Maternity Care Calendar and Guidelines: screening for gestational diabetes

Literature Search:

Medline was searched using the MeSH exp Diabetes, gestational or gestational diabetes.mp (keyword and MeSH) AND mass screening.mp or exp Mass Screening (keyword and MeSH) limited to English and human from 1998-2005. This search yielded 97 articles. Clinical practice guidelines, review articles and randomized controlled trials were selected. EBM reviews including the Cochrane Database of Systematic Reviews (CDSR), ACP Journal Club, Database of Abstracts and Reviews of Effectiveness (DARE) and Cochrane Central Register of Controlled Trials (CCTR) were searched using the keywords gestational diabetes and pregnancy. The Canadian Task Force on Preventive Health Care, the US Preventive Services Task Force, the CMA Infobase of Clinical Practice Guidelines and the US National Guideline Clearinghouse were also reviewed for guidelines gestational diabetes screening. Guidelines from the Institute for Clinical Systems Improvement and the National Institute for Clinical Excellence were reviewed. The websites for national associations of obstetricians and gynecologists and family physicians (ACOG, SOGC, RCOG, AAFP, CFP) were also checked for clinical practice guidelines. Recent position statements by the American Diabetes Association, the Fourth International Workshop-Conference on Gestational, Diabetes Mellitus, and the Canadian Diabetes Association Guidelines were also examined, as were guidelines from the ADIPS (Australian Diabetes in Pregnancy Society).

Summary of Evidence:

Gestational diabetes (GDM) has been defined as carbohydrate intolerance that begins or is first recognized in pregnancy. [1-3] The prevalence of GDM is often estimated at between 2-5%. [1, 2]Women with gestational diabetes more often develop hypertensive disorders, although it is unclear whether the relationship is causal. Women with GDM are also more likely undergo Caesarian section and to develop diabetes later in life.[2-5] Infants born to women with GDM are at increased risk of macrosomia, hyperbilirubinemia, operative delivery, shoulder dystocia and birth trauma. [2, 3, 5]

The screening and diagnosis of GDM remains controversial. There is as of yet no Level 1 evidence consisting of randomized prospective double-blind controlled trials to show the relationship between the diagnosis and management of GDM and its influence on perinatal outcomes. Because of this lack of sound scientific data, there has been world-wide debate on the issues of universal screening vs. selective screening, as well as the conduct and interpretation of the diagnostic oral glucose tolerance test (OGGT). However, as pointed out by Coustran, "the fact that the evidence does not support screening is not the same as a statement that the evidence supports not screening".[6]
Despite the lack of clear evidence to support screening, in one American study, 94% of the practitioners surveyed reported universal screening. [7]

Who to screen
Since 1998, the trend has shifted from universal screening to selective screening, acknowledging that for women at low risk of GDM, screening may not be cost-effective. To be considered low risk, a woman must have all the following clinical characteristics: age <25yrs, belonging to a low-risk ethnic group, no diabetes in first-degree relatives, weight normal before pregnancy, no history of abnormal glucose metabolism, and no history of poor obstetric outcome. Both the Fourth International Workshop-Conference on Gestational Diabetes Mellitus and the most recent position statement by the American Diabetes Association have adopted these recommendations.[1, 8] A recent study found that these six selective screening criteria would miss few women (~3%) but that the majority of the pregnant population do not have all these characteristics (~90%) and would therefore have to be screened. The American College of Obstetricians and Gynecologists (ACOG) has adopted a similar recommendation for selective screening or universal screening based on consensus and expert opinion. [9] However, controversy still remains; both the Canadian Task Force on Preventive Health Care and the US Preventive Services Task Force found insufficient evidence for or against screening for GDM using a rigorous systematic review of the literature.(see discussion below) The SOGC recommendations accept both options -to screen or not screen as there is no definitive evidence to recommend one approach over the other.[3] ADIPS guidelines recommend universal screening except in areas of low incidence and in cases where resources are limited, where selective screening based on risk factors may be appropriate.[10]

