One-Step vs Two-Step Screening: Which is Better for Gestational Diabetes?

One-step screening for gestational diabetes boosted diagnoses versus two-step screening but ultimately did not have a meaningful impact on risks for adverse outcomes, such as large-for-gestational-age infants or pre-eclampsia, according to results from the ScreenR2GDM trial.

In the pragmatic trial conducted among nearly 24,000 women at healthcare systems in Oregon and Hawaii, gestational diabetes was diagnosed in 16.5% of the women assigned to the one-step group and in 8.5% of those assigned to the two-step group (unadjusted relative risk 1.94, 97.5% CI 1.79-2.11), reported Teresa A. Hillier, MD, of the Center for Health Research at Kaiser Permanente Northwest in Portland, Oregon, and co-authors.

In intention-to-treat (ITT) analyses, the incidences of primary outcomes included:

• Large-for-gestational-age infants: 8.9% for the one-step group and 9.2% for the two-step group (relative risk 0.95, 97.5% CI 0.87-1.05)
• Gestational hypertension or preeclampsia: 13.6% and 13.5% (RR 1.00, 97.5% CI 0.93-1.08)

While the authors noted in the New England Journal of Medicine that “There was lower adherence to screening with the fasting one-step approach… the results were similar in analyses that accounted for differences in adherence.”

The ScreenR2GDM trial design was described in 2019, with the authors defining the screening protocols as:

• One-step screening: glucose-tolerance test with blood glucose level obtained after the oral administration of a 75-g glucose load in the fasting state.
• Two-step screening: glucose challenge test with blood glucose level obtained after the oral administration of a 50-g glucose load in the non-fasting state. If positive, this was followed by an oral glucose-tolerance test with a 100-g glucose load in the fasting state.

There is currently no consensus on the best way to diagnose gestational diabetes, Hillier’s group explained — for example, the American Diabetes Association supports the one-step method while the American College of Obstetricians and Gynecologists prefers two-step Carpenter-Coustan screening.

In an editorial accompanying the study, Brian Casey, MD, of the University of Alabama at Birmingham, noted that in 2010, the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) backed a “single-step approach to the diagnosis of gestational diabetes with the use of thresholds associated with a risk of these perinatal outcomes that was 1.75 times as high as the mean fasting, 1-hour, and 2-hour plasma glucose concentrations.”

The IADPSG estimated that this approach would “double or triple the incidence of gestational diabetes diagnoses over traditional two-step screening,” he explained.

However, “The current trial provides robust evidence that single-step, as compared with two-step, gestational diabetes screening resulted in the detection of gestational diabetes in almost one in five pregnant women, with no apparent maternal or perinatal benefit overall,” Casey said.

While ScreenR2GDM suffered from underrepresentation of some racial or ethnic groups — more than half of both screening groups were White — and a lack of data on women at high risk for gestational diabetes, the single-step approach still seems to be “insufficient to justify the associated patient and health care costs of broadening the diagnosis,” he stated.

The trial randomized 23,792 women 1:1 to either one- or two-step screening, and a total of 94% completed screening — 66% of those randomized to one-step screening versus 92% of those assigned to two-step screening. The groups were similar in terms of demographics, such as age (around 30), BMI (about 28 kg/m²) and race (55% White; 15% Asian; about 3% Black). Oregon enrolled almost 69% of the patients versus about 31% in Hawaii. Approximately 8% of women in both groups had previous hypertension while about 5% had previous gestational diabetes. More than 45% in both groups experienced gestational weight gain exceeding National Academy of Medicine guidelines, the authors noted.

They reported the incidences of other outcomes:

• Perinatal composite outcome: 3.1% and 3.0% (RR 1.04, 97.5% CI 0.88-1.23).
• Primary cesarean section: 24.0% and 24.6% (RR 0.98, 97.5% CI 0.93-1.02).
• Receipt of insulin or hypoglycemic medication for a gestational diabetes diagnosis: 42.6% and 45.6%.

Also, in a prespecified analysis limited to women with a diagnosis of gestational diabetes, the incidences of the trial outcomes were similar between the groups, they noted, with the diagnosis in 39% of the one-step screening group based only on the isolated fasting plasma glucose level. Half of these women “met the criteria for gestational diabetes with an isolated fasting plasma glucose level in the range of 92 to 94 mg per deciliter… thus, their glucose levels at diagnosis were already within the target range for treatment (fasting plasma glucose level <95 mg per deciliter),” Hillier’s group wrote.

They also pointed out that, in the 6% of pregnancies in women who did not undergo screening, the outcomes appeared to be worse than those in either of the screened groups, but “these findings are probably explained at least in part by other differences between women who adhered to recommended screening and those who did not.”

Study limitations included the fact that the sites used “slightly different thresholds for the glucose challenge test to determine whether women in the two-step group should receive an oral glucose-tolerance test,” according to the authors.

Hillier and co-authors noted that the ongoing GDM2 trial (for which some results are available) should shed more light on the pros and cons of one-step versus two-step screening. In the meantime, they called attention to two issues. First, there is “the burden on individual women of receiving a diagnosis of gestational diabetes on the basis of these milder criteria [with one-step screening] and the burden on the system of treating many more women.” Second, previous research has indicated that “maternal gestational diabetes may be a risk factor for childhood obesity and metabolic sequelae, so treating more women could have long-term benefits.”

1. One-step screening for gestational diabetes led to more diagnoses versus two-step screening.

2. There were no significant between-group differences between one-step and two-step screening in terms of risks of the primary outcomes relating to perinatal and maternal complications.

Shalmali Pal, Contributing Writer, BreakingMED™

Cat ID: 191

Topic ID: 83,191,730,187,723,191,41,192,925