Screening for Gestational Diabetes

Who Should be Screened for Gestational Diabetes?

All pregnant women should be screened for gestational diabetes, except those deemed by the American Diabetes Association to be at very low risk.

These patients at low risk include women meeting all of the following characteristics:

  • Age <25 years
  • Weight normal before pregnancy
  • Member of an ethnic group with a low prevalence of gestational diabetes
  • No known diabetes in first-degree relatives
  • No history of abnormal glucose tolerance
  • No history of poor obstetric outcome


When Should You be Screened for Gestational Diabetes?

Screening for gestational diabetes is usually done between 24 and 28 weeks of pregnancy. Screening can be done earlier in the pregnancy if there are risk factors for gestational diabetes, such as:

  • A history of gestational diabetes in a previous pregnancy
  • Obesity
  • Glucose (sugar) in urine
  • A strong family history of diabetes


The Gestational Diabetes Screening Test

There is no worldwide standard for screening and diagnosis of diabetes during pregnancy.  The most popular approach in the US is a  two stage screening test for gestational diabetes. Only those whose numbers are out of range in the first test need to continue to the second test.

Gestational Diabetes ScreeningThe First Test

On the day of the screening test you can eat and drink normally. You will be given 50 grams of glucose, usually in the form of a specially formulated orange or cola drink. You should drink the entire amount within a few minutes. One hour later, you will have a blood test to measure your blood sugar level.

If your blood sugar level is higher than normal, you will need another test to know confirm that you have gestational diabetes.  Most doctors and nurses consider your blood sugar level to be high if it is more than 130 to 140 mg/dL (7.2 to 7.7 mmol/L).

If your blood sugar level is higher than 200 mg/dL (11.1 mmol/L), then you have gestational diabetes.


Gestational Diabetes ScreeningThe Second Test

The second test for gestational diabetes is called an oral glucose tolerance test (OGTT).  It is done by measuring your blood sugar level before you eat anything in the morning (fasting), then again one, two, and three hours after you drink a glucose drink that contains 100 grams of glucose (twice the amount in the one-hour test).

Similar to the one-hour test, this is usually in the form of a specially formulated orange or cola drink.

Gestational diabetes is diagnosed if you have two or more blood sugar values above the following levels:

  • Fasting: greater than 95 mg/dL (5.3 mmol/L)
  • One-hour: greater than 180 mg/dL (10 mmol/L)
  • Two-hour: greater than 155 mg/dL (8.6 mmol/L)
  • Three-hour: greater than 140 mg/dL (7.8 mmol/L)


Read more about Gestational Diabetes:

 Reviewed by Dr. Mariela Glandt, Feb. 2013


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