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Gestational Diabetes Mellitus (GDM)


General Information


  • GDM is diabetes diagnosed in second or third trimester of pregnancy that is clearly not overt diabetes4
  • women with diabetes in first trimester would be classified as having preexisting pregestational diabetes (type 2 diabetes or, very rarely, type 1 diabetes)4

Also called

  • gestational onset diabetes mellitus (GODM)
  • impaired glucose tolerance during pregnancy
  • gestational carbohydrate intolerance


  • types of GDM
    • insulin resistant (most women with GDM) - usually combination of
    • autoimmune beta-cell dysfunction subtype
    • monogenic forms of diabetes (such as mitochondrial diabetes with deafness [MIDDM], maturity-onset diabetes of the young [MODY])
      • 2%-5% of GDM cases, commonly misclassified as type 1 or 2 diabetes
      • young age of onset
        • 10-45 years old for MODY
        • 8-70 years old for MIDDM, mean age 35 years
      • mild hyperglycemia initially - may be first identified in routine pregnancy glucose screening
      • often no evidence of chronic insulin resistance
      • diagnosis requires genotyping
      • Reference - 23037711Swiss Med Wkly 2012 Oct 4;142:w13690OpenInNewfull-textOpenInNew
  • White Classification (types of diabetes complicating pregnancy) (rarely used to follow patients)
    • A - gestational diabetes, onset in pregnancy
      • A1 - diet controlled
      • A2 - insulin requiring
    • B - onset > 20 years old, duration < 10 years, no vascular disease
    • C - onset age 10-19 years, duration 10-19 years, no vascular disease
    • D - onset < 10 years old, duration > 20 years, some vascular disease (retina, legs)
    • E - pelvic arteriosclerosis by x-ray
    • F - vascular nephritis (renal disease)
    • R - proliferative retinopathy
    • Reference - 619663Am J Obstet Gynecol 1978 Jan 15;130(2):228OpenInNew


General references used

  1. American College of Obstetricians and Gynecologists Committee on Practice Bulletins—Obstetrics. Practice Bulletin No. 190: Gestational Diabetes Mellitus. Obstet Gynecol. 2018 Feb;131(2):e49-e64OpenInNew
  2. American Diabetes Association (ADA). 14. Management of Diabetes in Pregnancy. Diabetes Care. 2019 Jan;42(Suppl 1):S165-S172OpenInNewfull-textOpenInNew
  3. Landon MB, Gabbe SG. Gestational diabetes mellitus. Obstet Gynecol. 2011 Dec;118(6):1379-93OpenInNew
  4. American Diabetes Association.(ADA). 2. Classification and Diagnosis of Diabetes. Diabetes Care. 2019 Jan;42(Suppl 1):S13-S28OpenInNewfull-textOpenInNew
  5. Kitzmiller JL, Block JM, Brown FM, et al. Managing preexisting diabetes for pregnancy: summary of evidence and consensus recommendations for care. Diabetes Care. 2008 May;31(5):1060-79OpenInNewfull-textOpenInNew
  6. Diabetes Canada Clinical Practice Guidelines Expert Committee., Feig DS, Berger H, Donovan L, Godbout A, Kader T, Keely E, Sanghera R. Diabetes and Pregnancy. Can J Diabetes. 2018 Apr;42 Suppl 1:S255-S282OpenInNew

