An Observational Comparison of Gestational Diabetes Mellitus Prevalence and Pregnancy Outcomes Before and During COVID-19 in the Australian Capital Territory, 2018–2021

Background: In the Australian Capital Territory (ACT) during the Coronavirus disease 2019 (COVID-19) pandemic, gestational diabetes mellitus (GDM) testing using the World Health Organization’s (WHO) oral glucose tolerance test (OGTT) was replaced with temporary guidelines comprising two phases: the red phase, with fasting glucose ≥5.1 mmol/L (diagnosed) and <5.1 mmol/L (excluded); and the subsequent amber phase of screening with fasting ≥5.1 mmol/L (diagnosed), <4.7 mmol/L (excluded) and 4.7–5.0 mmol/L, requiring completion of an OGTT. Aims: Our aim was to determine whether there were differences in GDM prevalence, maternal characteristics or infant outcomes during the COVID-19 pandemic period, in association with implementation of the temporary guidelines. Methods: We performed a before–during observational analysis of 9686 singleton births between April 2018 and December 2019 (pre-COVID-19, group 1, n = 4879) or April 2020 and December 2021 (COVID-19, group 2, n = 4807). Group 2 comprised subgroups 2a (1 April–2 November 2020, n = 1845) and 2b (3 November 2020–31 December 2021, n = 2962). The GDM testing date was estimated at 26 weeks of gestation and used for group assignment. For GDM diagnosis, group 1 applied the WHO OGTT, and group 2 applied the temporary guidelines (2a the red phase; 2b the amber phase). Associations were tested using chi-square tests, pairwise z-tests and logistic regression. Results: Compared to group 1, GDM prevalence significantly decreased in subgroup 2a (26.7% vs. 21.7%) and significantly increased in subgroup 2b (26.7% vs. 31.7%) (all: p < 0.001). For non-GDM pregnancies, there were no significant associations nor significant differences for infant outcomes when group 1 was compared to subgroups 2a and 2b. Subgroup 2a pregnancies with insulin-requiring GDM, compared to Group 1 counterparts, had significantly higher odds of infants with LGA (aOR = 1.73, 98.75% CI of 1.04–2.89, p = 0.008) and macrosomia (aOR = 2.05, 98.75% CI of 1.09–3.86, p = 0.004). Conclusions: The COVID-19 period and the temporary guidelines were associated with changes in GDM prevalence, which differed by phase. No increase was observed in adverse infant outcomes in non-GDM pregnancies. GDM pregnancies in the red phase had worse infant outcomes, which may have been due to enrichment of this group with elevated fasting GDM.