Clinicians should continue to screen for gestational diabetes in all asymptomatic pregnant patients during the second trimester, according to a recommendation from the U.S. Preventive Services Task Force (USPSTF).

Providers should screen for gestational diabetes at 24 weeks’ gestation or later to improve maternal and fetal outcomes (grade B recommendation), stated Karina W. Davidson, PhD, MASc, of the Feinstein Institutes for Medical Research in New York, and task force colleagues in JAMA.

The task force found adequate evidence that screening for gestational diabetes betters maternal and infant health, and treatment — which can include both dietary and medical therapies — is associated with improvements in outcomes including primary cesarean delivery, macrosomia, large for gestational age infants, and birth injuries.

However, the task force stated that there was insufficient evidence to recommend for or against gestational diabetes screening before 24 weeks of pregnancy (I statement).

In an accompanying editorial, Cuilin Zhang, MD, PhD, MPH, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development in Bethesda, and Patrick Catalano, MD, of Tufts Medical Center in Boston, agreed that there is “inadequate evidence that commonly used screening tests can accurately detect glucose intolerance in early pregnancy.”

Some studies have used levels of nonfasting plasma saturated fatty acids in early pregnancy or liquid chromatography and mass spectrometry measures of metabolomics from urine samples to accurately identify gestational diabetes in earlier gestations, Zhang and Catalano noted. Although these studies need replicating, the editorialists added that “they provide the first proof of the concept that an algorithm incorporating novel biomarkers and metabolomics profile in early pregnancy can accurately identify gestational diabetes.”

“Effective early screening to identify women at high risk for gestational diabetes and timely intervention may represent an important approach,” Zhang and Catalano wrote. “More studies — in particular, randomized clinical trials that evaluate the long-term health outcomes of early screening, intervention, and treatment — are warranted to inform future recommendations.”

Gestational diabetes was estimated to occur in 5.6% to 9.2% of all pregnant women in the U.S. from 2007 to 2016, but prevalence might be up to three times as high depending on the diagnostic criteria used, the task force stated. While gestational diabetes is usually asymptomatic, it may cause maternal and fetal complications, such as preeclampsia, fetal macrosomia, and neonatal hypoglycemia.

The recommendation from the USPSTF concurs with previous 2014 guidance on screening for gestational diabetes, which also recommended universal screening after 24 weeks. These recommendations are largely consistent with medical organizations including the American College of Obstetricians and Gynecologists, the NIH, the American Diabetes Association, the Endocrine Society, and the American Academy of Family Physicians, although there are some discrepancies on screening tool preference.

The task force recommended clinicians screen for gestational diabetes between 24 and 28 weeks’ gestation, using a two-step approach of both a screening tool (oral glucose challenge test) and diagnostic (oral glucose tolerance test), just the oral glucose tolerance test, or fasting plasma glucose tests.

The new recommendation is based on an evidence report by Jennifer Pillay, MSc, of the University of Alberta in Edmonton, Canada, and colleagues. They evaluated 76 studies investigating practices around gestational diabetes screening. This included around 20 studies carried over from the previous USPSTF review, and more than 50 new studies.

According to findings from the evidence report, also in JAMA, at 24 weeks’ gestation or later, oral glucose challenge tests with 140- and 135-mg/dL cutoffs had sensitivities of 82% and 93%, respectively, and specificities of 82% and 79%, respectively, against Carpenter and Coustan criteria.

An oral glucose challenge test with a 140 mg/dL cutoff had sensitivity of 85%, and a specificity of 81% against the National Diabetes Group Data criteria.

One-step or two-step screening was not associated with any significant differences in many maternal and fetal outcomes.

Pregnant people who received treatment for for gestational diabetes had a lower risk of primary cesarean deliveries (RR 0.70, 95% CI 0.54-0.91), shoulder dystocia (RR 0.42, 95% CI 0.23-0.77), macrosomia (RR 0.53, 95% CI 0.41-0.68), large for gestational age (RR 0.56, 95% CI 0.47-0.66), birth injuries (OR 0.33, 95% CI 0.11-0.99), and NICU admissions (RR 0.73, 95% CI 0.53-0.99).

No randomized clinical trials assessed direct benefits or harms of screening for gestational diabetes.

Potential harms of screening may include mental health issues such as depression or anxiety, intensive medical intervention, or negative hospital experiences (such as lower rates of breastfeeding in the first hour or rates of newborns staying in the room with their mothers) that may be associated with a gestational diabetes diagnosis.

Additionally, some risks associated with treatment include neonatal or maternal hypoglycemia, increased risk of small-for-gestational-age infants, or maternal stress. There was no risk of harm from treatment at 24 weeks’ gestation or later.

The USPSTF identified several knowledge gaps in their review, calling for more research around the effect of screening for gestational diabetes and health outcomes, the benefits and harms of earlier screening, socioeconomic factors, and screening strategies. It also identified a need for further studies on potential harms of both screening and treatment.