Recommendation grading systems used

  • United States Preventive Services Task Force (USPSTF) grading system for recommendations
    • Grade A - USPSTF recommends the service with high certainty of substantial net benefit
    • Grade B - USPSTF recommends the service with high certainty of moderate net benefit or moderate certainty of moderate-to-substantial net benefit
    • Grade C - clinicians may provide the service to select patients depending on individual circumstances, however, only small benefit is likely for most individuals without signs or symptoms
    • Grade D - USPSTF recommends against providing the service with moderate-to-high certainty of no net benefit or harms outweighing benefits
    • Grade I - insufficient evidence to assess balance of benefits and harms
    • Reference - USPSTF recommendation statement on screening for gestational diabetes mellitus (mnh24424622pmdc24424622pAnn Intern Med 2014 Mar 18;160(6):OpenInNew)
  • American Diabetes Association (ADA) evidence grading system for clinical practice recommendations
    • Grade A
      • clear evidence from well-conducted, generalizable, randomized controlled trials (RCTs) that are adequately powered, including evidence from well-conducted multicenter trial or meta-analysis that incorporated quality ratings in analysis
      • compelling nonexperimental evidence, specifically, "all or none" rule developed by Center for Evidence Based Medicine at Oxford
      • supportive evidence from well-conducted RCTs that are adequately powered, including evidence from well-conducted trial at ≥ 1 institution or meta-analysis that incorporated quality ratings in analysis
    • Grade B
      • supportive evidence from well-conducted cohort studies, including evidence from well-conducted prospective cohort study or registry or meta-analysis of cohort studies
      • supportive evidence from a well-conducted case-control study
    • Grade C
      • supportive evidence from poorly controlled or uncontrolled studies
        • evidence from randomized clinical trials with ≥ 1 major or ≥ 3 minor methodologic flaws that could invalidate results
        • evidence from observational studies with high potential for bias (such as case series with comparison to historical controls)
        • evidence from case series or case reports
      • conflicting evidence with weight of evidence supporting recommendation
    • Grade E - expert consensus or clinical experience
    • Reference - ADA 2018 position statement on standards of medical care in diabetes: introduction (29222369Diabetes Care 2018 Jan;41(Suppl 1):S1OpenInNew)
  • American College of Obstetricians and Gynecologists (ACOG) grading system for recommendations
    • Level A - based on good and consistent scientific evidence
    • Level B - based on limited or inconsistent scientific evidence
    • Level C - based primarily on consensus and expert opinion
    • Reference - ACOG Practice Bulletin 190 on gestational diabetes mellitus (29370047Obstet Gynecol 2018 Feb;131(2):e49OpenInNew)
  • Canadian Diabetes Association (CDA) grading system for recommendations
    • grades of recommendations
      • Grade A - best evidence was at Level 1
      • Grade B - best evidence was at Level 2
      • Grade C - best evidence was at Level 3
      • Grade D - best evidence was at Level 4 or consensus
    • levels of evidence
      • Studies of diagnosis
        • Level 1 - meets following criteria
          • a - independent interpretation of test results (without knowledge of result of diagnostic or gold standard)
          • b - independent interpretation of diagnostic standard (without knowledge of test result)
          • c - selection of people suspected (but not known) to have the disorder
          • d - reproducible description of both test and diagnostic standard
          • e - at least 50 patients with and 50 patients without the disorder
        • Level 2 - meets 4 of Level 1 criteria
        • Level 3 - meets 3 of Level 1 criteria
        • Level 4 - meets 1 or 2 of Level 1 criteria
      • Studies of treatment and prevention
        • Level 1A - meets either of following criteria
          • systematic overview or meta-analysis of high-quality RCTs
            • a - comprehensive search for evidence
            • b - authors avoided bias selecting articles for inclusion
            • c - authors assessed each article for validity
            • d - reports clear conclusions supported by the data and appropriate analyses
          • appropriately designed RCT with adequate power to answer the question posed by investigators
            • a - patients randomly allocated to treatment groups
            • follow up at least 80% complete
            • patients and investigators blinded to the treatment
            • patients analyzed in assigned treatment groups
            • sample size large enough to detect outcome of interest
        • Level 1B - non-randomized clinical trial or cohort study with indisputable results
        • Level 2 - RCT or systematic overview does not meet Level 1 criteria
        • Level 3 - non-randomized clinical trial or cohort study; systematic overview or meta-analysis of level 3 studies
        • Level 4 - other
      • Studies of prognosis
        • Level 1 - meets following criteria
          • a - inception cohort of patients with the condition of interest, but free of the outcome of interest
          • b - reproducible inclusion/exclusion criteria
          • c - follow up of at least 80% of subjects
          • d - statistical adjustment for extraneous prognostic factors (confounders)
          • e - reproducible description of outcome measures
        • Level 2 - meets criterion (a) above, plus 3 of the other 4 criteria
        • Level 3 - meets criterion (a) above, plus 2 of the other criteria
        • Level 4 - meets criterion (a) above, plus 1 of the other criteria
    • Reference - Diabetes Canada clinical practice guideline on diabetes and pregnancy (Can J Diabetes 2018 Apr;42 Suppl 1;S255OpenInNew), correction can be found in Can J Diabetes 2018 Jun;42(3);337OpenInNew
  • Endocrine Society uses Grading of Recommendations, Assessment, Development, and Evaluation (GRADE)
    • strength of recommendation
      • Strong recommendation - guideline panel members have high confidence that desirable effects of recommendation outweigh undesirable effects (or vice versa)
      • Weak recommendation - guideline panel members conclude with less confidence that desirable effects of recommendation probably outweigh undesirable effects, or benefits and harms are finely balanced, or appreciable uncertainty
    • quality of evidence
      • High-quality evidence - consistent evidence from well-performed randomized controlled trials, or exceptionally strong evidence from unbiased observational studies
      • Moderate-quality evidence - randomized controlled trials with important limitations (inconsistent results, methodological flaws, indirect or imprecise evidence), or unusually strong evidence from unbiased observational studies
      • Low-quality evidence - ≥ 1 critical outcome from observational studies, randomized controlled trials with serious flaws, or indirect evidence
      • Very low-quality evidence - ≥ 1 of the critical outcomes from unsystematic clinical observations or very indirect evidence

