Diagnosis of Gestational Diabetes

Gestational diabetes mellitus (GDM) is diagnosed with a screening test that is given to all pregnant women. 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 Test

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.

3-Hour Glucose Tolerance Test

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.



Gestational diabetes. National Institute of Diabetes and Digestive and Kidney Diseases website. Available at: Accessed September 12, 2017.
Gestational diabetes mellitus (GDM). EBSCO DynaMed website. Available at: https://www.dyname.... Updated June 29, 2017. Accessed September 12, 2017.
Hillier TA, Pedula KL, et al. Excess gestational weight gain: modifying fetal macrosomia risk associated with maternal glucose. Obstet Gynecol. 2008;112:1007-1014.
2/5/2009 DynaMed Systematic Literature Surveillance: https://www.dyname.... Cheng YW, Chung JH, et al. Gestational weight gain and gestational diabetes mellitus: perinatal outcomes. Obstet Gynecol. 2008;112:1015-1022.
Last reviewed September 2018 by EBSCO Medical Review Board Beverly Siegal, MD, FACOG