This is the current release of the guideline.

This guideline updates a previous version: U.S. Preventive Services Task Force (USPSTF). Screening for gestational diabetes mellitus: recommendations and rationale. Obstet Gynecol 2003 Feb;101(2):393-5.

Gestational diabetes mellitus (GDM)

Prevention
Screening

Endocrinology
Family Practice
Internal Medicine
Obstetrics and Gynecology

Advanced Practice Nurses
Allied Health Personnel
Health Care Providers
Nurses
Physician Assistants
Physicians

• To summarize the current U.S. Preventive Services Task Force (USPSTF) recommendations and supporting scientific evidence on screening for gestational diabetes
• To update the 2003 USPSTF recommendations on screening for gestational diabetes

Pregnant women who have not previously been diagnosed with diabetes

Routine screening for gestational diabetes mellitus (GDM) using a glucose challenge test (GCT) followed by an oral glucose tolerance test (OGTT) for women who screen positive on the glucose challenge test

Key Question 1: Does screening for gestational diabetes mellitus (GDM) lead to a reduction in perinatal morbidity and mortality for mother and/or infant? A) after 24 weeks gestation? B) during the first trimester and up to 24 weeks gestation?

Key Question 2: What are the sensitivities, specificities, reliabilities, and yields of current screening tests for GDM: A) after 24 weeks gestation? B) during the first trimester and up to 24 weeks gestation?

Key Question 3: Does treatment for GDM lead to reduction in perinatal morbidity and mortality for mother and/or infant? A) after 24 weeks gestation? B) during the first trimester and up to 24 weeks gestation?

Key Question 4: What are the adverse effects associated with screening for GDM?

Key Question 5: What are the adverse effects associated with treatment of GDM?

Hand-searches of Published Literature (Primary Sources)
Hand-searches of Published Literature (Secondary Sources)
Searches of Electronic Databases

Note from the National Guideline Clearinghouse (NGC): A systematic evidence review was prepared by the Oregon Evidence-based Practice Center (EPC) for use by the U.S. Preventive Services Task Force (USPSTF) (see the "Availability of Companion Documents" field).

Literature Search Strategy

EPC staff conducted six database searches (see Appendix A, Table 2 in the Evidence Synthesis [see "Availability of Companion Documents" field) of Medline, Cochrane Central Registry of Controlled Trials, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effectiveness, Health Technology Assessment, and the National Institute for Health and Clinical Excellence from 2000 to September 2006. The search regarding early screening searched 1966 to 1999 as this was not systematically reviewed for the 2003 report. Searches were extensively supplemented with the previous 2003 USPSTF review, outside source material from experts in the field, and from examining the bibliographies of other relevant systematic reviews.

Inclusion and Exclusion

While EPC staff conducted five searches to cover the separate focus of each KQ, they dual-reviewed all abstracts for potential inclusion for any of the KQs, utilizing the inclusion/exclusion criteria described in Appendix A, Table 3 of the Evidence Synthesis (see the "Availability of Companion Documents" field). For KQ1 and 3, they limited study design to randomized controlled trials (RCT) and controlled clinical trials (CCT) and accepted prospective studies if no RCTs or CCTs were available. For KQ 2, 4, and 5 they accepted RCTs, CCTs, and good quality observational studies.

Key Question 1: No randomized controlled trials (RCTs) comparing screening with no screening were located.

Key Question 2: No articles were found that reported sensitivity, specificity, and yield rates in a U.S. population using one of the three acceptable screening methods compared to an acceptable reference standard of the specified health outcomes.

Key Question 3: Seven studies reported in eight publications are included for part A (>24 weeks gestation) of which two are treatment versus no treatment. The remaining five studies are treatment comparisons. One prospective study evaluating early screening versus late screening and neonatal and maternal outcomes is included for part B (<24 weeks gestation).

Key Question 4: Three trials reporting on the harms of screening were included.

Key Question 5: Seven articles were found to address the harms of treatment.