Synthesized Recommendation Grading System for DynaMed

  • DynaMed systematically monitors clinical evidence to continuously provide a synthesis of the most valid relevant evidence to support clinical decision-making (see 7-Step Evidence-Based MethodologyOpenInNew).
  • Guideline recommendations summarized in the body of a DynaMed topic are provided with the recommendation grading system used in the original guideline(s), and allow DynaMed users to quickly see where guidelines agree and where guidelines differ from each other and from the current evidence.
  • In DynaMed (DM), we synthesize the current evidence, current guidelines from leading authorities, and clinical expertise to provide recommendations to support clinical decision-making in the Overview & Recommendations section.
  • We use the Grading of Recommendations Assessment, Development and Evaluation (GRADE)OpenInNew to classify synthesized recommendations as Strong or Weak.
    • Strong recommendations are used when, based on the available evidence, clinicians (without conflicts of interest) consistently have a high degree of confidence that the desirable consequences (health benefits, decreased costs and burdens) outweigh the undesirable consequences (harms, costs, burdens).
    • Weak recommendations are used when, based on the available evidence, clinicians believe that desirable and undesirable consequences are finely balanced, or appreciable uncertainty exists about the magnitude of expected consequences (benefits and harms). Weak recommendations are used when clinicians disagree in judgments of relative benefit and harm, or have limited confidence in their judgments. Weak recommendations are also used when the range of patient values and preferences suggests that informed patients are likely to make different choices.
  • DynaMed (DM) synthesized recommendations (in the Overview & Recommendations section) are determined with a systematic methodology:
    • Recommendations are initially drafted by clinical editors (including ≥ 1 with methodological expertise and ≥ 1 with content domain expertise) aware of the best current evidence for benefits and harms, and the recommendations from guidelines.
    • Recommendations are phrased to match the strength of recommendation. Strong recommendations use "should do" phrasing, or phrasing implying an expectation to perform the recommended action for most patients. Weak recommendations use "consider" or "suggested" phrasing.
    • Recommendations are explicitly labeled as Strong recommendations or Weak recommendations when a qualified group has explicitly deliberated on making such a recommendation. Group deliberation may occur during guideline development. When group deliberation occurs through DynaMed-initiated groups:
      • Clinical questions will be formulated using the PICO (Population, Intervention, Comparison, Outcome) framework for all outcomes of interest specific to the recommendation to be developed.
      • Systematic searches will be conducted for any clinical questions where systematic searches were not already completed through DynaMed content development.
      • Evidence will be summarized for recommendation panel review including for each outcome, the relative importance of the outcome, the estimated effects comparing intervention and comparison, the sample size, and the overall quality rating for the body of evidence.
      • Recommendation panel members will be selected to include at least 3 members that together have sufficient clinical expertise for the subject(s) pertinent to the recommendation, methodological expertise for the evidence being considered, and experience with guideline development.
      • All recommendation panel members must disclose any potential conflicts of interest (professional, intellectual, and financial), and will not be included for the specific panel if a significant conflict exists for the recommendation in question.
      • Panel members will make Strong recommendations if and only if there is consistent agreement in a high confidence in the likelihood that desirable consequences outweigh undesirable consequences across the majority of expected patient values and preferences. Panel members will make Weak recommendations if there is limited confidence (or inconsistent assessment or dissenting opinions) that desirable consequences outweigh undesirable consequences across the majority of expected patient values and preferences. No recommendation will be made if there is insufficient confidence to make a recommendation.
      • All steps in this process (including evidence summaries which were shared with the panel, and identification of panel members) will be transparent and accessible in support of the recommendation.
    • Recommendations are verified by ≥ 1 editor with methodological expertise, not involved in recommendation drafting or development, with explicit confirmation that Strong recommendations are adequately supported.
    • Recommendations are published only after consensus is established with agreement in phrasing and strength of recommendation by all editors.
    • If consensus cannot be reached then the recommendation can be published with a notation of "dissenting commentary" and the dissenting commentary is included in the topic details.
    • If recommendations are questioned during peer review or post publication by a qualified individual, or reevaluation is warranted based on new information detected through systematic literature surveillance, the recommendation is subject to additional internal review.

