No differences seen in outcomes with one-step vs. two-step gestational diabetes screening

One-step screening for gestational diabetes with a single two-hour glucose tolerance test found more cases but was not associated with improved outcomes when compared with two-step screening, a recent study found.

Researchers performed a pragmatic randomized trial comparing one-step and two-step screening for gestational diabetes among pregnant women in two Kaiser Permanente health systems. In one-step screening, patients fasted, then underwent a two-hour glucose tolerance test with a blood glucose level obtained after oral administration of a 75-g glucose load. In two-step screening, nonfasting patients underwent a one-hour glucose challenge test with a glucose level obtained after oral administration of a 50-g glucose load. If that result was positive, patients fasted and had a second visit to undergo a three-hour oral glucose tolerance test with a 100-g glucose load. Treatment of gestational diabetes was based on national guidelines and did not vary by screening approach. The study's primary outcomes were a diagnosis of gestational diabetes, large-for-gestational-age infants, a perinatal composite outcome (stillbirth, neonatal death, shoulder dystocia, bone fracture, or any arm or hand nerve palsy related to birth injury), gestational hypertension or preeclampsia, and primary cesarean section. The results of the trial were published March 11 by the New England Journal of Medicine.

Overall, 23,792 women were randomly assigned in a 1:1 ratio from May 2014 through December 2017 to receive one- or two-step screening; women who were pregnant more than once during the trial could be assigned to more than one screening type. Adherence to assigned screening was 66% in the one-step group (7,880 of 11,922 women) and 92% in the two-step group (10,881 of 11,870 women), with gestational diabetes diagnosed in 16.5% and 8.5%, respectively (unadjusted relative risk [RR], 1.94; 97.5% CI, 1.79 to 2.11). Respective incidences of the other primary outcomes in intention-to-treat analyses were not significantly different between groups: 8.9% and 9.2% for large-for-gestational-age infants (RR, 0.95; 97.5% CI, 0.87 to 1.05), 3.1% and 3.0% for the perinatal composite outcome (RR, 1.04; 97.5% CI, 0.88 to 1.23), 13.6% and 13.5% for gestational hypertension or preeclampsia (RR, 1.00; 97.5% CI, 0.93 to 1.08), and 24.0% and 24.6% for primary cesarean section (RR, 0.98; 97.5% CI, 0.93 to 1.02).

The researchers noted that the lower adherence rate in the one-step group biased the results toward the intention-to-treat analyses, that the two health systems used slightly different blood glucose thresholds when determining the need for a glucose tolerance test in the two-step group, and that clinicians were not blinded to patients' assignment, among other limitations. They concluded that although more cases of gestational diabetes were diagnosed with the one-step approach, risks for the primary outcomes did not differ between groups.

An accompanying editorial concluded that the study did not find enough benefit to the single-step approach appear to justify the diagnosis of more patients. “Refocusing attention on interventions in women who are at risk for the development of diabetes is more likely to yield substantive benefits,” it said.

On Feb. 16, the U.S. Preventive Services Task Force released a draft recommendation statement on screening for gestational diabetes, with a grade B recommendation in favor of screening asymptomatic patients at or after 24 weeks of gestation. The Task Force said that current evidence is insufficient to make a recommendation regarding earlier screening.

The statement is available for public comment until March 15.