Screening for Gestational Diabetes Mellitus

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.

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.