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Brody S, Harris RP, Whitener BL, et al. Screening for Gestational Diabetes Mellitus [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2003 Feb. (Systematic Evidence Reviews, No. 26.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Screening for Gestational Diabetes Mellitus [Internet].

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1Introduction

Epidemiology of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance with the onset or first detection during pregnancy.1, 2 GDM occurs in 2% to 5% of all pregnancies, for approximately 135,000 cases annually in the United States. 1 Major risk factors for developing GDM include increasing maternal age, family history of diabetes, increased pregravid body mass index (BMI), and lack of pregravid vigorous exercise. 3

Observational data reveal that the prevalence of GDM in women with defined low-risk factors, such as being of white ethnic origin, less than 25 years old, and having a BMI less than 25 kilograms per meter of height squared (kg/m2), ranges from 1.4% to 2.8%.4-6 The prevalence of GDM in the low-risk group of adolescent or teenage pregnancies ranges from 1.2% to 1.8%.7-9 The prevalence of GDM in high-risk populations (those with risk factors such as obesity, family history of diabetes, certain ethnic groups) generally ranges from 3.3% to 6.1%.6,10,11

Pregnant women demonstrate a range of glucose intolerance, exemplified by normal to slightly or greatly elevated glucose levels. Physiologic changes during pregnancy impair peripheral insulin action, inducing a degree of glucose intolerance that increases as pregnancy progresses. In normal pregnancies, the fasting levels of glucose range from 60 milligrams per decileter (mg/dL) to 90 mg/dL; 1-hour and 2-hour postprandial levels of glucose are less than 140 mg/dL and 120 mg/dL, respectively. 1 Thus, pregnant women demonstrate a spectrum of glucose intolerance exemplified by prolonged postprandial hyperglycemia and hyperinsulinemia, but with mild fasting hypoglycemia.

Markedly elevated maternal glucose levels most often occur in women with pregestational diabetes. These pregnancies are at higher risk for multiple complications affecting both the mother and the fetus than are those among women without existing diabetes. Current therapy improves outcomes for both mother and fetus. 12

The point on the spectrum of glucose intolerance that defines "gestational diabetes" is controversial. No study has found a threshold that separates those with risk of complications from those with no risk.

Both additional risk of adverse health outcomes from the lower levels of maternal hyperglycemia associated with GDM, detectable primarily by screening in the third trimester, and the magnitude of the benefit from treating that risk are less certain than are data about women with pregestational diabetes. No well-designed randomized controlled trial (RCT) of screening for GDM has been completed, and thus the evidence for screening is indirect.

Prior Recommendations about Screening for Gestational Diabetes Mellitus

National groups disagree about whether to recommend screening for GDM (Table 1).1,13-17 The American Diabetes Association 17 and the Fourth International Workshop on Gestational Diabetes Mellitus, 16 for example, recommend selective screening (i.e., screening all women with risk factors and no glucose testing of women who do not meet specific criteria). In the mid-1990s, the US Preventive Services Task Force (USPSTF) and earlier the Canadian Task Force on the Periodic Health Examination concluded that the evidence was insufficient to recommend for or against routine screening.13,14 The USPSTF had also noted that "... Clinicians may decide to screen high-risk pregnant women on other grounds..."(p. 204). 14

Table 1. Key Prior Recommendations for Screening for Gestational Diabetes Mellitus.

Table

Table 1. Key Prior Recommendations for Screening for Gestational Diabetes Mellitus.

Despite no strong recommendations in favor of universal screening, a 1996 survey by the American College of Obstetricians and Gynecologists (ACOG) showed that 94% of 550 ACOG Fellows in office-based practice reported performing universal screening for GDM. 18 This pattern was seen even though ACOG made no definite recommendation in 1994, stating that "there are no data to support the benefit of screening...and further studies are needed on which to base a recommendation" (p.5). 19 At the same time, the ACOG guidelines stated that selective screening for GDM may be appropriate in some clinical settings (e.g., teen clinics) but that universal screening may be more appropriate in other settings (e.g., in those having a high background prevalence of type 2 diabetes and other risk factors). 18

The latest ACOG recommendation (issued in 2001), based primarily on consensus and expert opinion, stated that "although universal glucose challenge screening for GDM is the most sensitive approach, there may be pregnant women at low risk who are less likely to benefit from testing" (p. 534). 1 These recommendations were made "despite the lack of population-derived data supporting the benefit of making the diagnosis of GDM" (p. 526).

With the continuing controversy concerning the advisability of GDM screening, the RTI International-University of North Carolina Evidence-based Practice Center (RTI-UNC EPC) undertook this systematic evidence review (SER) to assist the USPSTF in reconsidering its previous conclusions and recommendation. We restricted the SER to screening for GDM in the third trimester of pregnancy, thus excluding both women with known pregestational diabetes and those who are discovered by symptoms earlier in pregnancy. Some women with previously undiscovered pregestational diabetes, however, will inevitably be detected in any screening program for GDM.

Organization of This Report

Chapter 2 of this SER documents our methods for searching and synthesizing the literature and producing this report; in these efforts, we were guided by an analytic framework and six key questions agreed to by the USPSTF. Chapter 3 presents results of our literature search and synthesis. We offer a further discussion of these results and recommendations for future research in Chapter 4. Figures and tables in the text can be found at the end of chapters where they are first called out. Appendix A contains acknowledgments to our peer reviewers, USPSTF liaisons and RTI-UNC EPC staff; Appendix B provides the detailed evidence tables for selected reviewed articles.

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