Clinical Outcomes Following a Change in Gestational Diabetes Mellitus Diagnostic Criteria Due to the COVID-19 Pandemic: A Case-Control Study

Background: Due to COVID-19, many centres adopted a change to the diagnosis of GDM. Methods: A case-control study of antenatal patients between 1 April and 30 June in 2019 and 2020 looking at detection rates of GDM, use of medication, obstetric, and fetal outcomes. Results: During COVID-19, the rate of positive GDM tests approximately halved (20% (42/210) in 2020 vs. 42.2% (92/218) in 2019, (p < 0.01)) with higher rates of requirement for insulin at diagnosis (21.4% (2020) vs. 2.2% (2019); p < 0.01), and at term (31% (2020) vs. 5.4% (2019); p < 0.01). and metformin at diagnosis (4.8% (2020) vs. 1.1% (2019); p < 0.01), and at term (14.3% (2020) vs. 7.6% (2019) p < 0.01), with no differences in birth outcomes. Conclusions: There was likely an underdiagnosis of GDM while women at a higher risk of hyperglycaemia were correctly identified. The GTT should be maintained as the gold-standard test where possible, with provisions made for social distancing during testing if required.