Gestational diabetes has been reported to be on the rise, but a new study from British Columbia found that changes in screening practices explain much of the increase. The study is published in CMAJ (Canadian Medical Association Journal).

In Canada, the rate of gestational diabetes increased from 4% of deliveries in 2004 to 7% in 2014 across all racial and ethnic groups. The rise has been speculated to be because of older maternal age, less exercise and poor diet, but the reasons for the increase are poorly understood.

Researchers looked at data on more than 550 000 pregnancies in BC from 2005 to 2019 as well as the screening method and rates of screening completion. During the study period, diagnoses of gestational diabetes doubled, from 7.2% to 14.7%.

The authors found the increase was largely due to changes in gestational diabetes screening practices, from a 2-step screening process to a more sensitive 1-step screening process. When they adjusted for the increase in screen completion, changes in screening methods and population factors, diagnoses of gestational diabetes increased by less than one-quarter across the 15-year study period.

“Despite concerns that a higher proportion of pregnant people with high BMIs, older maternal age or obstetric risk factors were leading to higher rates of gestational diabetes, these were not important contributors to the yearly increase in gestational diabetes in BC,” says Dr. Elizabeth Nethery, School of Population and Public Health, University of British Columbia, with coauthors.

A diagnosis of gestational diabetes affects both the patient and the health system, requiring lifestyle changes, additional health care appointments and monitoring during and after pregnancy. In 2017, BC had the highest provincial rate of gestational diabetes at 13.9%, compared with 9.0% across Canada.

“[O]ur study highlights the importance of having data on screening methods and completion to better understand the rising incidence of gestational diabetes observed elsewhere,” the authors conclude.

“We need to look at gestational diabetes policies in BC, because screening changes alone are driving the substantial increase in diagnosis in our province. We need to make sure that any increase in diagnosis is truly beneficial to both patients and the health care system,” says Dr. Nethery, lead author of the study.

“The effect of changing screening practices and demographics on the incidence of gestational diabetes in British Columbia, 2005–2019” is published March 20, 2023.

Research: https://www.cmaj.ca/lookup/doi/10.1503/cmaj.221404