How to screen
The protocol most used in North America is a two step scheme: a screening test consisting of a one hour 50 g glucose challenge test at 24-28 weeks of pregnancy, followed by a diagnostic three hour 100 g in case of a positive screening test. This is currently advocated as an option by the Fourth International Workshop-Conference on Gestational Diabetes Mellitus, the American Diabetes Association, and the SOGC.[3, 4, 8]

The second strategy (mostly used in Europe) is a one step procedure using a two hour 75g tolerance test as proposed by the World Health Organization in 1985. [11] This procedure has the benefit of ease and acceptability for pregnant woman, comparability to the postpartum 75g, 2 hour OGTT, and if adopted in North America, would simplify worldwide comparison of data.[6, 12] The Fourth International Workshop-Conference on Gestational Diabetes Mellitus has given the one step procedure equal status to that of the 100 g, 3 hour test, though it admitted that cut-off values were (out of necessity) arbitrary.[8]

Neither of these criteria are based on the potential to detect pregnancies at risk for adverse perinatal outcome as a result of maternal hyperglycemia, and thus it remains difficult to come to consensus on the gold standard to diagnose GDM.[12]

A recent prospective population based study advocated the use of a fasting plasma glucose concentration as an easier screening procedure than the 1 hour 50g GCT, yielding better sensitivity and acceptable specificity. However, 30% of women would have to be referred for the OGGT with the FPG screen, as opposed to 14% of those screened with the 50g GCT.[13] Although the authors feel this is compensated by the avoidance of the challenge test in all patients, wide acceptance of this procedure has not been reached.

Recommendations of Others:

Canadian Task Force on Preventive Health Care (CTFPHC):

The most recent review by the CTFPHE was first published in 1992.[14] It is available on the website: http://www.ctfphc.org/. They make the following recommendations:

There is poor evidence to include or exclude (in the PHE of pregnant women) screening using the 1-hour 50 g OGCT [C, II-1, II-2, III] or fasting and random blood glucose levels [C, III].
There is poor evidence to include or exclude (in the PHE of pregnant women) searching for risk factors for GDM (history of miscarriage, fetal death, premature infant or infant with macrosomia or congenital malformation; family history; obesity; ? 40 years of age; polyhydramnios; pre-eclampsia; excessive weight gain and glycosuria) at first visit and testing for glycosuria at each visit, with follow-up of positive results with fasting, postprandial and oral glucose tolerance tests. [C, III]

U.S. Preventive Services Task Force (USPSTF):

The US Preventive services task Force just released a review on screening for gestational diabetes. [5] It can be found at: http://www.ahcpr.gov/clinic/3rduspstf/gdm/gdmsum.pdf

The U.S. Preventive Services Task Force (USPSTF) concludes that the evidence is insufficient to recommend for or against routine screening for gestational diabetes. I recommendation.
Rationale: The USPSTF found fair to good evidence that screening combined with diet and insulin therapy can reduce the rate of fetal macrosomia in women with gestational diabetes mellitus (GDM). The USPSTF found insufficient evidence, however, that screening for GDM substantially reduces important adverse health outcomes for mothers or their infants (for example, cesarean delivery, birth injury, or neonatal morbidity or mortality). Screening produces frequent false-positive results, and the diagnosis of GDM may be associated with other harms, such as negatively affecting a woman's perception of her health, but data are limited. Therefore, the USPSTF could not determine the balance of benefits and harms of screening for GDM.

American College of Obstetricians and Gynecologists (ACOG):

An ACOG Practice Bulletin, released in 2001, makes the following recommendations:[2]

"all pregnant patients should be screened for GDM, whether by history, clinical risk factors or laboratory screening test." (the optimal method of screening is controversial due to insufficient evidence)
"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."

low risk women should have all of the following characteristics:
1. age < 25
2. not Hispanic, African, Native American, South or East Asian or Pacific Island ancestry
3. body mass index <= 25
4. no history of abnormal glucose tolerance
5. no previous pregnancy with an adverse outcome usually associated with GDM
6. no first degree relative with diabetes
the screening test should consist of a 50g, 1 hour oral glucose challenge at 24-28 weeks (the test may be administered without regard to the time elapsed since the last meal)
a screening test threshold of either 130 mg/dl or 140 mg/dl is acceptable (140 is 10% less sensitive, but produces less false positives)

