Abstract
The current coronavirus disease 2019 (COVID-19) pandemic, caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has inflicted a serious health crisis globally. This virus is associated with a spectrum of respiratory illness ranging from asymptomatic, mild to severe pneumonia, and acute respiratory distress syndrome. Accumulating evidence supports that COVID-19 is not merely a respiratory illness per se, but potentially affects other organ systems including the placenta. SARS-CoV-2 gains access to human cells via angiotensin-converting enzyme 2 (ACE-2). The abundance of ACE-2 on the placental cell surface, especially the syncytiotrophoblasts, could potentially contribute to vertical transplacental transmission to the fetus following maternal COVID-19 infection. Intriguingly, despite the placentas being tested positive for SARS-CoV-2, there are very few newborns that manifest virus-induced diseases. The protective effects of the placental barrier to viral infection, limiting the spread of the virus to newborn infants, remain a mystery. The detrimental role of COVID-19 in pregnancies is largely debatable, although COVID-19 maternal infection has been implicated in unfavorable pregnancy outcomes. In this review, we summarize the pathological features manifested in placenta due to COVID-19 maternal infection that have been previously reported, and relate them to the possible disease manifestation. The potential mechanistic pathways associated with transplacental viral transmission and adverse pregnancy outcomes are also discussed.
Highlights
The 2019 coronavirus disease (COVID-19), a novel zoonotic disease [1], was first discovered in late December 2019 following an outbreak of severe pneumonia of unknown etiology in Wuhan, Hubei Province, China
Gajbhiye et al (2020) observed that only 24 (8%) out of 313 neonates born to mothers with COVID-19 tested positive for Severe Acute Respiratory Syndrome (SARS)-CoV-2 [8], which raises an important question on the success rate of transplacental viral infection to the fetus
We reviewed all articles with reports on placental pathology in pregnant women tested positive for SARS-CoV-2 that were published between 1 January 2020 to 10 October 2020 (n = 29) [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44]
Summary
The 2019 coronavirus disease (COVID-19), a novel zoonotic disease [1], was first discovered in late December 2019 following an outbreak of severe pneumonia of unknown etiology in Wuhan, Hubei Province, China. The etiological agent was successfully isolated and identified as a previously unknown beta-coronavirus, which was provisionally coined as 2019 novel coronavirus (2019-nCoV) [2] It was later officially designated as Severe Acute Respiratory Syndrome Virus 2 (SARS-CoV-2) on the ground of phylogenetic analysis by the International Committee on Taxonomy of Viruses [3]. Gajbhiye et al (2020) observed that only 24 (8%) out of 313 neonates born to mothers with COVID-19 tested positive for SARS-CoV-2 [8], which raises an important question on the success rate of transplacental viral infection (intrauterine transmission) to the fetus. The innate immune system, structural barrier, as well as the interaction between decidual immune cells and the invading fetal extravillous trophoblasts may play a role in the placental protective mechanisms against SARS-CoV-2 viral invasion.
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