Increased incidence of gestational diabetes attributed to increased screening sensitivity in Canada

1. In this retrospective cohort study, the observed increase in the incidence of gestational diabetes was attributable to changes in screening practices rather than changing population factors in British Colombia, Canada.

Evidence Rating Level: 2 (Good)

Rates of gestational diabetes (GDM) are rising worldwide. Some suggest that population factors such as decreased physical activity and poor diet contribute to this observed increase in incidence. Alternatively, it is also theorized that these changes may be attributed to the increased sensitivity of screening arising from guideline changes in recent years. This retrospective cohort study sought to further investigate this, and examined 551 457 pregnancies, identified from the population-based BC Perinatal Data Registry, that underwent GDM screening between July 2004 and June 2019, to determine the extent to which changes in screening completion, screening method, and population-level characteristics contribute to the rise in gestational diabetes in BC, Canada. The rate of gestational diabetes increased from 7.2% of pregnancies in 2005 to 14.7% in 2019, representing a 2.04 (95% CI 1.94–2.13) increase in the risk of GDM. Screening completion rates, the use of 1-step screening, and population characteristics such as pre-pregnancy BMI, maternal age, and risk factors for poor obstetric outcomes also increased throughout the study period. After adjusting for the increase in screening completion, the risk of GDM in 2019 was attenuated to a 1.89-fold (95% CI 1.81–1.98) increase. After accounting for the screening method, the risk of GDM was attenuated to a 1.34-fold (95% CI 1.28–1.40) increase. Finally, adjustment for changes in population characteristics had a minor impact on the increased risk of GDM in 2019 compared with 2005 (1.25, 95% CI 1.19–1.31). These results suggest that changes in screening methods explained the majority of the increase in GDM from 2005 to 2019 in BC, Canada while changing population factors were not an important contributor. Therefore, instead of a true change in GDM incidence, new screening practices simply diagnose more cases of GDM. It is still uncertain whether the long-term benefits of decreases in cardiometabolic diseases or metabolic effects in GDM-identified offspring justify the drawbacks of an increased diagnostic burden.

Click to read the study in CMAJ

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