Abstract
Severe acute respiratory syndrome coronavirus 2 has been causing the pandemic of coronavirus disease 2019 (COVID-19) that has so far resulted in over 450 million infections and six million deaths. This respiratory virus uses angiotensin-converting enzyme 2 as a receptor to enter host cells and affects various tissues in addition to the lungs. The present study reports that the placental arteries of women who gave birth to live full-term newborns while developing COVID-19 during pregnancy exhibit severe vascular wall thickening and the occlusion of the vascular lumen. A morphometric analysis of the placental arteries stained with hematoxylin and eosin suggests a 2-fold increase in wall thickness and a 5-fold decrease in the lumen area. Placental vascular remodeling was found to occur in all of SARS-CoV-2-positive mothers as defined by RT-PCR. Immunohistochemistry with α-smooth muscle actin and the Kv11.1 channel as well as Masson's trichrome staining showed that such placental vascular remodeling in COVID-19 is associated with smooth muscle proliferation and fibrosis. Placental vascular remodeling may represent a response mechanism to the clinical problems associated with childbirth in COVID-19 patients.