Task Force Recommends Universal Screening for GDM at 24 Weeks

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.

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 for preeclampsia, fetal macrosomia, and shoulder dystocia. When these outcomes are considered collectively, there is a moderate net benefit for the 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.

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).

These recommendations apply to pregnant women who have not been previously diagnosed with type 1 or 2 diabetes mellitus.

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 of 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.

A 2-step approach is commonly used in the United States. 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 mg/dL, 135 mg/dl, 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. Alternatively, a 75-g glucose load is administered after fasting glucose and plasma glucose levels are evaluated after 1 and 2 hours (1-step approach). A diagnosis of GDM is made when 2 or more glucose values fall at or above the specified glucose thresholds.

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.

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 factor–based 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).