Screening for Gestational Diabetes Beneficial in Asymptomatic Pregnant Women

Karina W. Davidson, PhD

Traditional diagnostic criteria puts the risk of gestational diabetes at 5.8% - 9.2%, with pregnant people with gestational diabetes at an increased risk for maternal and fetal complications and long-term health outcomes.

A new recommendation statement from the US Preventive Services Task Force Recommendation Statement (USPSTF) resulted in a systematic review to evaluate the accuracy, benefits, and harms of screening for gestational diabetes.

A team of investigators, led by Karina W. Davidson, PhD, Feinstein Institutes for Medical Research, noted moderate net benefit for gestational diabetes screening in asymptomatic pregnant persons at 24 weeks of gestation or after, but current evidence is insufficient to assess the benefits for screening before the time period of 24 weeks.

Patient Population

The statement targeted a pregnant population that had not been previously diagnosed with type 1 diabetes (T1D) or type 2 diabetes (T2D).

Increased risk for developing gestational diabetes included obesity, maternal age, history of gestational diabetes, family history of diabetes, and belonging to racial/ethnic groups with an increased risk of T2D.

A 2-step screening test followed by a diagnostic test or 1-step diagnostic test used for all patients, where the 50-g oral glucose challenge test (OGCT) is performed between 24 - 28 weeks to determine the fasting glucose level.

In the 1-step approach, a 75-g glucose load is administered after a fasting glucose level is obtained by the team and glucose levels are evaluated after 1 - 2 hours.

Initial treatment recommendations include moderate physical activity, dietary changes, support from diabetes educators and nutritionists, followed by medications if glucose is not controlled.

Update

In order to update the 2014 recommendation, a systematic review to evaluate the accuracy, benefits, and harms of screening for gestational diabetes, with the benefits and harms of treatment for pregnant persons and infants was performed.

The USPSTF performed a review of 45 prospective studies that assessed accuracy of screening tests for gestational diabetes.

In doing so, the accuracy of fasting plasma glucose level was evaluated against Carpenter and Coustan, IADPSG, and NDDG diagnostic criteria. Glucose level screening had an 90-mg/dL cutoff for a diagnosis for Carpenter and Coustan criteria, as well as IADPSG criteria.

They noted that HbA1c concentration was not associated with high sensitivity and specificity at any threshold.

Benefits of Early Detection

In determining the direct benefits or harms of screening for gestational diabetes, 2 newer RCTs found outcome benefits in full-term stillbirth and a reduction in risk of cesarean delivery, birth injuries, and NICU admissions. However, the team noted the small numbers of studies and lack of consistencies limit the impact of the findings.

Furthermore, 5 RCTS found screening with IADPSG criteria identified more cases, in comparison to Carpenter and Coustan screening criteria.

They observed treatment of gestational diabetes at 24 weeks of gestation or after was associated with a decreased risk of primary cesarean deliveries (relative risk RR, 0.70; 95% CI, 0.54 - 0.91).

In addition, the investigators observed for fetal outcomes, treatment of gestational diabetes at 24 weeks of gestation or after was associated with reduced risk of shoulder dystocia (RR, 0.42; 95% CI, 0.23 - 0.77), macrosomia (RR, 0.53; 95% CI, 0.41 - 0.68), LGA infants (RR, 0.56; 95% CI, 0.47 - 0.66), birth injury(odds ratio, 0.33; 95% CI, 0.11 - 0.99), and NICU admissions (RR, 0.73; 95% CI, 0.53 - 0.99).

They found harms associated with the treatment of gestational diabetes were evaluated in 13 trials, which determined treatment at 24 weeks of gestation or after was not associated with an increased risk for severe maternal hypoglycemia, low birth weight, or small for gestational age infants.

Further, the treatment of gestational diabetes was associated with a reduced risk of macrosomia (>4000 g) (RR, 0.53; 95% CI, 0.41 - 0.68), but no difference in risk of total number of cesarean deliveries (RR 0.95; 95% CI, 0.83 - 1.08).

Research Needs

As a last measure, the USPSTF noted gaps in evidence for further research on the topic.

This included a desire for more RCTs on the effect of screening for gestational diabetes and health outcomes, as well as studies to examine the benefit and harm of screening for and treatment of gestational diabetes in pregnant patients before 24 weeks of gestation.

In addition, they observed a gap in studies reporting on screening when defined by race/ethnicity, age, and other socioeconomic factors and a gap in studies on the potential harms of screening and treatment.

Further, they noted the need for greater consistency in diagnostic criteria and outcome definitions, more studies that report maternal health outcomes, and longer-term outcomes, including obesity and impaired fasting glucose, for both pregnant women and children.

Conclusion

Corresponding to calls for guidance of screening for prediabetes in pregnancies aside from gestational diabetes, investigators noted the difficulties in determining differences between the 2 groups.

“The USPSTF recognizes the difficulty in distinguishing between gestational diabetes and previously undiagnosed diabetes; however, detection and management of preexisting diabetes during pregnancy is beyond the scope of this recommendation,” investigators wrote. “Clinicians should continue to use their clinical judgment to determine if screening is appropriate for individual patients.”

The recommendation statement, “Screening for Gestational Diabetes: US Preventive Services Task Force Recommendation Statement,” was published online by JAMA.