How Do Screening Methods for Gestational Diabetes Compare?

When comparing a 1-step approach with a 2-step approach for diagnosing gestational diabetes in a cohort of pregnant women, researchers found no significant between-group differences in the risks of primary outcomes relating to perinatal and maternal complications. Findings of the randomized clinical trial were published in The New England Journal of Medicine.¹

Gestational diabetes, which affects 6% to 25% of pregnant women, is associated with increased risks of stillbirth, neonatal death, and additional serious conditions in mothers and babies. Although universal gestational diabetes screening is recommended at 24 to 28 weeks' gestation, consensus about which of 2 recommended screening approaches should be used is lacking, the researchers wrote.

To best diagnose the condition “expert professional organizations acknowledge 2 acceptable options: The International Association of the Diabetes and Pregnancy Study Groups (IADPSG) 1-step screening approach (currently preferred by the American Diabetes Association) and the 2-step Carpenter–Coustan screening approach (recommended by the American College of Obstetricians and Gynecologists); both organizations note the need for additional evidence related to outcomes,” the authors explained.

To compare the approaches, they conducted a pragmatic, randomized clinical trial involving 23,792 pregnant women receiving care at Kaiser Permanente Northwest and Kaiser Permanente Hawaii. Women with more than 1 pregnancy during the trial window could have been assigned to more than 1 type of screening.

Between May 2014 and December 2017, all participants were randomly assigned 1:1 to undergo the 1-step or 2-step screening approach at their first prenatal visit. The study assessed 5 primary outcomes: diagnosis of gestational diabetes, large-for-gestational-age infants (defined as having a birthweight > 90th percentile), a composite measure of perinatal outcomes (stillbirth, neonatal death, etc), primary cesarean section, and gestational hypertension or preeclampsia.

Of the women included, 66% in the 1-step group and 92% in the 2-step group adhered to assigned screening protocols. Overall, 16.5% of the women in the 1-step approach received a gestational diabetes diagnosis compared with 8.5% of those in the 2-step group (unadjusted relative risk [RR], 1.94; 97.5% CI, 1.79-2.11).

Intention-to-treat analyses found the following respective incidences for other primary outcomes:

• Large-for-gestational-age infants, 8.9% (1-step) and 9.2% (2-step) (RR, 0.95; 97.5% CI, 0.87-1.05)
• Perinatal composite outcome, 3.1% and 3.0% (RR, 1.04; 97.5% CI, 0.88-1.23)
• Gestational hypertension or preeclampsia, 13.6% and 13.5% (RR, 1.00; 97.5% CI, 0.93-1.08)
• Primary cesarean section, 24.0% and 24.6% (RR, 0.98; 97.5% CI, 0.93-1.02)

“Results were materially unchanged in intention-to-treat analyses with inverse probability weighting to account for differential adherence to the screening approaches,” the researchers said. Analyses also showed outcomes of the 6% of pregnancies in women who did not undergo screening appeared to be worse than those in either screened cohort, but this finding may be due to other differences between women who adhered to recommended screenings and those who did not.

Among those with gestational diabetes, the percentages of those who received insulin of hypoglycemic medication were similar between the groups: 42.6% in the 1-step cohort and 45.6% in the 2-step cohort.

Lower adherence to the 1-step approach biased findings toward the planned intention-to-treat analyses, marking a limitation. Furthermore, sites included in the trial “used slightly different thresholds for the glucose challenge test to determine whether women in the 2-step group should receive an oral glucose-tolerance test; both blood glucose level thresholds (130 mg/dL and 140 mg/dL) are clinically recommended.”

Black and American Indian women were also not well represented in the trial, meaning generalization of results may be limited.

In addition, “the potential long-term benefits of increased diagnoses of gestational diabetes—such as the identification of more women at high risk for subsequent diabetes who might benefit from risk-reduction strategies—were not addressed by the trial,” Brian Casey, MD, wrote in an accompanying editorial.²

“On the basis of the current data, however, the perinatal benefits of the diagnosis of gestational diabetes with the use of the IADPSG single-step approach appear to be insufficient to justify the associated patient and health care costs of broadening the diagnosis,” he concluded. “Refocusing attention on interventions in women who are at risk for the development of diabetes is more likely to yield substantive benefits.”

References

1. Hillier TA, Pedula KL, Ogasawara KK, et al. A pragmatic, randomized clinical trial of gestational diabetes screening. N Engl J Med. Published online March 10, 2021. doi:10.1056/NEJMoa2026028

2. Casey B. Gestational diabetes—on broadening the diagnosis. N Engl J Med. Published online March 10, 2021. doi:10.1056/NEJMe2100902