DynaMed Editorial Process

Special acknowledgements

  • Michael S. Warren, MD, MA (Attending Hospital-Based Physician, OB/GYN, William Beaumont Hospital; Michigan, United States)
  • Dr. Warren declares no relevant financial conflicts of interest.
  • Zbys Fedorowicz, MSc, DPH, BDS, LDSRCS (Director of Bahrain Branch of the United Kingdom Cochrane Center, The Cochrane Collaboration; Awali, Bahrain)
  • Dr. Fedorowicz declares no relevant financial conflicts of interest.
  • Alan Ehrlich, MD (Executive Editor; Associate Professor of Family Medicine, University of Massachusetts Medical School; Massachusetts, United States)
  • Dr. Ehrlich declares no relevant financial conflicts of interest.
  • Editorial Team role definitions
    Topic Editors define the scope and focus of each topic by formulating a set of clinical questions and suggesting important guidelines, clinical trials, and other data to be addressed within each topic. Topic Editors also serve as consultants for the internal DynaMed Editorial Team during the writing and editing process, and review the final topic drafts prior to publication.
    Section Editors have similar responsibilities to Topic Editors but have a broader role that includes the review of multiple topics, oversight of Topic Editors, and systematic surveillance of the medical literature.
    Recommendations Editors provide explicit review of DynaMed Overview and Recommendations sections to ensure that all recommendations are sound, supported, and evidence-based. This process is described in "Synthesized Recommendation Grading."
    Deputy Editors are employees of DynaMed and oversee DynaMed internal publishing groups. Each is responsible for all content published within that group, including supervising topic development at all stages of the writing and editing process, final review of all topics prior to publication, and direction of an internal team.

How to cite

National Library of Medicine, or "Vancouver style" (International Committee of Medical Journal Editors):

  • DynaMed [Internet]. Ipswich (MA): EBSCO Information Services. 1995 - . Record No. T116237, Gestational Diabetes Mellitus (GDM); [updated 2018 Nov 30, cited place cited date here]. Available from Registration and login required.
  • KeyboardArrowRight

    Overview and Recommendations

    • Background

    • Evaluation

    • Management

  • Related Summaries

  • KeyboardArrowRight

    General Information

    • Description

    • Also called

    • Types

  • KeyboardArrowRight


    • Who is most affected

    • Incidence/Prevalence

    • Likely risk factors

    • Possible risk factors

    • Factors not associated with increased risk

    • Associated conditions

  • KeyboardArrowRight

    Etiology and Pathogenesis

    • Causes

    • Pathogenesis

  • KeyboardArrowRight

    History and Physical

    • KeyboardArrowRight


      • Chief concern (CC)

      • Past medical history (PMH)

      • Family history (FH)

      • Social history (SH)

    • KeyboardArrowRight


      • General physical

  • KeyboardArrowRight


    • Making the diagnosis

    • Differential diagnosis

    • Testing overview

    • Blood tests

    • Urine studies

    • Imaging studies

  • KeyboardArrowRight


    • Management overview

    • Delivery

    • Diet

    • Activity

    • Counseling

    • KeyboardArrowRight


      • Pharmacologic therapy considerations

      • Benefits of treatment for GDM

      • Timing of treatment

      • KeyboardArrowRight

        Insulin therapy

        • Insulin during labor

      • Oral hypoglycemic agents

      • Comparing oral agents to insulin

    • KeyboardArrowRight

      Antenatal management

      • Blood glucose monitoring strategies

      • HbA1c monitoring

      • Antenatal fetal surveillance

    • KeyboardArrowRight

      Management of diabetes-related comorbidities

      • Cardiovascular disease

      • Hypertension

    • Follow-up

  • KeyboardArrowRight

    Complications and Prognosis

    • KeyboardArrowRight


      • Maternal complications

      • KeyboardArrowRight

        Fetal complications

        • Stillbirth

        • Macrosomia and shoulder dystocia

        • Congenital malformation

        • Neonatal complications

        • Long-term complications

    • Prognosis

  • KeyboardArrowRight

    Prevention and Screening

    • KeyboardArrowRight


      • Lifestyle factors

      • Dietary interventions

      • Exercise

      • Multidisciplinary care

      • Oral hypoglycemic drugs for prevention

      • Supplements for prevention

    • KeyboardArrowRight


      • Screening recommendations

      • Evidence for screening

      • Screening tests

  • KeyboardArrowRight

    Quality Improvement

    • Physician Quality Reporting System Quality Measures

    • Choosing Wisely

  • KeyboardArrowRight

    Guidelines and Resources

    • KeyboardArrowRight


      • International guidelines

      • United States guidelines

      • Canadian guidelines

      • European guidelines

      • Mexican guidelines

      • Australian and New Zealand guidelines

    • Review articles

    • MEDLINE search

  • Patient Information

  • KeyboardArrowRight

    ICD Codes

    • ICD-10 codes

  • KeyboardArrowRight


    • General references used

    • Recommendation grading systems used

    • Synthesized Recommendation Grading System for DynaMed

    • DynaMed Editorial Process

    • Special acknowledgements

    • How to cite

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