by EBSCO Medical Review Board

Pregnant women who are at high risk may need to be screened right away. If the screening is negative, another test will be done between 24 and 28 weeks of gestation.

All other pregnant women will be given the screening test between 24 and 28 weeks of pregnancy.

A pregnant woman who already has diabetes does not need to be screened.

Screening Tests

A woman does not need to fast before the glucose screening test. A special glucose drink will be given. One hour later, blood glucose levels will be tested to look for changes.

Women who have a high blood glucose screening test may need to have a 3-hour glucose tolerance test. She will not be able to eat or drink for 8 to 14 hours before the test. Blood will be drawn before the test. A special glucose drink will be given. Blood will be drawn every hour for 3 more hours to look for changes.


American College of Obstetricians and Gynecologists Committee on Practice Bulletins—Obstetrics. Practice Bulletin No. 190: Gestational Diabetes Mellitus. Obstet Gynecol. 2018 Feb;131(2):e49-e64.

Gestational diabetes. American Diabetes Association website. Available at: Accessed January 14, 2020.

Gestational diabetes mellitus (GDM). EBSCO DynaMed website. Available at: . Updated December 18, 2019. Accessed January 14, 2020.

Revision Information