Expert Consensus

Not applicable

Systematic Review with Evidence Tables

Note from the National Guideline Clearinghouse (NGC): A systematic evidence review was prepared by the Oregon Evidence-based Practice Center (EPC) for use by the U.S. Preventive Services Task Force (USPSTF) (see the "Availability of Companion Documents" field).

Article Review and Data Abstraction

Two investigators applied the inclusion/exclusion criteria to each article and marked articles for exclusion as soon as any one exclusion criteria was met. They then rated the quality of all articles meeting inclusion criteria, using the USPSTF's study-design specific criteria (Appendix B in the Evidence Synthesis [see the "Availability of Companion Documents" field), which resulted in additional excluded articles for quality reasons. Listings of excluded articles along with the reason for exclusion are in Appendix D Table 1 in the Evidence Synthesis (see the "Availability of Companion Documents" field).

There are 13 studies included in this review: seven from the 2003 USPSTF review and six located from searches or outside sources. One primary reviewer abstracted relevant information such as study setting, population, screening method, and outcomes into standardized evidence tables for each included article (Appendix C in the Evidence Synthesis [see the "Availability of Companion Documents" field]). A second reviewer checked the abstraction process for accuracy.

Literature Synthesis

EPC staff members were unable to conduct quantitative synthesis for any key question due to the heterogeneity of the screening methods and interventions. Instead, they qualitatively summarized their findings in the results text and summary tables. For Key Question 3, they stratified the evidence by those trials comparing treatment versus no treatment and trials comparing treatments.

Balance Sheets
Expert Consensus

The U.S. Preventive Services Task Force (USPSTF) systematically reviews the evidence concerning both the benefits and harms of widespread implementation of a preventive service. It then assesses the certainty of the evidence and the magnitude of the benefits and harms. On the basis of this assessment, the USPSTF assigns a letter grade to each preventive service signifying its recommendation about provision of the service (see Table below). An important, but often challenging, step is determining the balance between benefits and harms to estimate "net benefit" (that is, benefits minus harms).

Table 1. U.S. Preventive Services Task Force Recommendation Grid*

*A, B, C, D, and I (Insufficient) represent the letter grades of recommendation or statement of insufficient evidence assigned by the U.S. Preventive Services Task Force after assessing certainty and magnitude of net benefit of the service (see the "Rating Scheme for the Strength of the Recommendations" field.

The overarching question that the Task Force seeks to answer for every preventive service is whether evidence suggests that provision of the service would improve health outcomes if implemented in a general primary care population. For screening topics, this standard could be met by a large randomized, controlled trial (RCT) in a representative asymptomatic population with follow-up of all members of both the group "invited for screening" and the group "not invited for screening."

Direct RCT evidence about screening is often unavailable, so the Task Force considers indirect evidence. To guide its selection of indirect evidence, the Task Force constructs a "chain of evidence" within an analytic framework. For each key question, the body of pertinent literature is critically appraised, focusing on the following 6 questions:

1. Do the studies have the appropriate research design to answer the key question(s)?
2. To what extent are the existing studies of high quality? (i.e., what is the internal validity?)
3. To what extent are the results of the studies generalizable to the general U.S. primary care population and situation? (i.e., what is the external validity?)
4. How many studies have been conducted that address the key question(s)? How large are the studies? (i.e., what is the precision of the evidence?)
5. How consistent are the results of the studies?
6. Are there additional factors that assist us in drawing conclusions (e.g., presence or absence of dose-response effects, fit within a biologic model)?

The next step in the Task Force process is to use the evidence from the key questions to assess whether there would be net benefit if the service were implemented. In 2001, the USPSTF published an article that documented its systematic processes of evidence evaluation and recommendation development. At that time, the Task Force's overall assessment of evidence was described as good, fair, or poor. The Task Force realized that this rating seemed to apply only to how well studies were conducted and did not fully capture all of the issues that go into an overall assessment of the evidence about net benefit. To avoid confusion, the USPSTF has changed its terminology. Whereas individual study quality will continue to be characterized as good, fair, or poor, the term certainty will now be used to describe the Task Force's assessment of the overall body of evidence about net benefit of a preventive service and the likelihood that the assessment is correct. Certainty will be determined by considering all 6 questions listed above; the judgment about certainty will be described as high, moderate, or low.