Society of Obstetricians and Gynaecologists of Canada (SOGC):
The SOGC recently published a detailed clinical practice guideline on screening for gestational diabetes.[3] It is available at
http://www.sogc.org/sogcnet/sogc%5Fdocs/common/guide/pdfs/ps121%5F1.pdf

They make the following recommendations:

A single approach to screening for GDM cannot be recommended at 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.
1. 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 75g 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)
2. 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 shows 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)
3. 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) In a subsequent letter to the editor to clarify their position, the authors point out that the initial testing is to diagnose pre-existing diabetes, while the testing at 24-28 weeks is to diagnose gestational diabetes. They note the high rates of false positives seen in this population with the 50g glucose challenge screening test and recommend using a diagnostic test.[15]
4. If GDM is diagnosed, glucose tolerance should be reassessed with a 75 g OGTT 6-12 weeks postpartum in order to identify women with persistent glucose intolerance.8,73 (III-C)

A large RCT is needed to quantify the advantages and disadvantages of routine screening for GDM. Furthermore, the need for universally accepted, outcome-based diagnostic criteria for GDM is emphasized. (III-C)

American Diabetes Association:

In 2003, the American Diabetes Association published a position statement[4] based on the summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus [8]and the Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. [1] They recommend the following approach:

Risk for gestational diabetes mellitus should be ascertained at the first prenatal visit

Low risk:

Not a member of an ethnic group with a high prevalence of GDM (Hispanic, African, Native American, South or East Asian, Pacific Islands, or Indigenous Australian ancestry)
Age <25 years
Weight normal before pregnancy
No history of abnormal glucose tolerance
No history of poor obstetric outcome
No known diabetes in first-degree relatives

Average risk:

One-step protocol: 75 g, 2-hour oral glucose tolerance test on all women:

Fasting: < 5.3 mmol/L 95 mg/dl
1 hour: < 10.0 mmol/L 180 mg/dl
2 hour: < 8.6 mmol/L 155 mg/dl

(note -these criteria are, of necessity, arbitrary, as there are no data relating test results to perinatal outcome)
The one-step approach may be cost-effective in high-risk patients or populations

Two-step protocol: 50 g, 1 hour plasma glucose on all women without regard to time of day or time of last meal: In fed state, threshold is > 7.8mmol/L. (sensitivity of approximately 80% at this threshold) Women with a positive screen require a diagnostic test with 100 g, 3 hours, in fasting state:
Fasting: < 5.3 mmol/L 95 mg/dl
1 hour: < 10 mmol/L 180 mg/dl
2 hour: < 8.6 mmol/L 155 mg/dl
3 hour: < 7.8 mmol/L 140 mg/dl

(note -these criteria have been shown to designate a population at increased risk for poor outcomes)

High risk:
(marked obesity, strong family history of type 2 diabetes, personal history of GDM, glucose intolerance or glucosuria)

Perform testing as soon as feasible. If negative, repeat at 24-28 weeks.
a 50 g glucose challenge can be used in these cases.

all patients with GDM during pregnancy should be re-evaluated at 6-12 weeks postpartum.

The report from the Fourth International Workshop-Conference on GDM does not describe the methods used to develop the recommendations in detail, but it appears to be a consensus report developed by a group of experts in the field. They make the statement that "more widespread testing and identification of GDM as well as intensive management appear to be associated with a decrease in overall morbidity of infants of mothers with GDM" -but do not provide a reference. They do not discuss the lack of randomized trials showing that screening for GDM improves outcomes for mother or baby. It appears that they are beginning with the assumption that screening is appropriate and addressing the issue of how best to screen. Similarly, the Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus does not describe what methods were used to review the scientific literature. They state that clinical recognition of GDM is important because of a study by Langer et. al. showing that intensive management of GDM leads to better outcomes than conventional management.

The American Diabetes Association 2005 position statement [16] confirms these views. They note that the 75 g 2 hour OGTT is not as well validated as the 100 g 3 hour OGTT, but that both are acceptable diagnostic tests.

