Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.

Introduction: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during pregnancy is associated with an increased risk of preterm birth (PTB). The aim of the study was to investigate the effect of timing of SARS-CoV-2 infection during pregnancy on PTB risk and whether the risk is related to the interval from infection onset. We also studied whether the association is driven primarily by spontaneous or iatrogenic PTB, as well as to what extent disease severity, viral variant, background characteristics, and vaccination status affect the risk for PTB. Material and methods: This is a Swedish population-based register study including all singleton pregnancies registered in the Swedish Pregnancy Register with estimated date of birth between March 1, 2020 and May 31, 2022 ( Results: There was a significant ( Conclusions: Pregnant women are at particularly high risk of PTB within 14 days after a SARS-CoV-2 infection, and should be counselled on PTB symptoms to ensure that they seek medical care without delay. The increased PTB risk is partly mitigated by vaccination against SARS-CoV-2.