One-Step Gestational Diabetes Diagnosis of Little Benefit

Tara Haelle

September 27, 2018

Gestational diabetes diagnoses shot up 41% after a healthcare system switched from recommending a two-step to a one-step screening method — but without clinically identifiable benefits to mothers or newborns —finds a new study published in the October issue of Obstetrics and Gynecology.

"An increase would be expected given the one-step approach's lower threshold for diagnosis," Gaia Pocobelli, PhD, of the Kaiser Permanente Washington Health Research Institute, Seattle, and colleagues acknowledge in their article.

Labor induction, neonatal hypoglycemia, nonstress testing, and insulin use all increased after the guideline change.

"The increases in labor induction and nonstress testing are also both plausible given it is recommended that women with gestational diabetes, especially those taking insulin, receive antenatal fetal surveillance and be induced by a certain gestational age as a result of their increased risk of adverse outcomes," they add.

And yet, "there was no apparent benefit regarding other maternal and neonatal outcomes" from the guideline switch, the authors report.

Diagnose More Diabetes, Look for More Problems...

In 2010, the International Association of Diabetes and Pregnancy Study Groups proposed a new "looser" criteria for diagnosing gestational diabetes requiring one abnormal glucose value during an oral glucose tolerance test (Diabetes Care. 2010;33:676-682). The criteria were adopted by the World Health Organization and American Diabetes Association, but not the American College of Obstetricians and Gynecologists, which still advises using the stricter "two-step" Carpenter-Coustan criteria that require two abnormal glucose values.

In their study, Pocobelli and colleagues compared outcomes among 4977 women screened for gestational diabetes from January 2009 to March 2011 — when clinicians predominantly used a two-step guideline — to outcomes of 6337 women screened April 2012 to December 2014 — after the Kaiser Permanente system in Washington switched to one-step gestational diabetes screening.

To control for potentially confounding time trends, the researchers also compared outcomes among 7840 women — 3386 during the first timeframe and 4454 during the second — whose prenatal care was provided by external healthcare practitioners and therefore not affected by the guideline change, so they effectively acted as a control group.

After the guideline change, one-step screening became the most common approach, used by 87% of internal Kaiser Permanente providers. A simultaneous near-quadrupling of insulin use, from 1.2% to 4.4%, accompanied the shift, and gestational diabetes diagnoses increased 65%, from 6.9% to 11.4%, the researchers found.

In absolute terms, labor induction rates also increased, though less dramatically, from 25.2% to 28.6%, and neonatal hypoglycemia jumped from 1.3% to 2%. Outpatient nonstress testing increased from 134.6 to 157 test days/100 women before and after the intervention.

Pocobelli and coauthors then calculated relative risk differences in outcomes after accounting for background time trends seen in the control group.

The guideline change from two-step to one-step screening was linked to a 41% greater likelihood for a gestational diabetes diagnosis among those assessed in the second time period (relative risk, 1.41).

The switch also accompanied a greater likelihood of labor induction (20% increase), neonatal hypoglycemia (77% increase), and nonstress testing (12% increase/100 women), again after adjustment for the background time trends in the control group.

The guideline change was not linked to any differences in risk for cesarean delivery or macrosomia.

The higher neonatal hypoglycemia incidence may have been influenced by surveillance bias, the authors point out, or resulted from the increased insulin use.

"Because pediatric guidelines recommend routine screening in neonates born to women with gestational diabetes, the increase we observed may have simply been the result of a greater proportion of neonates being screened because more women were diagnosed with gestational diabetes with the one-step approach, as opposed to a true increase in risk," they write.

"Women with gestational diabetes treated with insulin are 58% more likely than those treated with metformin to give birth to a neonate who develops hypoglycemia," they add.

One-Step Screening May Not Be Catching Women Most At Risk

Past research has found both net benefit and net harm linked to switching from two-step to one-step screening.

Although this new study's findings do not settle the continuing professional debate over the risks, benefits, and harms of the two screening methods, it does seem to be one of the first to account for time trends in the general population that occurred independently of the healthcare system's screening recommendations.

Still, the work could not account for other potentially influential confounding factors, including maternal diet and exercise trends, and underreported behaviors such a smoking. The use of electronic data to identify outcomes may also have led to some misclassification, the authors write.

"Our results may have been influenced by other changes in care included in the guideline such as lower blood glucose thresholds for recommending medication and an emphasis on insulin as first-line medication," they add.

Despite the intent for the one-step method to decrease risk of adverse outcomes, such as macrosomia and cesarean delivery, one-step screening may not be catching the population most at risk, the authors suggest.

"The additional women identified with the one-step approach may be at lower risk of these outcomes and may not benefit from gestational diabetes treatment to the same degree as women diagnosed with the two-step approach," they indicate.

"Overall, our findings do not suggest a benefit of adopting the one-step over the two-step approach," they conclude, noting that Kaiser Permanente Washington has now returned to using two-step screening.

"We recommend that any healthcare system considering switching to the one-step approach incorporate a rigorous evaluation of changes in maternal and neonatal outcomes."

The research was funded by the Group Health Foundation's Momentum Fund. One author (Yu) reported grant funding from Amgen and Bayer, and two authors (Pocobelli and Dublin) reported grant funding from Jazz Pharmaceuticals.

Obstet Gynecol. 2018;132:859-867. Abstract

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