Canadian Diabetes Association
The Canadian Diabetes Association 2003 clinical Practice guidelines for the prevention and management of diabetes in Canada state that all pregnant women should be screened for gestational diabetes mellitus between 24-28 weeks' gestation. They recommend a 1-hour plasma glucose measurement following a 50g glucose load. If the 1hPG is > 10.3 mmol/L the diagnosis is confirmed. If the 1 hPG is 7.8-10.2, mmol/L, a 75-g oral glucose tolerance test should be conducted. [17]

Institute for Clinical Systems Improvement (ICSI):
Recent guidelines for prenatal care from the Institute for Clinical systems Improvement make the following recommendation:[18]

"although there is lack of consensus in the medical literature regarding universal screening, it is recommended at this time that all pregnant women be screened for gestational diabetes at 28 weeks gestation."

Royal College of Obstetricians and Gynaecologists (RCOG):
The RCOG website was search using the term gestational diabetes. No guideline was found.

National Institute for Clinical Excellence (NICE):
These British Guidelines state: "the evidence does not support routine screening for gestational diabetes and therefore it should not be offered. "(grade B evidence) [19]

Cochrane Collaboration:
The Cochrane Database of Systematic Reviews was searched for articles on screening for gestational diabetes. None were found.

Conclusions:

The lack of consensus makes it difficult to come up with a brief recommendation for the maternity care calendar. It is clear that the recommendation must remain in plain type, as of yet no level 1 or 2 evidence exists to support screening. The most rigorous systematic reviews (the CTFPHC and the USPSTF) state the there is no clear evidence for or against screening. However, a number of the influential organizations including the American Diabetes Association, the Fourth International Workshop-Conference on Gestational Diabetes Mellitus and the American College of Obstetricians and Gynecologists have produced consensus reports recommending a selective screening program based on clinical risk assessment. Also, studies show that the majority of obstetric practitioners do screen for gestational diabetes. The SOGC guidelines adopt a very reasonable approach to deal with this lack of evidence giving 2 options -to screen (using the 2-step approach) or not to screen. This will be reflected in our recommendation by the phrase "consider screening at 24 - 28 weeks� "

The two-step screening protocol (50 g load, followed by a diagnostic 3 hour OGTT for women with a positive screen) remains in more common use in North America. However, as mentioned above, consideration is being given to the one-step procedure by the Fourth International Workshop-Conference on Gestational Diabetes Mellitus, and is advocated by many authors on the basis of ease, acceptability, and worldwide comparability. Without evidence pointing to a clear gold standard, the new maternity care recommendation should include the one-step procedure as an alternative. Thus, the guideline would read: "consider testing at 24 - 28 weeks with either two-step (1 hour 50 g GCT, not fasting; if 7.8 mmol or above do 3 hour 100 g OGGT) OR 1 step (2 hour 75 g OGGT, fasting) procedure".

As one author explains, "the controversy will only end once a robust, randomized, double-blind trial is conducted to demonstrate whether identification and management of gestational diabetes is associated with significant improvement in neonatal or maternal outcomes." [20] Apparently a randomized clinical trial is now underway and should address some of the ongoing controversy. [21]

A new statement for screening high-risk women early in pregnancy will be added. The Fourth International Workshop-Conference on Gestational Diabetes Mellitus report state that a standard 50 g glucose challenge can be used in these cases. [8]

The new guideline on the MCC will be as follows:

test women at high risk for diabetes (50 g, GCT), if neg repeat at 24-28 weeks
plain font
location: under investigations for the first prenatal visit
consider glucose test between 24 - 28 weeks unless low risk with either two-step (1 hour 50 g GCT, not fasting- if 7.8 mmol or above do 3 hour 100 g OGTT) OR 1 step (2 hour 75 g OGGT, fasting) procedure, *
plain font
location: under "Investigations" in the mid-trimester
due to space constraints, low risk criteria will be available on the website

Reviewers:
Lisa Steinke, medical student - April 2002
Colleen Kirkham, MD, CCFP, FCFP - March 2003
Colleen Kirkham - March 2005

3/29/2005 10:03:00 PM

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