Rise in gestational diabetes linked to changes in screening procedures

Key takeaways:

• In British Columbia, the screening process for gestational diabetes shifted from a two-step to a one-step approach from 2005 to 2019.
• The results highlight the importance of collecting data on screening practices to better understand rising trends in gestational diabetes worldwide.

An increase in the incidence of gestational diabetes in Canada was primarily explained by changes in screening methods as opposed to changes in population factors, including older maternal age, according to researchers.

Elizabeth Nethery, PhD, MSc, MSM, RM, a researcher from the School of Population and Public Health at the University of British Columbia, and colleagues wrote in the Canadian Medical Association Journal that the reasons for worldwide rises in gestational diabetes are poorly understood, but changes in screening procedures could be a potential explanation.

“Further, consensus is lacking on which method should be used to screen for gestational diabetes,” they wrote.

According to the researchers, national guidelines in Canada currently recommend a two-step screening approach consisting of a “1-hour, 50 g glucose challenge test, followed by a 2-hour, 75 g oral glucose tolerance test for patients who screen positive.” A one-step screening approach (a 2-hour, 75 g oral glucose tolerance test) is recommended as an alternative method.

“As 1-step screening is more sensitive than the 2-step approach, increased use of this method could be expected to increase the rate of diagnosis of gestational diabetes,” Nethery and colleagues wrote.

The researchers conducted a population-based cohort study to determine the role of screening practices on gestational diabetes incidence rates in British Columbia. They analyzed data from 551,457 pregnancies at or beyond 28 weeks’ gestation, which had a first glucose tolerance test screening between July 1, 2004, to June 30, 2019.

Nethery and colleagues found that gestational diabetes diagnoses increased from 7.2% in 2005 to 14.7% in 2019, and screening completions increased from 87.2% to 95.5% in during the same period.

Meanwhile, use of the one-step screening method rose from 0% in 2005 to 50.5% in 2012 but declined to 39.5% by 2019.

Overall, there was a 2.04-fold (95% CI, 1.94-2.13) increase in the risk for gestational diabetes in 2019 compared with 2005. The increased risk dropped to 1.89-fold (95% CI, 1.81-1.98) in 2019 after the researchers adjusted for the rise in screening completions. It further declined to a 1.34-fold (95% CI, 1.28-1.40) increased risk after the researchers accounted for screening methods.

Despite concerns about an increase in maternal age and BMIs of pregnant persons, Nethery and colleagues reported that further adjustments for population characteristic changes only amounted to a “modest” 1.25-fold increase in the risk for gestational diabetes in 2019 compared with 2005.

The researchers wrote that past research found gestational diabetes risks were stable in countries with unchanged screenings, while “in jurisdictions with variable screening practices, rates of diagnosis doubled or tripled over time, even when controlling for population changes.”

They highlighted one such study in the United States, which found age-adjusted gestational diabetes incidence increased from 4.8% in 2011 to 6.3% in 2019. However, they added the difference in incidence of gestational diabetes between the U.S. and British Columbia may reflect the American College of Obstetricians and Gynecologists’ guidelines’ criteria, “which have a higher diagnostic threshold than the current Canadian guideline.”

The researchers highlighted several limitations to the study, including the potential unmeasured confounding of patients’ family histories of diabetes or other underlying genetic factors. Additionally, 26% of patients were missing pre-pregnancy BMI.

Nethery and colleagues concluded that “although the generalizability of our findings to other jurisdictions is unknown, our study highlights the importance of having data on screening methods and completion to better understand the rising incidence of gestational diabetes observed elsewhere.”