Perinatal & Pediatric
Changes in gestational diabetes subtypes following a screening change in British Columbia, Canada: an interrupted time series analysis Elizabeth Nethery* Elizabeth Nethery Jennifer Hutcheon Julie Lee Patricia Janssen Laura Schummers
Background: In October 2010, regional guidelines for gestational diabetes mellitus (GDM) screening changed to use a lower diagnostic threshold for GDM. The new approach diagnosed GDM in pregnant individuals at lower hyperglycemia levels, which nearly doubled the incidence of GDM. It is unknown, however, whether the additional diagnoses were less severe GDM cases (“diet-controlled GDM”, treated through lifestyle changes) or more severe cases (“medication-dependent GDM”). We examined the effect of a screening guideline change on GDM subtypes.
Methods: We used a population-based linked cohort of all singleton pregnancies >28 weeks gestational age in 2008-2019, with GDM screening records. We identified GDM cases based on international classification of diseases coding on the delivery admission record and medication-dependent GDM based on one or more outpatient prescription records for glucose control medications during pregnancy. We used an interrupted time series design using linear regression to estimate changes in GDM types (medication-dependent and diet-controlled) following the policy change. We estimated risk ratios comparing the observed incidence of each GDM type with the expected incidence of each type in the post-policy period, controlling for underlying time trends.
Results: Among 472,595 singleton pregnancies, 7.9% were diagnosed with GDM during the pre-2010 period and 12.1% in the 2011-2019 period. The incidence of diet-controlled GDM increased from 6.2% pre-2010 to 8.9% post-change. From our interrupted time series models (Fig 1), we found a 1.33 (95% CI: 1.26, 1.41) relative risk increase (level change) in diet-controlled GDM. We found no change in the level or trend for medication-dependent GDM (level change: RR 0.94 [95% CI: 0.84 to 1.05]).
Conclusion: A change in GDM screening policy resulted in a 33% increase in the incidence of less severe diet-controlled GDM, but had no impact on incidence of more severe, medication-dependent GDM.
