Single-Step Screening Detects More Cases of Gestational Diabetes

gestational diabetes
gestational diabetes
Universal screening for gestational diabetes is commonly accepted, but few experts agree on whether one-step or two-step screening is best.

Gestational diabetes affects 6-9% of women and can increase the risk of stillbirth and neonatal death. While there is no consensus on how best to diagnose gestational diabetes, the American Diabetes Association prefers a one-step screening approach and the American College of Obstetricians and Gynecologists recommends the two-step Carpenter–Coustan screening approach.

Neither screening approach hold significant differences in terms of risk for perinatal and maternal complications, write researchers in the March 11 issue of the New England Journal of Medicine. However, the study did find “robust evidence” that single-step screening, as compared to the two-step test, can detect 1 in 5 cases of gestational diabetes.

Led by Teresa A. Hillier, MD, of the Center for Health Research at Kaiser Permanente Northwest Interstate in Oregon, researchers conducted a randomized trial comparing a one-step glucose-tolerance test and a two-step glucose challenge.

The study included 23,792 women who were assigned to either the one-step or two-step screening groups. The primary outcomes were a diagnosis of gestational diabetes, large-for-gestational-age infants, gestational hypertension, preeclampsia, primary cesarean section or a perinatal composite outcome including stillbirth, neonatal death, shoulder dystocia, bone fracture, or any arm or hand nerve palsy related to birth injury.

In the one-step screening test, each of the women received a glucose tolerance test using the 75-g glucose load. For the two-step screening test, the women received a 50-g glucose load. Gestational diabetes was diagnosed in 16.5% of the women who received one-step screening as compared to 8.5% who received two-step screening (unadjusted relative risk, 1.94; 97.5% confidence interval [CI], 1.79 to 2.11).

Fewer women in the one-step screening group achieved the primary outcome of large-for-gestational-age infants:  8.9% as compared to 9.2% in the two-step screening group (relative risk, 0.95; 97.5% CI, 0.87 to 1.05). For perinatal composite outcomes, the rates were 3.1% and 3.0%, respectively for the one-step and two-step groups (relative risk, 1.04; 97.5% CI, 0.88 to 1.23). The numbers for gestational hypertension were comparable with 13.6% and 13.5% of women in the two groups developing preeclampsia (relative risk, 1.00; 97.5% CI, 0.93 to 1.08). The numbers were also similar for women in the two groups needing primary cesarean section with 24.0% and 24.6%, respectively, of women receiving the procedures (relative risk, 0.98; 97.5% CI, 0.93 to 1.02).

“In our large randomized trial, one-step screening, as compared with two-step screening, doubled the incidence of the diagnosis of gestational diabetes but did not affect the risks of large-for-gestational-age infants, adverse perinatal outcomes, primary cesarean section, or gestational hypertension or preeclampsia,” the authors wrote.

Several limitations were noted with this study including the underrepresentation of some racial and ethnic groups in which gestational diabetes is more common. Nor, did the study address the potential of risk-reduction strategies for high risk women.

Writing in an editorial that accompanied the study, Brian Casey, MD, of the University of Alabama, addressed the need for an agreement on screening for gestational diabetes. “Despite decades of research on gestational diabetes, however, there is still no agreement regarding the best approach to the diagnosis of gestational diabetes,” he wrote. “Refocusing attention on interventions in women who are at risk for the development of diabetes is more likely to yield substantive benefits.”


  1. Teresa A. Hillier, M.D., Kathryn L. Pedula, M.S., Keith K. Ogasawara, M.D., et al. “A Pragmatic, Randomized Clinical Trial of Gestational Diabetes Screening,” New England Journal of Medicine. March 11, 2021;384:895-904.DOI: 10.1056/NEJMoa2026028
  2. Brian Casey, M.D. “Gestational Diabetes — On Broadening the Diagnosis,” New England Journal of Medicine. March 11, 2021; 384:965-966 DOI: 10.1056/NEJMe2100902