The summaries of the evidence briefly present evidence of effectiveness for preventive health services used in primary care clinical settings, including screening tests, counseling, and chemoprevention. They summarize the more detailed Systematic Evidence Reviews, which are used by the U.S. Preventive Services Task Force (USPSTF) to make recommendations.
Contents
Abstract
Epidemiology
Materials and Methods
Results
Discussion
Acknowledgments
References
Notes
Abstract
Objective: To systematically review the evidence for screening for gestational diabetes mellitus (GDM).
Methods: We established eligibility criteria for relevant studies. We systematically searched MEDLINE® and the Cochrane Collaboration Library for studies meeting eligibility criteria; we supplemented this search with further studies identified from reference lists of reviews. Two reviewers examined each article for eligibility. A single reviewer abstracted relevant data from the included articles; a second reviewer checked the abstractions. We graded the quality of the articles according to criteria developed by the U.S. Preventive Services Task Force (USPSTF).
Results: No well-conducted randomized controlled trial (RCT) provides direct evidence for the health benefits of screening for GDM. The evidence is unclear about the optimal screening and reference diagnostic test for GDM. The impact of hyperglycemia on adverse maternal and neonatal health outcomes is probably continuous. Although insulin therapy decreases the incidence of fetal macrosomia for those women with more severe degrees of hyperglycemia, the magnitude of any effect on maternal and neonatal health outcomes is not clear. The evidence is insufficient to determine the magnitude of health benefit for any treatment among the large number of women with GDM at milder degrees of hyperglycemia. We found limited evidence about the potential adverse effects of screening for GDM.
Conclusion: Because of the lack of high quality evidence concerning critical issues, we are unable to determine the extent to which screening has an important impact on maternal and neonatal health outcomes. An RCT of screening is necessary to answer the many remaining questions.
Epidemiology
GDM is defined as glucose intolerance with the onset or first detection during pregnancy.1,2 About 135,000 cases of GDM are diagnosed annually in the United States.2 Important risk factors include higher maternal age, family history of diabetes, and increased pregravid body mass index (BMI).3 The prevalence of GDM in low-risk populations ranges from 1.4 to 2.8 percent;4,5 in high-risk populations, prevalence ranges from 3.3 to 6.1 percent.4
Markedly elevated maternal glucose levels most often occur in women with pregestational diabetes. Pregnant women with pregestational diabetes are at higher risk for multiple complications affecting both the mother and the fetus than those women without diabetes. Current therapy improves outcomes for both mother and neonate.6
The additional risk for adverse health outcomes attributable to the milder degrees of maternal hyperglycemia associated with GDM and the magnitude of the benefit from treating that risk are less certain. No well-designed and conducted RCT of screening for GDM has been completed, and thus the evidence for screening is indirect.
National groups disagree about whether to recommend screening for GDM.2,7-11 Despite no strong recommendations in favor of universal screening from the American College of Obstetricians and Gynecologists (ACOG), 94 percent of Fellows in office-based practices reported performing universal screening for GDM in 1996.12 Fellows performed this screening even though ACOG acknowledged the weakness in the evidence in both 199413 and 2000.2
With continued controversy around the advisability of GDM screening, the RTI-University of North Carolina Evidence-based Practice Center (RTI-UNC EPC) conducted a systematic evidence review to assist the USPSTF in reconsidering its 1996 review, which found insufficient evidence to recommend screening. We restricted this review to screening for GDM after 24 weeks' gestation, thus excluding both women with known pregestational diabetes and those who are discovered by symptoms earlier in pregnancy.
