U.S. Preventive Services Task Force*Summary for Patients
U.S. Preventive Services Task Force*
20 May 2008 | Volume 148 Issue 10 | Pages 759-765
Description: Update of 2003 U.S. Preventive Services Task Force(USPSTF) recommendation about screening for gestational diabetes.
Methods: The USPSTF weighed the evidence on maternal and neonatalbenefits (reduction in preeclampsia, mortality, brachial plexusinjury, clavicular fractures, admission to the neonatal intensivecare unit for serious illnesses) and harms (physical and psychologicalharms) of screening for gestational diabetes identified fortheir 2003 recommendation and the accompanying systematic reviewof articles published since the 2003 review for screening after24 weeks' gestation. Additional searches were performed forevidence published from 1966 to 1999 on screening before 24weeks.
Recommendation: Current evidence is insufficient to assessthe balance of benefits and harms of screening for gestationaldiabetes mellitus, either before or after 24 weeks' gestation.(I statement.)
The U.S. Preventive Services Task Force (USPSTF) makes recommendationsabout preventive care services for patients without recognizedsigns or symptoms of the target condition.
It bases its recommendations on a systematic review of the evidenceof the benefits and harms and an assessment of the net benefitof the service.
The USPSTF recognizes that clinical or policy decisions involvemore considerations than this body of evidence alone. Cliniciansand policymakers should understand the evidence but individualizedecision making to the specific patient or situation.
Summary of Recommendation and Evidence
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See the Figure for a summary of the recommendation and suggestionsfor clinical practice.
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Table 1 describes the USPSTF grades, and Table 2 describes theUSPSTF classification of levels of certainty about net benefit.
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Rationale
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Pregestational diabetes refers to diabetes diagnosed beforepregnancy. Gestational diabetes refers to any degree of glucoseintolerance with onset or first recognition during pregnancy.Pregnant women with pregestational diabetes are at increasedrisk for multiple complications affecting both the mother andthe fetus. The degree to which pregnant women with gestationaldiabetes are at increased risk for maternal or fetal complicationsis less certain.
Detection
Several different methods are used to screen for gestationaldiabetes; many women with positive screening test results donot meet current diagnostic criteria for gestational diabetes.
Benefits of Detection and Early Treatment
Screening before 24 Weeks' Gestation
The evidence is poor to determine whether there are benefitsto screening women at this time in pregnancy.
Screening after 24 Weeks' Gestation
Although screening and early treatment of gestational diabetesreduce macrosomia, and although 1 trial suggests the possibilityof other health benefits, the overall evidence is poor to determinewhether maternal or fetal complications are reduced by screening.
Harms of Detection and Early Treatment
There is fair evidence that short-term anxiety occurs in somewomen with positive screening results; longer-term psychologicalor other harms have not been documented. The majority of positivescreening test results are probably false positive. Consequently,it is likely that many women and medical practices are beinginconvenienced unnecessarily by screening.
USPSTF Assessment
The USPSTF concludes that the current evidence is insufficientto assess the balance between the benefits and harms of screeningwomen for gestational diabetes either before or after 24 weeks'gestation.
Clinical Considerations
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This recommendation concerns pregnant women who have not previouslybeen diagnosed with diabetes.
Suggestions for Practice Regarding the I Statement
Until there is better evidence, clinicians should discuss screeningfor gestational diabetes with their patients and make case-by-casedecisions. Discussions should include information about theuncertainty of benefits and harms, as well as the frequencyof positive screening test results.
Assessment of Risk
Women who are obese, are older than 25 years of age, have afamily history of diabetes, have a history of previous gestationaldiabetes, or are of certain ethnic groups (Hispanic, AmericanIndian, Asian, or African-American) are at increased risk fordeveloping gestational diabetes.
Screening Tests
In the United States, the most common screening test is an initial50-g 1-hour glucose challenge test. If the result of the glucosechallenge test is abnormal, variably defined as either greaterthan 130 mg/dL or greater than 140 mg/dL, the patient undergoesa 100-g 3-hour oral glucose tolerance test. Two or more abnormalvalues on the oral glucose tolerance test are considered a diagnosisof gestational diabetes.
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 activityand dietary modification. In addition, treatment sometimes includesmedication (either insulin or oral hypoglycemic agents), supportfrom diabetes educators and nutritionists, and increased surveillancein prenatal care. The extent to which these interventions improvehealth outcomes is uncertain.
