SARS‐CoV‐2 infection among hospitalised pregnant women and impact of different viral strains on COVID‐19 severity in Italy: a national prospective population‐based cohort study

Objective The primary aim of this article was to describe SARS‐CoV‐2 infection among pregnant women during the wild‐type and Alpha‐variant periods in Italy. The secondary aim was to compare the impact of the virus variants on the severity of maternal and perinatal outcomes. Design National population‐based prospective cohort study. Setting A total of 315 Italian maternity hospitals. Sample A cohort of 3306 women with SARS‐CoV‐2 infection confirmed within 7 days of hospital admission. Methods Cases were prospectively reported by trained clinicians for each participating maternity unit. Data were described by univariate and multivariate analyses. Main outcome measures COVID‐19 pneumonia, ventilatory support, intensive care unit (ICU) admission, mode of delivery, preterm birth, stillbirth, and maternal and neonatal mortality. Results We found that 64.3% of the cohort was asymptomatic, 12.8% developed COVID‐19 pneumonia and 3.3% required ventilatory support and/or ICU admission. Maternal age of 30–34 years (OR 1.43, 95% CI 1.09–1.87) and ≥35 years (OR 1.62, 95% CI 1.23–2.13), citizenship of countries with high migration pressure (OR 1.75, 95% CI 1.36–2.25), previous comorbidities (OR 1.49, 95% CI 1.13–1.98) and obesity (OR 1.72, 95% CI 1.29–2.27) were all associated with a higher occurrence of pneumonia. The preterm birth rate was 11.1%. In comparison with the pre‐pandemic period, stillbirths and maternal and neonatal deaths remained stable. The need for ventilatory support and/or ICU admission among women with pneumonia increased during the Alpha‐variant period compared with the wild‐type period (OR 3.24, 95% CI 1.99–5.28). Conclusions Our results are consistent with a low risk of severe COVID‐19 disease among pregnant women and with rare adverse perinatal outcomes. During the Alpha‐variant period there was a significant increase of severe COVID‐19 illness. Further research is needed to describe the impact of different SARS‐CoV‐2 viral strains on maternal and perinatal outcomes.
Tweetable abstract The rate of severe COVID‐19 disease increased during the Alpha‐variant period compared with the wild‐type period.