Severity of SARS-CoV-2 infection in pregnant women and their neonates during the Omicron period compared to the pre-Omicron period: A retrospective cohort study

Aim: To compare the clinical outcomes among women diagnosed with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy, and their neonates, during the period when the Omicron variant predominated in Japan with those of the pre-Omicron variant period.Methods: We conducted a retrospective single-center cohort study between August 1, 2020, and June 30, 2022. The cohort was divided into pre-Omicron group (August 1, 2020 to November 30, 2021) and Omicron group (December 1, 2021 to June 30, 2022). The primary outcome was maternal intensive care unit (ICU) admission during the perinatal period. The secondary outcomes were maternal oxygen administration before and after delivery, preterm birth (PTB), and low birth weight (LBW).Results: During the study period, 81 pregnant women were admitted to the hospital with SARS-CoV-2 infection (pre-Omicron period, n = 28; Omicron period, n = 53). SARS-CoV-2 infection during the Omicron period was associated with lower risk of maternal ICU admission (adjusted-odds ratio [aOR]: 0.10, 95% confidence interval [CI]: 0.01-1.23, p = 0.072), oxygen administration via a nasal cannula or mask (aOR: 0.18, 95% CI: 0.03-0.96, p = 0.045), PTB (aOR: 0.15, 95% CI: 0.04-0.51, p = 0.002), and LBW (aOR: 0.13, 95% CI: 0.03-0.55, p = 0.005).Conclusion: Among pregnant women, SARS-CoV-2 infection during the Omicron period was associated with reduced risk of maternal ICU admission, requiring supplemental oxygen, PTB, and LBW. This can be attributable to lower virulence of the Omicron variant and higher vaccination coverage during the Omicron period.