Diagnosis of Gestational Diabetes
En Español (Spanish Version)

If you are at high risk of developing gestational diabetes (for example, obese, prior history of gestational diabetes, family history of diabetes), your doctor may recommend that you undergo glucose testing at your first prenatal visit. If your initial test is negative, you will be tested again later in your pregnancy.

If you are at an average risk of developing gestational diabetes, your doctor will do a screening test between 24-28 weeks of gestation.

There are different tests that can be used to diagnose gestational diabetes. These tests measure the level of glucose in your blood.

Glucose Tolerance Test
If your doctor has ordered the 100 gram glucose tolerance test, you will need to follow special dietary restrictions:

  • Three days before the test, eat a diet that contains at least 150 grams of carbohydrates a day.
  • For 10-14 hours before the test, do not eat or drink anything, except water.
The test is usually done in the morning in your doctor’s office. First, a blood sample is drawn to measure your fasting blood glucose level. Next, you will drink a glucose drink that contains 100 grams of glucose. Blood samples are drawn every hour for three hours after you finish the drink.

The diagnostic values used by the American Diabetes Association are as follows:

TimeBlood glucose valuesFasting95 mg/dL (5.3 mmol/L)1 hour180 mg/dL (10 mmol/L)2 hours155 mg/dL (8.6 mmol/L)3 hours140 mg/dL (7.8 mmol/L)
If two or more of your blood sugar levels are higher than the diagnostic blood glucose values, you have gestational diabetes. Once you have been diagnosed with gestational diabetes, your doctor will work with you to develop a treatment plan.

Other Tests
In addition to the above screening tests, additional tests may include:

  • HbA1c test (shows average glucose levels the past 2-4 months)
  • Urine tests
  • Thyroid function tests
  • Tests to monitor the fetus (for example, ultrasound)



References:
Gestational diabetes mellitus (GDM). EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated July 11, 2012. Accessed August 17, 2012.

Screening and diagnosis of gestational diabetes mellitus. Committee Opinion No. 504. American College of Obstetricians and Gynecologists. Obstet Gynecol. 2011;118:751-753.

What I need to know about gestational diabetes. National Diabetes Information Clearinghouse (NDIC) website. Available at: http://diabetes.niddk.nih.gov/dm/pubs/gestational/#7. Updated December 6, 2011. Accessed August 17, 2012.

Last Reviewed September 2013



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