Grade: I The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the service. Evidence is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined.
The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for GDM in asymptomatic pregnant women before 24 weeks of gestation.
Frequency of Service
No information available.
Risk Factor Information
Several factors increase a woman's risk for developing GDM, including obesity, increased maternal age, history of GDM, family history of diabetes, and belonging to an ethnic group that has increased risk for developing type 2 diabetes mellitus (Hispanic, Native American, South or East Asian, African American, or Pacific Island descent). Factors associated with a lower risk for developing GDM include age younger than 25 to 30 years, white race, a body mass index (BMI) of 25 kg/m2 or less, no family history (that is, in a first-degree relative) of diabetes, and no history of glucose intolerance or adverse pregnancy outcomes related to GDM.
Patient Population Under Consideration
These recommendations apply to pregnant women who have not been previously diagnosed with type 1 or 2 diabetes mellitus.
Assessment of Risk
Several factors increase a woman's risk for developing GDM, including obesity, increased maternal age, history of GDM, family history of diabetes, and belonging to an ethnic group that has increased risk for developing type 2 diabetes mellitus (Hispanic, Native American, South or East Asian, African American, or Pacific Island descent).
Factors associated with a lower risk for developing GDM include age younger than 25 to 30 years, white race, a body mass index (BMI) of 25 kg/m2 or less, no family history (that is, in a first-degree relative) of diabetes, and no history of glucose intolerance or adverse pregnancy outcomes related to GDM.
There are 2 strategies used to screen for gestational diabetes in the United States. In the 2-step approach, the 50-g OGCT is performed between 24 and 28 weeks of gestation in a nonfasting state. If the screening threshold is met or exceeded (130, 135, or 140 mg/dL [7.21, 7.49, or 7.77 mmol/L]), patients receive the oral glucose tolerance test (OGTT). During the OGTT, a fasting glucose level is obtained, followed by administration of a 100-g glucose load, and glucose levels are evaluated after 1, 2, and 3 hours. A diagnosis of GDM is made when 2 or more glucose values fall at or above the specified glucose thresholds. Alternatively, in the 1-step approach, a 75-g glucose load is administered after fasting and plasma glucose levels are evaluated after 1 and 2 hours. Gestational diabetes is diagnosed if 1 glucose value falls at or above the specified glucose threshold.
Timing of Screening
Screening is recommended after 24 weeks of gestation. Screening for GDM may occur earlier than 24 weeks of gestation in high-risk women, but there is little evidence about the benefits and harms of screening before 24 weeks of gestation.
Initial treatment includes moderate physical activity, dietary changes, support from diabetes educators and nutritionists, and glucose monitoring. If the patient's glucose is not controlled after these initial interventions, she may be prescribed medication (either insulin or oral hypoglycemic agents), or have increased surveillance in prenatal care or changes in delivery management.
Suggestions for Practice Regarding the I Statement
In deciding whether to screen for GDM before 24 weeks of gestation, primary care providers should consider the following.
Potential Preventable Burden
Gestational diabetes affects about 240,000 (7%) of the 4 million annual births in the United States.3 Pregnant women with GDM are at increased risk for maternal and fetal complications and may benefit from early identification and treatment. Women with GDM are at increased risk of developing type 2 diabetes mellitus.
Potential harms of screening for gestational diabetes include psychological harms and intensive medical interventions (induction of labor, cesarean delivery, or admission to the neonatal intensive care unit). Possible adverse effects of treatment include neonatal or maternal hypoglycemia and maternal stress.
A cross-sectional study reported that universal screening is the most common practice in the United States, with 96% of obstetricians routinely screening for GDM.4 Some women are screened earlier than 24 weeks of gestation because they have risk factors for type 2 diabetes, such as obesity, family history of type 2 diabetes, or fetal macrosomia during a previous pregnancy.
If a pregnant woman presents in the first trimester or in early pregnancy with risk factors for type 2 diabetes, clinicians should use their clinical judgment to determine what is appropriate screening for that individual patient given her health needs and the insufficient evidence.
Other Approaches to Prevention
Most pregnant women should be encouraged to attain moderate gestational weight gain, based on their prepregnancy BMI, and to participate in physical activity based on their clinician's recommendations. The Institute of Medicine has made recommendations for weight gain during pregnancy based on prepregnancy BMI.5
Research Needs and Gaps
More research is needed to directly evaluate screening for GDM and maternal and infant health outcomes. Research is also needed to help determine the most beneficial glucose thresholds for a positive screen and treatment targets. Continued research is needed to examine alternative screening methods, such as glycosylated hemoglobin (HbA1c) measurement and risk factorÃ¢ÂÂbased assessment. Additional studies are needed to evaluate the effect of different treatments for GDM on longer-term metabolic maternal and infant outcomes, such as persistent maternal glucose intolerance after delivery and type 2 diabetes mellitus and obesity in the mother and infant. The use of a consistent strategy for screening for and diagnosing GDM in studies would allow for better comparisons of treatment outcomes across clinical trials.
