If you have a prior history of gestational diabetes or polycystic ovary syndrome, or a 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 Challenge Test
The 50 gram glucose challenge test is usually done in the morning in your doctor’s office. You will drink a glucose drink that contains 50 grams of glucose. Your blood will be drawn 1 hour later.
Doctors use different screening tests and cutoff values to make a diagnosis. Generally, these values at 1 hour range from 130 mg/dL (7.2 mmol/L) to 140 mg/dL (7.8 mmol/L). If your blood glucose is abnormally high at 1 hour, you will need to take a 3-hour glucose tolerance test to comfirm the diagnosis.
In addition to the above screening tests, additional tests may include:
HbA1c test (shows average glucose levels the past 2-4 months)
Thyroid function tests
Tests to monitor the fetus (for example,
Screening and diagnosis of gestational diabetes mellitus. Committee Opinion No. 504. American Congress of Obstetricians and Gynecologists. Obstet Gynecol. 2011;118:751-753.
What I need to know about gestational diabetes. National Institute of Diabetes and Digestive and Kidney Diseases website. Available at: https://www.niddk.nih.gov/health-information/diabetes/types/gestational#7. Accessed September 12, 2017.
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