The effect of changing screening practices and demographics on the incidence of gestational diabetes in British Columbia, 2005–2019

Abstract

Background: Rates of gestational diabetes are reported to be increasing in many jurisdictions, but the reasons for this are poorly understood. We sought to evaluate the relative contribution of screening practices for gestational diabetes (including completion and methods of screening) and population characteristics to risk of gestational diabetes in British Columbia, Canada, from 2005 to 2019. Methods:We used a population-based cohort from a provincial registry of perinatal data, linked to laboratory billing records. We used data on screening completion, screening method (1-step 75-g glucose test or 2-step approach of 50-g glucose screening test, followed by a diagnostic test for patients who screen positive) and demographic risk factors. We modelled predicted annual risk for gestational diabetes, sequentially adjusted for screening completion, screening method and risk factors. Results:We included 551 457 pregnancies in the study cohort. The incidence of gestational diabetes more than doub led over the study period, from 7.2% in 2005 to 14.7% in 2019. Screening completion increased from 87.2% in 2005 to 95.5% in 2019. Use of 1-step screening methods increased from 0.0% in 2005 to 39.5% in 2019 among those who were screened. Unadjusted models estimated a 2.04 (95% confidence interval [CI] 1.94-2.13) increased risk of gestational diabetes in 2019 (v. 2005). This increase was 1.89 (95% CI 1.81-1.98) after accounting for the rise in screening completion and 1.34 (95% CI 1.28-1.40) after accounting for changes in screening methods. Further accounting for demographic risk factors (e.g., age, body mass index, prenatal care) had a small impact (increase of 1.25, 95% CI 1.19-1.31).Interpretation: Most of the observed increase in the incidence of gestational diabetes was attributable to changes in screening practices (primarily changes in screening methods) rather than changing population factors. Our findings highlight the importance of understanding variation in screening practices when monitoring incidence rates for gestational diabetes.

A call to reconsider the new diagnostic criteria for gestational diabetes mellitus

“… 6 We estimated that about 57% of people with gestational diabetes according to the new diagnostic practices, may be overdiagnosed. 6 Applying that estimate to data in the current report, more than 7800 pregnant people may have been overdiagnosed in 2019 alone (57% of 13 743, using the 1-step test in 2019, shown in Table 1 of the article by Nethery and colleagues 1 ).…”

“…We read the article by Nethery and colleagues 1 with great interest, having noted a similar dramatic increase in the incidence of gestational diabetes in Australia, coincident with widespread adoption of the 1-step test using the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criteria. Although the authors did not examine clinical or health system effects from the change in diagnostic practice, they noted that, “Health system costs may increase, with a need for more endocrinologists, diabetes nurse educators or dietitians; additional sonograms; or more intensive monitoring during labour, delivery and the postpartum period.”…”