Benefits Limited for Early Gestational Diabetes Screening

Tara Haelle

February 10, 2022

Screening pregnant women with obesity for gestational diabetes before 20 weeks of pregnancy did not lead to any improved maternal or neonatal outcomes compared with doing routine screening between 24 and 28 weeks, according to research presented Feb. 4 at the Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.

"There is increasing evidence that early screening does not reduce the risk of adverse perinatal outcomes," Jennifer Thompson, MD, associate professor of ob.gyn. at Vanderbilt University, Nashville, Tenn., said in an interview. "The increasing number of studies that have demonstrated no benefit in reducing adverse perinatal outcomes leads to consideration to revise recommendations for early screening."

However, she did note that early screening may be helpful in identifying patients with undiagnosed preexisting diabetes.

Michael Richley, MD, a maternal-fetal medicine fellow at the University of California, Los Angeles, said catching those previously undiagnosed cases is one of the goals of earlier screening with the expectation that earlier management will lead to better outcomes.

"If a patient then obtains the diagnosis of type 2 diabetes, introducing nutritional counseling and possible medical management early can lead to better outcomes," said Richley, who attended the presentation but was not involved in the research. "While catching undiagnosed type 2 diabetes is not common, it is becoming increasingly common lately."

Obesity is a known risk factor for impaired glucose metabolism and for gestational diabetes, explained presenter Christopher A. Enakpene, MD, an ob.gyn. from Midland, Tex., who completed the study while completing his maternal-fetal medicine fellowship at the University of Illinois in Chicago. Enakpene reminded attendees that the American College of Obstetricians and Gynecologists (ACOG) currently recommends early screening for gestational diabetes in patients with certain risk factors, including obesity, a history of first-degree relatives with diabetes, or a history of gestational diabetes, impaired glucose tolerance, poor pregnancy outcomes, fetal demise, congenital abnormalities, or birth of an infant large for gestational age.

The researchers screened 7,126 patients for enrollment in the study from March 2017 through February 2019 and identified 600 who met the criteria: An adult with a singleton pregnancy and body mass index (BMI) of at least 30 kg/m2. Patients were excluded if they had preexisting diabetes, elevated blood glucose or impaired glucose tolerance, a history of gestational diabetes, any chromosomal anomalies or abnormalities in the pregnancy, or were past 20 weeks of pregnancy.

The prospective randomized controlled trial was open label and included 296 patients who were randomly assigned to early screening with a 1-hour glucose challenge test (GCT) and hemoglobin A1c before 20 weeks, followed by a 3-hour oral glucose tolerance test if the GCT result was between 140 and 200 mg/dL with an HbA1c of less than 6.5%. The other 304 patients were screened with a 1-hour GCT between 24 and 28 weeks but also had an HbA1c test before 20 weeks.

The primary outcome was macrosomia, defined as a birth weight at least 4,000 g, with various maternal and neonatal secondary outcomes. The only significant difference between the groups at baseline was a higher proportion of Hispanic participants in the early screening group (22.4%) compared to the routine screening group (13.7%).

The groups had no significant differences in birth weight or macrosomia, which occurred in 2.8% of the early screening group and 3.4% of the routine screening group (P = .7). There were no significant differences in gestational age at delivery, preeclampsia, polyhydramnios, shoulder dystocia, cesarean delivery, or NICU admission. However, the rate of gestational diabetes was significantly higher in the early screening group (22.5%) than in the routine screening group (15.7%; P < .05). In addition, more participants with gestational diabetes in the early screening group used insulin (34.4%) compared with those in the routine screening group (15.6%; P < .05).

Enakpene noted several reasons that the perinatal outcomes may have been similar between the groups, such as the increased rate of gestational diabetes requiring treatment in the early screening group or a higher proportion of participants using insulin in the early screening group.

"Hence, the similarity in adverse perinatal outcomes between the groups despite a higher proportion of gestational diabetes in the early group might be due to more utilization of insulin," Enakpene said.

Richley was not surprised by the findings and hypothesized that the reason for not seeing a difference in outcomes might relate to using a 20-week cutoff for testing when type 2 diabetes would be evident at any stage of pregnancy.

"It would be interesting to have a study look at diabetes testing exclusively in the first trimester for high-risk patients that looks at neonatal outcomes and see if that would show a difference between the two groups," Richley said.

Thompson was similarly interested in whether 20 weeks was an early enough time for early screening.

"I would also like to know the differences in management between the two groups and if the knowledge of early diagnosis impacted their management, such as timing of medication start, amount of medication required, and how that differed from the standard group," Thompson said. "Since patients with a hemoglobin A1c > 6.5% or glucose tolerance test > 200 [mg/dL] were excluded, I'm interested in the number of patients that were excluded since they likely have undiagnosed preexisting diabetes, which are the patients that may benefit most from early screening."

Richley pointed out that the potential clinical implications of the study are limited right now.

"While their secondary outcomes of neonatal hypoglycemia, method of delivery, and other common obstetrical measures were not different, we cannot draw conclusions from this as the study was not powered to evaluate these findings," Richley said. "I do still see a role in early screening for patients with risk factors but favor doing so at the first prenatal visit, whenever that is, as opposed to as late as mid-second trimester, though this is often when a patient's first interaction with a health care system will be within their pregnancy."

Enakpene, Thompson, and Richley reported no disclosures. External funding for the study was not noted.

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