In making its assessment of certainty about net benefit, the evaluation of the evidence from each key question plays a primary role. It is important to note that the Task Force makes recommendations for real-world medical practice in the United States and must determine to what extent the evidence for each key question—even evidence from screening RCTs or treatment RCTs—can be applied to the general primary care population. Frequently, studies are conducted in highly selected populations under special conditions. The Task Force must consider differences between the general primary care population and the populations studied in RCTs and make judgments about the likelihood of observing the same effect in actual practice.

It is also important to note that 1 of the key questions in the analytic framework refers to the potential harms of the preventive service. The Task Force considers the evidence about the benefits and harms of preventive services separately and equally. Data about harms are often obtained from observational studies because harms observed in RCTs may not be representative of those found in usual practice and because some harms are not completely measured and reported in RCTs.

Putting the body of evidence for all key questions together as a chain, the Task Force assesses the certainty of net benefit of a preventive service by asking the 6 major questions listed above. The Task Force would rate a body of convincing evidence about the benefits of a service that, for example, derives from several RCTs of screening in which the estimate of benefits can be generalized to the general primary care population as "high" certainty (see the "Rating Scheme for the Strength of Recommendations" field). The Task Force would rate a body of evidence that was not clearly applicable to general practice or has other defects in quality, research design, or consistency of studies as "moderate" certainty. Certainty is "low" when, for example, there are gaps in the evidence linking parts of the analytic framework, when evidence to determine the harms of treatment is unavailable, or when evidence about the benefits of treatment is insufficient. Table 4 in the methodology document listed below (see "Availability of Companion Documents" field) summarizes the current terminology used by the Task Force to describe the critical assessment of evidence at all 3 levels: individual studies, key questions, and overall certainty of net benefit of the preventive service.

Sawaya GF et al., Update on the methods of the U.S. Preventive Services Task Force: estimating certainty and magnitude of net benefit. Ann Intern Med. 2007;147:871-875 [5 references].

What the United States Preventive Services Task Force (USPSTF) Grades Mean and Suggestions for Practice

USPSTF Levels of Certainty Regarding Net Benefit

Definition: The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.

A formal cost analysis was not performed and published cost analyses were not reviewed.

Comparison with Guidelines from Other Groups
External Peer Review
Internal Peer Review

Peer Review. Before the U.S. Preventive Services Task Force (USPSTF) makes its final determinations about recommendations on a given preventive service, the Evidence-based Practice Center and the Agency for Healthcare Research and Quality send a draft systematic evidence review to 4 to 6 external experts and to federal agencies. They ask the experts to examine the review critically for accuracy and completeness and to respond to a series of specific questions about the document. After assembling these external review comments and documenting the proposed response to key comments, the topic team presents this information to the Task Force in memo form. In this way, the Task Force can consider these external comments and a final version of the systematic review before it votes on its recommendations about the service. Draft recommendations are then circulated for comment from reviewers representing professional societies, voluntary organizations and Federal agencies. These comments are discussed before the whole U.S. Preventive Services Task Force before final recommendations are confirmed.

Recommendations of Others. Recommendations regarding screening for gestational diabetes were discussed from the following groups: American College of Obstetricians and Gynecologists (ACOG), American Diabetes Association (ADA), and the American Academy of Family Physicians (AAFP).

The US Preventive Services Task Force (USPSTF) grades its recommendations (A, B, C, D, or I) and identifies the Levels of Certainty regarding Net Benefit (High, Moderate, and Low). The definitions of these grades can be found at the end of the "Major Recommendations" field.

Summary of Recommendations and Evidence

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for gestational diabetes mellitus (GDM), either before or after 24 weeks gestation. This is an I statement.

Clinical Considerations

Patient Population Under Consideration

This recommendation concerns pregnant women who have not previously been diagnosed with diabetes.

