Placental SARS-CoV-2 infection and its implications for increased risk of adverse pregnancy outcomes.

INTRODUCTION: Pregnant women are at increased risk of COVID-19. This could be explained through the prism of physiologic and immunologic changes in pregnancy. In addition, certain immunological reactions originate in the placenta in response to viral infections.

OBJECTIVE: This study aimed to investigate whether SARS-CoV-2 can infect the human placenta and discuss its implications in the pathogenesis of adverse pregnancy outcomes.

STUDY DESIGN: We conducted a retrospective cohort study in which we collected placental specimens from pregnant women who had a laboratory-confirmed SARS-CoV-2 infection. We performed RNA in situ hybridization (RNA-ISH) assay on formalin-fixed paraffin-embedded (FFPE) tissues to establish the in vivo evidence for placental infectivity by this corona virus. In addition, we infected trophoblast isolated from uninfected term human placenta with SARS-CoV-2 variants to further provide in vitro evidence for such an infectivity.

RESULTS: There was a total of 21 cases enrolled, which included five cases of spontaneous preterm birth (SPTB) and two intrauterine fetal demises (IUFDs). Positive staining of positive-sense strand (PSS) of SARS-CoV-2 virions was detected in 15 placentas including four SPTB and both IUFDs. In vitro infection assay demonstrated that SARS-CoV-2 virions were highly capable of infecting both cytotrophoblast and syncytiotrophoblast.

CONCLUSION: This study implies that placental SARS-CoV-2 infection may be associated with an increased risk of adverse obstetrical outcomes.