Screening for Gestational Diabetes Mellitus

Am Fam Physician. 2004 Mar 1;69(5):1187-1188.

This clinical content conforms to AAFP criteria for evidence-based continuing medical education (EB CME). EB CME is clinical content presented with practice recommendations supported by evidence that has been systematically reviewed by an AAFP-approved source. The practice recommendations in this activity are available at http://www.ahrq.gov/clinic/serfiles.htm.

Case Study

MT is a 23-year-old woman visiting your office for her initial prenatal checkup. She has a family history of diabetes and is obese. MT developed gestational diabetes mellitus (GDM) during her previous pregnancy, and because she is concerned about having GDM, she asks if she should be tested.

Case Study Questions

1. According to the U. S. Preventive Services Task Force (USP-STF) recommendations, which one of the following statements should be considered in MT's care?

  • A. Clinicians should screen all pregnant women for GDM.

  • B. Screening combined with diet and insulin therapy does not reduce the rate of fetal macrosomia in women with GDM.

  • C. Screening for GDM substantially reduces neonatal morbidity and mortality.

  • D. Screening for GDM produces frequent false-positive results.

  • E. The 100-g, three-hour oral glucose tolerance test should be the initial screening test.

2. Which of the following characteristics place MT at increased risk for GDM?

  • A. Obesity.

  • B. Personal or family history of diabetes.

  • C. Age.

  • D. History of GDM.


1. The correct answer is D. Screening produces frequent false-positive results. The prevalence of GDM in average-risk women ranges from 1.4 to 2.8 percent, and fewer than one in five women with a positive glucose challenge test will meet criteria for GDM on an oral glucose tolerance test. Although the USPSTF found fair to good evidence that screening combined with diet and insulin therapy can reduce the rate of fetal macrosomia in women with GDM, they found insufficient evidence that screening for GDM substantially reduces important adverse health outcomes for mothers or their infants, including cesarean delivery, birth injury, or neonatal morbidity and mortality. Until better quality evidence is available, clinicians might reasonably choose not to screen at all or to screen only women at increased risk for GDM.

The optimal approach to screening and diagnosis is uncertain. Expert panels in the United States have recommended a 50-g, one-hour glucose challenge test (GCT) at 24 to 28 weeks of gestation followed by a 100-g, three-hour oral glucose tolerance test for women who screen positive on the GCT. However, different screening and diagnostic strategies are recommended by the World Health Organization and are commonly used outside North America.

2.The correct answers are A, B, and D. Maternal obesity (body mass index >25), family or personal history of diabetes, and a history of GDM are strongly associated with increased risk for GDM. Age greater than 25 also is a risk factor, but MT is 23. The prevalence of GDM among women with these risk factors ranges from 3.3 to 6.1 percent. Expert groups also have identified Hispanic, African American, American Indian, and South and East Asian groups as being at increased risk for GDM. However, using all of the above criteria would identify 90 percent of all pregnant women as being at increased risk for GDM. Although screening a high-risk population would improve the yield and reduce false-positive results, there is insufficient evidence that screening improves outcomes.


U.S. Preventive Services Task Force. Screening for gestational diabetes mellitus: recommendations and rationale. Accessed November 2003 at: http://www.ahrq.gov/clinic/3rduspstf/gdm/gdmrr.htm.

Brody SC, Harris RP, Lohr KN. Screening for gestational diabetes: a summary of the evidence for the U.S. Preventive Services Task Force. Obstet Gynecol. 2003;101:380–92.

Brody SC, Harris R, Whitener BL, et al. Screening for gestational diabetes: systematic evidence review no. 26 (Prepared by RTI-University of North Carolina at Chapel Hill Evidence-Based Practice Center under Contract No. 290-97-011). Accessed November 2003 at: http://www.ahrq.gov/clinic/serfiles.htm.

The case study and answers to the following questions about screening for gestational diabetes mellitus are based on the recommendations of the current U.S. Preventive Services Task Force (USPSTF), part of the Put Prevention into Practice program of the Agency for Healthcare Research and Quality (AHRQ). This recommendation was released in 2003. More detailed information on this subject is available in the Systematic Evidence Review, Summary of the Evidence, and USP-STF Recommendations and Rationale on the AHRQ Web site (http://www.ahrq.gov). The Summary of the Evidence and the USPSTF recommendation and rationale statement are available in print through subscription to the Guide to Clinical Preventive Services, Third Edition: Periodic Updates. To order, contact the AHRQ Publications Clearinghouse (800-358-9295).

This case study is part of AFP's CME. See “Clinical Quiz” on page 1039.

Copyright © 2004 by the American Academy of Family Physicians.
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