Suggestions for Practice Regarding the I Statement

Until there is better evidence, clinicians should discuss screening for GDM with their patients and make case-by-case decisions. Discussions should include information about the uncertainty of benefits and harms as well as the frequency of positive screening test results.

Assessment of Risk

Women who are obese, older than 25 years of age, have a family history of diabetes, have a history of previous GDM, or are of certain ethnic groups (Hispanic, American Indian, Asian, or African-American) are at increased risk of developing GDM.

Screening Tests

In the United States, the most common screening test is an initial 50-gram 1-hour glucose challenge test (GCT). If the result of the GCT is abnormal, variably defined as either greater than 130 mg/dL or 140 mg/dL, the patient undergoes a 100-gram 3-hour oral glucose tolerance test (OGTT). Two or more abnormal values on the OGTT are considered a diagnosis of GDM.

Time of Screening

Most screening is conducted between 24 and 28 weeks gestation. There is little evidence about the value of earlier screening.

Treatment

Treatment usually includes recommendations for physical activity and dietary modification. In addition, treatment sometimes includes medication (either insulin or oral hypoglycemic agents), support from diabetes educators and nutritionists, and increased surveillance in prenatal care. The extent to which these interventions improve health outcomes is uncertain.

Other Approaches to Prevention

Nearly all pregnant women should be encouraged to achieve moderate weight gain based on their pre-pregnancy body mass index (BMI) and to participate in physical activity.

Definitions:

What the United States Preventive Services Task Force (USPSTF) Grades Mean and Suggestions for Practice

USPSTF Levels of Certainty Regarding Net Benefit

Definition: The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.

None provided

The type of supporting evidence is not specifically stated for each recommendation.

Benefits of Detection and Early Treatment

Screening Before 24 Weeks Gestation

The evidence is poor to determine whether there are benefits to screening women at this time in pregnancy.

Screening After 24 Weeks Gestation

Although screening and early treatment of gestational diabetes mellitus (GDM) reduces macrosomia, and although 1 trial suggests the possibility of other health benefits, the overall evidence is poor to determine whether maternal or fetal complications are reduced by screening.

Harms of Detection and Early Treatment

There is fair evidence that short-term anxiety occurs in some women with positive screening results; longer term psychological or other harms have not been documented. The majority of positive screening test results are probably false positives. Consequently, it is likely that many women and medical practices are being inconvenienced unnecessarily by screening.

• The U.S. Preventive Services Task Force (USPSTF) makes recommendations about preventive care services for patients without recognized signs or symptoms of the target condition.
• Recommendations are based on a systematic review of the evidence of the benefits and harms and an assessment of the net benefit of the service.
• The USPSTF recognizes that clinical or policy decisions involve more considerations than this body of evidence alone. Clinicians and policy-makers should understand the evidence but individualize decision making to the specific patient or situation.

Staying Healthy

Effectiveness
Patient-centeredness

Not applicable: The guideline was not adapted from another source.

1996 (revised 2008 May)

United States Preventive Services Task Force - Independent Expert Panel

The U.S. Preventive Services Task Force (USPSTF) is a Federally-appointed panel of independent experts. Conclusions of the USPSTF do not necessarily reflect policy of the U.S. Department of Health and Human Services (DHHS) or DHHS agencies.

United States Government

U.S. Preventive Services Task Force (USPSTF)

The U.S. Preventive Services Task Force has an explicit policy concerning conflict of interest. All members disclose at each meeting if they have a significant financial, professional/business, or intellectual conflict for each topic being discussed. Task Force members with conflicts may be recused from discussing or voting on recommendations about the topic in question.

This is the current release of the guideline.

This guideline updates a previous version: U.S. Preventive Services Task Force (USPSTF). Screening for gestational diabetes mellitus: recommendations and rationale. Obstet Gynecol 2003 Feb;101(2):393-5.

This summary was completed by ECRI on June 30, 1998. The information was verified by the guideline developer on December 1, 1998. This summary was updated by ECRI on January 30, 2003. This NGC summary was updated by ECRI Institute on May 6, 2008. The updated information was verified by the guideline developer on May 21, 2008.