Other Approaches to Prevention
Nearly all pregnant women should be encouraged to achieve moderateweight gain based on their prepregnancy body mass index andto participate in physical activity.
Other Considerations
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Prospective studies on the health outcomes of women with variousglucose levels, adjusted for obesity, would help us better understandwhat level of glucose constitutes an important risk to motheror fetus. It is hoped that the Hyperglycemia and Adverse PregnancyOutcome study, which is now in the data analysis phase, willprovide useful information on this issue. Future studies shouldexamine glucose levels before 24 weeks' gestation as well asduring the 24- to 28-week gestational period. They should presentdata on women with specific risk factors, such as prepregnancyobesity, older- or younger-than-optimal age, and history ofprevious large-for-gestational-age births, along with data onwomen with no recognized risk factors. In addition, furtherrandomized trials comparing the health outcomes of loweringglucose with the health outcomes of not intervening, for womenwho have screening-detected gestational diabetes, would addweight to the findings of the ACHOIS (Australian CarbohydrateIntolerance Study in Pregnant Women). The Maternal-Fetal MedicineUnits network is conducting a randomized, controlled trial (RCT)now in progress and intending to complete recruitment in thenext 2 years, which should help provide this information. Inaddition to outcomes studies, more definitive data are requiredon the most appropriate screening strategies for gestationaldiabetes, including information on the best glucose load andtiming.
Discussion
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Gestational diabetes mellitus is currently defined as any degreeof glucose intolerance with onset or first recognition duringpregnancy (1). This definition does not exclude glucose intolerancethat may have antedated pregnancy. The current prevalence ofgestational diabetes in the United States ranges from 1% to9%, depending on the characteristics of the population screened(2, 3). In women with defined low-risk factors, such as whiteethnic origin, age younger than 25 years, and a body mass indexof less than 25 kg/m2, prevalence of gestational diabetes rangesfrom 1.4% to 2.8% (4–9). The prevalence in women withdefined high-risk factors, such as age older than 25 years,obesity, or a family history of diabetes, ranges from 3.3% to6.1% (7). Higher rates have been reported in certain ethnicgroups (2, 3). Variations in screening practices and in theprevalence of other risk factors make it difficult to quantifythe independent contribution of race and ethnicity to the developmentof gestational diabetes.
Scope of Review
In 2003, the USPSTF concluded that the scientific evidence wasinsufficient to support a recommendation for or against routinescreening of gestational diabetes in all pregnant women. Therewas fair to good evidence that screening, combined with therapyfor gestational diabetes, can reduce the rate of fetal macrosomia,but the USPSTF was unable to find sufficient evidence that gestationaldiabetes screening reduced adverse health outcomes for mothersor their infants (10).
With the increasing prevalence of U.S. women at high risk fortype 2 diabetes and gestational diabetes, the issue of earlyscreening is becoming increasingly important. The previous USPSTFreview did not include evidence related to gestational diabetesscreening before 24 weeks' gestation. The current review consideredall evidence from the previous review, and identified and evaluatedevidence that has become available since the prior review, onthe risks and benefits of gestational diabetes screening at24 weeks or later. In addition, the USPSTF reviewed all availableevidence pertaining to gestational diabetes screening before24 weeks.
The USPSTF reviewed the evidence for benefits of screening inthe following health outcomes: perinatal mortality; brachialplexus injury; clavicular fracture; maternal mortality; preeclampsia;and admission to neonatal intensive care units for hypoglycemia,hyperbilirubinemia, or the respiratory distress syndrome. Intermediateoutcomes, such as macrosomia and cesarean or vaginal delivery,were not systematically reviewed.
Accuracy of Screening Tests
There are studies that report the sensitivity and specificityof various gestational diabetes screening tests as predictorsfor gestational diabetes. However, the USPSTF found no studiesthat met its inclusion criteria. The evaluation of screeningtest performance in gestational diabetes is complicated by themany different accepted standards for screening tests, diagnostictests, and diagnostic criteria. Test performance can be evaluatedonly in the context of how accurately the test identifies peoplewith disease (sensitivity) and excludes those without disease(specificity). However, with gestational diabetes, the "disease"is actually many potential outcomes—and for 2 differentpeople (mother and baby). In addition, the generally acceptedprimary outcomes (for example, stillbirth, neonatal death, brachialplexus injury) are rare events that make estimates unstableexcept in a very large study. Data to support specific timingfor screening are also sparse.
