by eating fruits and vegetables, and limiting sugary beverages, refined grains, and too much animal protein can reduce the risk.

    In addition, lower rates of gestational diabetes are found in people who maintain a healthy body weight prior to pregnancy, get adequate sleep, and don't smoke.

  • What are the tests used to diagnose gestational diabetes?

    There are currently two different tests used to diagnose gestational diabetes. The two-part oral glucose tolerance test, includes drinking a 50-gram glucose beverage. If results are abnormal, a second 100-gram test is performed another day. Or, a one-part 75-gram glucose tolerance test is used.

  • How do you treat gestational diabetes?

    If you've been diagnosed with gestational diabetes, you should receive education from a certified diabetes care and education specialist and your healthcare provider to come up with an individualized treatment plan that keeps your blood sugars in a safe range for you and your baby. Your goal is to get your blood sugar levels equal to those of pregnant people who do not have diabetes.

    Treatment may include dietary changes, exercise, and testing blood sugar regularly. If blood sugars are not in a safe range, insulin may be needed. Taking insulin does not mean you've failed yourself or your baby. It means that your body needs some extra support during this time.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Diabetes Association. Classification and diagnosis of diabetes: standards of medical care in diabetes—2020. Diabetes Care. 2020;43(Supplement_1):S14–S31. doi:10.2337/dc20-S002

  2. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms and causes of gestational diabetes.

  3. Zhang C, Rawal S, Chong YS. Risk factors for gestational diabetes: Is prevention possible? Diabetologia. 2016;59:1385-1390. doi:10.1007/s00125-016-3979-3

  4. American Diabetes Association. Gestational diabetes: treatment and perspective.

By Barbie Cervoni MS, RD, CDCES, CDN
Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist.