Table 2.

Clinicopathologic features in placentas from SARS-CoV-2 positive mothers with and without fetal demise [^{6,12,13,20,22,47,49,50}, present cases]

• Overall, placental infection by SARS-CoV-2 is seen in < 10% of SARS-CoV-2-positive mothers,
• Morphologic pattern of placental infection include:
Chronic histiocytic predominant intervillositis (mostly seen in cases with live born infants),
Trophoblastic necrosis,
Intervillous space collaps and
Variable amount of perivillous fibrin deposition,
• Placentas from SARS-CoV-2-positive mothers without fetal distress may represent no or only little intervillous fibrin deposits and/or histiocytic intervillositis,
• In pregnancies affected by fetal distress, intrauterine growth restriction or even intrauterine death, increased intervillous fibrin deposits are present, mostly in placentas from the second trimester,
• Reported increased perivillous fibrin deposition is very rarely associated with fetal growth restriction compared to intrauterine death, suggesting rapid onset of intervillous fibrin deposition resulting in acute intervillous hypoxia
• Intervillous fibrin deposits represent a multifactorial pathogenetic process caused by a combination of maternal hypercoagulation process resulting in intervillous hypoxic conditions and perhaps a direct damage of the trophoblastic cells on the villous surface by cytokine/microparticle storm and cytokine activation
•may be caused by increased trophoblastic ACE-2-receptor expression, 1st and 2nd trimester represent the most vulnerable time period for placental SARS-CoV-2 infection,
• Although the detection of SARS-CoV-2 within the placental tissue has been reported using in situ-techniques or immunohistochemistry, that feature is not as common in SARS-CoV-2-positive mothers,
• Adverse clinical outcome may also be seen in asymptomatic mothers or those with subclinical COVID-19