Effectiveness of Early Detection or Treatment
No properly conducted RCT has examined the benefit of universalor selective screening for gestational diabetes compared withno screening. Two RCTs have studied treatment versus no treatmentof gestational diabetes in screening-detected populations: onerecent (ACHOIS [11]) and one conducted more than 4 decades ago(a study by O'Sullivan and colleagues [12]). Both of these trialsrandomly assigned participants to treatment or no treatmentof gestational diabetes on the basis of a universal screeningprogram approach. The ACHOIS reported that dietary management,glucose monitoring, and insulin treatment as needed in 1000women with mild gestational diabetes diagnosed after 24 weeks'gestation improved the composite neonatal outcome compared withno treatment (11). The composite outcome was defined as oneor more of the following: death, shoulder dystocia, bone fracture,and nerve palsy. The majority of the actual outcomes summedin this composite outcome were shoulder dystocia, an outcomenot considered by the USPSTF review as a final health outcome.Perinatal mortality, although rare, did not occur in any ofthe 490 babies born to mothers who were treated, compared with5 total stillbirths or neonatal deaths among the 510 women inthe untreated group. Women in the treatment group had a 30%lower risk for pregnancy-induced hypertension (defined as bloodpressure >140/90 mm Hg on 2 occasions more than 4 hours apart)compared with women who were not treated for gestational diabetes;the rate of pregnancy-induced hypertension was 18% in the untreatedwomen and 12% in the treated group (adjusted relative risk,0.70 [95% CI, 0.51 to 0.95]). Because glucose control was notpart of data collection and was not reported, the relative effectof glycemic control (versus weight control) on the improvementof outcomes with treatment cannot be estimated. All that canbe concluded is that treatment improved some outcomes.
The fair-quality RCT by O'Sullivan and colleagues (12) foundthat treatment in a screened population of women at high riskfor gestational diabetes (gestational age at screening unspecified)reduced the intermediate outcome of macrosomia but did not reducethe perinatal mortality rate. High risk was defined as a historyof delivery of a baby weighing more than 9 pounds, "toxemia"in 2 or more pregnancies, fetal or neonatal death, congenitalanomaly, or prematurity. Treatment was a small daily dose ofinsulin (10 units) initially, with irregular glucose monitoringof urine and blood (glucose monitoring was not available 40years ago). In contrast, the ACHOIS participants used insulinonly if other therapies failed to achieve tight glycemic controlbased on the study's glucose targets, and only 17% of the treatmentgroup required insulin.
The USPSTF identified no RCTs for screening and treatment before24 weeks' gestation. One fair-quality prospective cohort studyof early screening and treatment for gestational diabetes wasidentified, and its results suggest that an early diagnosisof gestational diabetes may represent pregestational diabetesbecause women with early diagnosis (by an abnormal result ona 50-g glucose challenge test at the first prenatal visit) weremore likely to require insulin and had a higher proportion ofhypertension, perinatal deaths, and neonatal hypoglycemia thanthose with diagnosis at 24 to 28 weeks' gestation (13).
Potential Harms of Screening or Treatment
There are 2 potential domains of harms of screening for andtreatment of gestational diabetes: the psychological and thephysical. The primary adverse effects associated with screeningwould be the psychological effect of screening on the motherwith gestational diabetes, and potentially on the mother whodoes not have gestational diabetes but has the added time, cost,physical discomfort, and psychological burden of screening andconfirmatory diagnostic testing. A review of the literaturerevealed mixed available evidence on the initial psychologicalimpact of gestational diabetes screening. In the first few weeksafter screening, women who screened positive for gestationaldiabetes may report higher anxiety, more psychological distress,and poorer perceptions of their general health than women whoscreened negative. Available evidence, however, suggests thatthese differences, even if present shortly after diagnosis,do not persist into the late third trimester or the postpartumperiod (14–16).
Further, ACHOIS found, in a subgroup that responded to the questionnaire,that treatment was potentially associated with overall improvedself-reported health status and reduced postpartum depressionat 3 months after birth compared with no treatment (11). Alternativeexplanations for the reduced postpartum depression and improvedquality-of-life responses in the treated group could includeunblinding before the 3 months' postpartum period before thequestionnaire was completed or what is sometimes termed theHawthorne effect, in which the additional attention given tothe treatment group, rather than the treatment itself, couldimprove perceptions. Finally, a prospective study found thatmood did not differ in women treated for gestational diabetescompared with controls (17).
For the mother, hypoglycemia is the potentially most seriousphysical harm. Not all studies monitored or reported maternalhypoglycemia, but in those that did, the rates are low withtreatment and no worse with alternate therapies.
