Objective: The purpose of this document is to briefly review the existing data regarding the effect of a diagnosis of gestational diabetes mellitus (GDM), the different screening and diagnostic practices for GDM, and, finally, outline the recommended options for GDM screening in Canada.
Options: Consideration has been given to the existing screening practices for GDM including universal screening, risk factor-based screening, and the option of not screening for GDM.
Outcomes: The short- and long-term maternal-fetal outcomes in GDM were reviewed with emphasis given to examination of the data regarding the effect of diagnosis and treatment of GDM on these outcomes.
Evidence: A comprehensive search of the literature from 1990 through April 2002 using MEDLINE and the Cochrane Database and a review of randomized controlled trials (RCTs) was undertaken. Additional studies and clinical guidelines published outside this time frame but with specific clinical relevance were also reviewed. The level of evidence of the recommendations in this document has been determined using the criteria described by the Canadian Task Force on the Periodic Health Examination.
Recommendations: I. A single approach of testing for GDM cannot be recommended at the present as there is not enough evidence-based data proving the beneficial effect of a large screening program. Until a large prospective RCT shows a clear clinical benefit for screening and consequently treating GDM, recommendations will by necessity be based on consensus or expert opinion. Each of the following approaches is acceptable. a. Routine screening of women at 24-28 weeks of gestation may be recommended with the 50 g glucose challenge test (GCT), using a threshold of 7.8 mmol/L (140 mg/dL), except in those women who fulfill the criteria for low risk, which includes the following: * maternal age < 25 * Caucasian or member of other ethnic group with low prevalence of diabetes * pregnant body mass index (BMI) </= 27 * no previous history of GDM or glucose intolerance * no family history of diabetes in first-degree relative * no history of GDM-associated adverse pregnancy outcomes. The diagnostic test can be the 100 g oral glucose tolerance test (OGTT), as recommended by ACOG, or the 75 g OGTT, according to the American Diabetes Association (ADA) criteria. Use of the World Health Organization (WHO) criteria will approximately double the number of women diagnosed with GDM without an apparent clinical benefit. (III-C) b. A small but significant number of Canadian obstetricians and centres have a policy of non-screening for GDM. Until evidence is available from large RCTs that show a clear benefit from screening for glucose intolerance in pregnancy, the option of not screening for GDM is considered acceptable. Conversely, there are no compelling data to stop screening when it is practiced. (III-C) c. The clinician should consider the recommendation of the Fourth International Workshop-Conference that women considered at high risk for GDM should undergo a diagnostic test as early in pregnancy as possible and that testing should be repeated at 24-28 weeks if initial results are negative. (III-C) d. If GDM is diagnosed, glucose tolerance should be re-assessed with a 75 g OGTT 6-12 weeks postpartum in order to identify women with persistent glucose intolerance. (III-C)2. A large RCT is needed to quantify the advantages and dis-advantages of routine screening for GDM. Furthermore, the need for universally accepted, outcome-based diagnostic criteria for GDM is emphasized. (III-C) VALIDATION: This guideline was reviewed by the SOGC Maternal-Fetal Medicine Committee.
Sponsor: The Society of Obstetricians and Gynaecologists of Canada.