How Do I Know If I Have Gestational Diabetes?

What have you heard about Gestational Diabetes? If you’re just curious, have a history of this, or just simply want more information, here we take a look at how diabetes during pregnancy is tested and diagnosed.

Doctors started seeing really large babies when they were born, and after many studies, it became clear that higher sugars were causing the babies to gain too much weight. Criteria has been established to screen for diabetes during pregnancy to prevent larger babies and make delivery easier. It is now standard to check every pregnant woman for diabetes.

When will I be tested for gestational diabetes?

Testing for gestational diabetes (GDM) usually occurs between 24 and 28 weeks of pregnancy. If you have family members with diabetes or had GDM in previous pregnancies, there is an increased chance of developing gestational diabetes, and your doctor may test for diabetes during the first visit after you become pregnant.

How do doctors diagnose gestational diabetes?

Doctors use blood tests to diagnose gestational diabetes. You may have the A1c test, the glucose challenge test, and/or the oral glucose tolerance test, or all three. These tests show how well your body uses glucose.


The A1C test is a common blood test used to diagnose type 1, pre-diabetes and type 2 diabetes. It is usually done in the first trimester to catch higher sugars early.

The A1C test result reflects your average blood sugar level for the past two to three months. Usually, if the A1c is greater than 5.7% when it is drawn, we know that diabetes is or will be present with the pregnancy.

Glucose Challenge Test

You may have the glucose challenge test first, though it is becoming less common. Another name for this blood test is the glucose screening test. In this test, a healthcare professional will draw your blood 1 hour after you drink a sweet liquid containing glucose. You do not need to fast for this test. Fasting means having nothing to eat or drink except water. If your blood glucose is too high—140 or more—you may need to return for an oral glucose tolerance test while fasting. If your blood glucose is 200 or more, you may have type 2 diabetes.

Oral Glucose Tolerance Test (OGTT)

The OGTT measures blood glucose after you fast for at least 8 hours. First, a healthcare professional will draw your blood. Then you will drink the liquid containing glucose. You will need your blood drawn every hour for 2 to 3 hours for a doctor to diagnose gestational diabetes.

High blood glucose levels at any two or more blood test times—fasting, 1 hour, 2 hours, or 3 hours—mean you have gestational diabetes. Your health care team will explain what your OGTT results mean. Your health care professional may recommend an OGTT without first having the glucose challenge test.

It is important to catch gestational diabetes to prevent the baby from gaining too much weight and becoming too big. If this happens, the baby is put at risk for a vaginal delivery. Often times you must deliver the baby by Caesarean section (C-section).