The increasing prevalence of type 2 diabetes mellitus in women of reproductive age merits consideration of preconception screening for overt diabetes in women who are at risk for type 2 diabetes. Additional studies are needed to determine whether identifying and treating glucose intolerance before 24 weeks of gestation reduces maternal and fetal complications at delivery or leads to improved long-term health outcomes. For example, a follow-up to the Mild GDM Trial is examining whether different types of interventions in pregnant women with mild GDM decreases the risk for obesity in their children.6
Gestational diabetes mellitus is glucose intolerance discovered during pregnancy. The prevalence of GDM in the United States is 1% to 25%, depending on patient demographics and diagnostic thresholds.1 Pregnant women with gestational diabetes are at increased risk for maternal and fetal complications, including preeclampsia, fetal macrosomia (which can cause shoulder dystocia and birth injury), and neonatal hypoglycemia. Women with GDM are also at increased risk for developing type 2 diabetes mellitus; approximately 15% to 60% of women develop type 2 diabetes within 5 to 15 years of delivery.2 Screening for GDM generally occurs after the 24th week of pregnancy. Screening before 24 weeks may identify women with glucose intolerance earlier in pregnancy.
The USPSTF found adequate evidence that primary care providers can accurately detect GDM in asymptomatic pregnant women after 24 weeks of gestation. The most commonly used screening test in the United States is the 50-g oral glucose challenge test (OGCT).
Other methods of screening include the fasting plasma glucose test and screening based on risk factors. However, there is limited evidence on these alternative screening approaches. The USPSTF found inadequate evidence to compare the effectiveness of different screening tests or thresholds for a positive screen result.
Benefits of Detection and Early Treatment
The USPSTF found adequate evidence that treatment of screen-detected GDM with dietary modifications, glucose monitoring, and insulin (if needed) can significantly reduce the risk of preeclampsia, fetal macrosomia, and shoulder dystocia. When these outcomes are considered collectively, there is a moderate net benefit for both mother and infant. The benefit of treatment on long-term metabolic outcomes in women who are treated for GDM compared with those who are not treated is uncertain.
The USPSTF found inadequate evidence to determine whether there are benefits to screening for GDM in women before 24 weeks of gestation.
Harms of Detection and Early Treatment
Overall, the USPSTF found adequate evidence that the magnitude of the harms of screening and treatment is small to none. Randomized, controlled trials (RCTs) demonstrated an increase in the number of prenatal visits in screen-detected women who were treated for GDM compared with screen-detected women who were not treated. There was conflicting evidence on the risk for an increase in the induction of labor associated with treatment. No significant differences were reported for cesarean delivery or neonatal intensive care unit admissions between women who were treated and women who were not treated for GDM in the overall pooled meta-analysis. Trials also demonstrated no significant differences in the incidence of small-for-gestational-age infants or episodes of neonatal hypoglycemia, but the trials were not adequately powered to detect meaningful differences in these outcomes.
The USPSTF concludes with moderate certainty that there is a moderate net benefit to screening for gestational diabetes after 24 weeks of gestation to reduce maternal and fetal complications (the collective outcomes of preeclampsia, macrosomia, and shoulder dystocia).
The USPSTF concludes that the evidence on screening for gestational diabetes before 24 weeks of gestation is insufficient, and the balance of benefits and harms of screening cannot be determined.
Recommendations of OthersIn 2013, the American Congress of Obstetricians and Gynecologists recommended screening all pregnant women with a patient history or the 50-g OGCT.15 The American Diabetes Association endorses glucose testing for GDM in all pregnant women who do not have a prepregnancy diagnosis of diabetes between 24 and 28 weeks of gestation using a 75-g 2-hour OGTT with thresholds proposed by the International Association of Diabetes and Pregnancy Study Groups.16 In 2013, an independent panel supported by the National Institutes of Health Consensus Development Program considered whether using the 75-g OGTT (1-step approach), as proposed by the International Association of Diabetes and Pregnancy Study Groups and supported by the American Diabetes Association, should be adopted instead of the 2-step approach. The panel released a statement that there is not enough evidence to adopt a 1-step approach.17, 18 The American Academy of Family Physicians recommends screening for GDM in asymptomatic pregnant women after 24 weeks of gestation. It also concludes that the evidence is insufficient to assess the balance of benefits and harms of screening for GDM in asymptomatic pregnant women before 24 weeks of gestation.19 The Endocrine Society recommends universal screening for GDM using the OGTT at 24 to 28 weeks of gestation.20