Diagnosing Gestational Diabetes

The body goes through dramatic changes during the 40 weeks of pregnancy. Some of these changes are perfectly in sync with carrying and developing the fetus, but other changes can be harmful to baby and mom. One such change is the development of gestational diabetes.

Gestational diabetes carries the same symptoms and problems as other forms of diabetes are not associated with pregnancy. The body loses the ability to effectively handle food sugars and insulin development when pregnant. The onset of gestational diabetes can lead to hyperglycemia, hypoglycemia, and complications with fetal growth and birth.

About 15-25% of pregnant women will have an elevated glucose level on the standard 1-hour glucose test.

Glucose screening during pregnancy

At your first visit, your doctor will determine if you are at risk for diabetes, and if there is a family history, you will usually get tested for diabetes right away. Without added risks, the diabetes screening will often occur during the 26th to 28th week of gestation.

For the preliminary glucose screening, called the glucose challenge screening test, you will have to drink a special liquid full of glucose. After 1 hour, you will have blood drawn and the levels of glucose in the blood will be recorded. Blood glucose levels will most often be the highest 1 hour after consuming a high sugar meal or drink.

  • A level below 140 mg/dL is usually considered normal
  • A level above 140 mg/dL is usually considered elevated
  • Some doctors consider levels above 130-135 mg/dL elevated 

About 15-25% of pregnant women will have an elevated glucose level on the 1-hour glucose test.

If this preliminary test is normal, you will be cleared of having any likelihood of gestational diabetes, unless urine testing shows some sign of glucose in the urine further into the pregnancy.

If this preliminary test is outside of normal ranges, you will have to undergo a 3-hour glucose tolerance test to verify if you have gestational diabetes.

The 3-hour glucose tolerance test

Unlike the preliminary 1-hour glucose test, the glucose tolerance test (GTT) requires 14 hours of fasting before the test can take place. After those 14 hours, a baseline sample of blood will be taken. This baseline will tell the doctor the fasting glucose level. Then you will have to drink a highly concentrated glucose solution and more blood will be taken every hour for the next 3 hours.

The 3-hour GTT consists of drinking 100g of glucose and having four blood samples drawn: fasting, and then 1, 2, and 3 hours after the drink.
Cutoff values for the 3-hour GTT are as follows (Sullivan criteria):

  • Fasting: 95 mg/dL
  • 1-hour: 180 mg/dL
  • 2-hours: 155 mg/dL
  • 3-hours: 140 mg/dL

What if I have gestational diabetes?

Gestational diabetes in pregnancy is treated in much the same manner as diabetes is treated when not pregnant. For the official diagnosis of gestational diabetes to come back, two of the three vials of blood drawn will have to measure outside of the normal blood glucose range.

If only one of the tests is abnormal, you will often undergo dietary changes for the duration of the pregnancy, and then undergo the glucose tolerance test later to completely rule out gestational diabetes.

If the official gestational diabetes diagnosis is made, a combination of dietary changes, insulin usage, and increased exercise will be used to control the blood glucose levels. You will have to test your blood sugar levels throughout the day and try to maintain healthy levels. After the baby is born, most mothers find gestational diabetes ends with the pregnancy.

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