Association Between COVID-19 Pandemic Phases and the Risk of Maternal Intensive Care Unit Admission: A Retrospective Analysis of 215,363 Victorian Hospital Admissions.

Abstract

Background: There are no published Australian population-based data on serious COVID-19-associated maternal morbidity before and after widespread vaccination.

Aims: To compare COVID-19 infection rates, intensive care unit (ICU) admissions, and length of stay in hospitalised pregnant patients before and after achieving 70% state-wide maternal COVID-19 vaccination coverage.

Material and methods: Population-based retrospective cohort study involving all hospital-admitted episodes for pregnant patients over 15-years-old with COVID-19 in Victoria from 1 March 2020 to 31 March 2022. Phase 1 was defined as March 2020-October 2021 when maternal vaccination coverage < 70%; Phase 2 was defined as November 2021-March 2022 when maternal vaccination coverage ≥ 70%. Primary outcomes include COVID-19 rates, ICU admission rates, and length of stay. A p-value of < 0.05 was considered statistically significant.

Results: We analysed 215,363 hospital admissions, among which 2,128 (0.99%) had COVID-19. The percentage of admitted pregnant patients with COVID-19 was higher in Phase 2 than Phase 1 (3.27% vs. 0.41% respectively, p < 0.001). However, Phase 2 was associated with lower maternal ICU admission rates (2.02% vs. 5.39%, p < 0.001) and lower median length of stay (2.19 vs. 3.11 days, p < 0.001) compared with Phase 1. The risk of COVID-19 was significantly lower in socioeconomically advantaged pregnant patients (aRR = 0.83 [95% CI, 0.76-0.90], p < 0.001) and pregnant patients ≥ 30-years-old (aRR = 0.81 [95% CI, 0.74-0.88], p < 0.001).

Conclusions: Maternal ICU admission risk and length of stay were significantly lower among pregnant patients with COVID-19 during Phase 2, which is likely due to the combined effects of high maternal COVID-19 vaccination coverage and changes in SARS-CoV-2 variants.