Infection with SARS-CoV-2 during pregnancy and risk of stillbirth: a Scandinavian registry study.

Background: A few studies indicate that women infected with SARS-CoV-2 during pregnancy might have an increased risk of stillbirth. Our aim was to investigate the risk of stillbirth according to infection with SARS-CoV-2 during pregnancy also taking the variant into account. Methods: We conducted a register-based study using the Swedish, Danish and Norwegian birth registries. A total of 389 949 births (1013 stillbirths) after 22 completed gestational weeks between 1 May 2020 and end of follow-up (27 January 2022 for Sweden and Norway; 31 December 2021 for Denmark). We estimated the risk of stillbirth following SARS-CoV-2 infection after 22 completed gestational weeks using Cox regression for each country, and combined the results using a random-effects meta-analysis. Results: SARS-CoV-2 infection after 22 completed gestational weeks was associated with an increased risk of stillbirth (adjusted HR 2.40; 95% CI 1.22 to 4.71). The risk was highest during the first weeks following infection, with an adjusted HR of 5.48 (95% CI 3.11 to 9.63) during the first 2 weeks, 4.38 (95% CI 2.41 to 7.98) during the first 4 weeks, and 3.71 (95% CI 1.81 to 7.59) during the first 6 weeks. Furthermore, the risk was greatest among women infected during the Delta-dominated period (adjusted HR 8.23; 95% CI 3.65 to 18.59), and more modest among women infected during the Index (adjusted HR 3.66; 95% CI 1.89 to 7.06) and Alpha (adjusted HR 2.73; 95% CI 1.13 to 6.59) dominated periods. Conclusions: We found an increased risk of stillbirth among women who were infected with SARS-CoV-2 after 22 gestational weeks, with the greatest risk during the Delta-dominated period.