With regard to potential fetal or newborn risks, the potentialteratogenicity of certain newer treatments for gestational diabetes(oral hypoglycemic agents or insulin analogues) presents a potentialphysical harm to the fetus that clearly could relate to gestationaldiabetes treatment; however, most treatments for gestationaldiabetes start in the second trimester, after the period ofmajor organogenesis. Thus, data are very limited to assess potentialteratogenicity of newer agents for treatment.
One potential issue is the number of false-positive screeningtest results. Given the lack of evidence to determine the accuracyof screening tests, it is difficult to estimate how often thisoccurs. However, studies show that fewer than 1 in 5 women witha positive glucose challenge test result will meet criteriafor gestational diabetes on a full oral glucose tolerance test(13). This result indicates that many women are being inconvenienced,that health care services are being used unnecessarily, andthat time is wasted evaluating false-positive test results.
Estimate of the Magnitude of Net Benefit
The USPSTF was unable to estimate the magnitude of net benefit,or indeed the existence of a benefit, of screening for or treatmentof gestational diabetes. This was due to a lack of studies ofscreening with a sufficient number of participants to permitevaluation of important health outcomes, such as mortality;brachial plexus injury; clavicular fracture; and admission toneonatal intensive care units for hypoglycemia, hyperbilirubinemia,or the respiratory distress syndrome. In addition, because ofthe lack of an accepted gold standard for screening, evidenceon the accuracy of available screening strategies is limited.There is also insufficient evidence on the benefits of treatinggestational diabetes in improving health outcomes.
How Does Evidence Fit with Biological Understanding?
Data on the overall impact of gestational diabetes screeningand treatment are limited because most babies with macrosomiaare born to mothers without gestational diabetes, and most casesof injuries related to shoulder dystocia occur in pregnancieswith infants of normal birthweight (18). The relationship betweengestational diabetes and adverse outcomes is further confoundedby the fact that maternal obesity is an independent risk factorfor many of the same outcomes (18).
Recommendations of Others
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Appendix: U.S. Preventive Services Task Force
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are Ned Calonge,MD, MPH, Chair (Colorado Department of Public Health and Environment,Denver, Colorado); Diana B. Petitti, MD, MPH, Vice Chair (KeckSchool of Medicine, University of Southern California, SierraMadre, California); Thomas G. DeWitt, MD (Children's HospitalMedical
Center, Cincinnati, Ohio); Leon Gordis, MD, MPH, DrPH(Johns Hopkins Bloomberg School of Public Health, Baltimore,Maryland);
Kimberly D. Gregory, MD, MPH (Cedars-Sinai MedicalCenter, Los Angeles, California); Russell Harris, MD, MPH (Universityof
North Carolina School of Medicine, Chapel Hill, North Carolina);George Isham, MD, MS (HealthPartners, Minneapolis, Minnesota);Michael
L. LeFevre, MD, MSPH (University of Missouri Schoolof Medicine, Columbia, Missouri); Carol Loveland-Cherry, PhD,RN (University
of Michigan School of Nursing, Ann Arbor, Michigan);Lucy N. Marion, PhD, RN (School of Nursing, Medical Collegeof Georgia,
Augusta, Georgia); Virginia A. Moyer, MD, MPH (Universityof Texas Health Science Center, Houston, Texas); Judith K. Ockene,PhD
(University of Massachusetts Medical School, Worcester,Massachusetts); George F. Sawaya, MD (University of California,San
Francisco, California); Albert L. Siu, MD (Mount Sinai Schoolof Medicine, New York, New York); Steven M. Teutsch, MD, MPH(Merck
& Co., West Point, Pennsylvania); and Barbara P.Yawn, MD, MSPH, MSc (Olmsted Medical Center, Rochester, Minnesota).
Members of the Task Force at the time this recommendation wasfinalized. For a list of current Task Force members, go to http://www.ahrq.gov/clinic/uspstfab.htm.
Author and Article Information
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Disclaimer: Recommendations made by the USPSTF are independentof the U.S. government. They should not be construed as an officialposition of the Agency for Healthcare Research and Quality orthe U.S. Department of Health and Human Services.
Potential Financial Conflicts of Interest: None disclosed.
Requests for Single Reprints: Reprints are available from theAgency for Healthcare Research and Quality Web site (http://www.preventiveservices.ahrq.gov).
* For a list of the members of the U.S. Preventive Services TaskForce, see the Appendix.
References
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