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The impact of SARS-CoV-2 infection on term placentae


1 Department of Pathology, KMCH Institute of Health Sciences and Research, Coimbatore, Tamil Nadu, India
2 Department of Obstetrics and Gynaecology, KMCH Institute of Health Sciences and Research, Coimbatore, Tamil Nadu, India

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Date of Submission03-Mar-2021
Date of Decision09-Nov-2021
Date of Acceptance12-Nov-2021
Date of Web Publication24-May-2022
 

   Abstract 


Background: Coronavirus 2019 infection (COVID 19) is an ongoing pandemic caused by pathogenic RNA viruses called severe acute respiratory syndrome coronavirus-2 (SARS-COV-2). It has affected people of all ages, with high morbidity and mortality among the elderly and immunocompromised population. Limited information is available on the effects of COVID-19 infection on pregnancy. Aim: To describe the histopathological changes in the placental tissue of SARS-CoV-2 infected term mothers with no comorbidities and to correlate with neonatal outcome. Materials and Methods: This observational study was conducted in the Department of Pathology, KMCH institute of health sciences and research, Coimbatore from May 1, 2020 to November 30, 2020 for 6 months. Placental tissues of all COVID-19-positive term mothers with no comorbidities were included in this study. Histopathological examination of placentae was carried out and clinical data of mothers and newborn babies were obtained from medical records. Results: Histopathological examination of 64 placental tissue of COVID-19 mothers showed predominantly the features of fetal vascular malperfusion like stem villi vasculature thrombus, villous congestion, and avascular villi. No significant correlation was obtained in comparison with parity and symptomatic status of the mothers. However, histopathological changes were more prominent among symptomatic patients. The newborn babies born to these mothers showed no adverse outcome. Conclusion: This study concluded that though COVID-19 infection in normal term pregnant women was associated with increased prevalence of features of fetal vascular malperfusion, there was no significant morbidity in the health status of both COVID-19 mothers and their neonates

Keywords: Fetal vascular malperfusion, severe acute respiratory syndrome coronavirus-2, term placentae


How to cite this URL:
Karthikeyan T M, Sundari A A, Veenaa N N, Shivapriya R, Prema N. The impact of SARS-CoV-2 infection on term placentae. Indian J Pathol Microbiol [Epub ahead of print] [cited 2022 Nov 27]. Available from: https://www.ijpmonline.org/preprintarticle.asp?id=345863





   Introduction Top


Coronavirus 2019 infection (COVID-19) is a highly contagious and pathogenic viral infection caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Infection originated initially in the Wuhan city of China and spread all over the world affecting nearly 90 million population and causing 2 million deaths. In India, 10 million cases were reported till December 2020 with around 152,000 deaths.[1]

Coronaviruses are large enveloped single-stranded RNA viruses belonging to the family Coronaviridae. There are seven coronavirus species that are known to infect humans and can cause a wide range of symptoms from mild flu to fatal pneumonia. The first coronavirus outbreak was caused by severe acute respiratory syndrome (SARS) in 2002 in China, which was highly infectious with case fatality rate accounting to 10%. SARS was followed by another novel coronavirus outbreak caused by Middle-East respiratory syndrome coronavirus (MERS-CoV) reported first in Saudi Arabia with a high case mortality rate of 35%. The ongoing pandemic caused by SARS-CoV-2 has its origin again from Wuhan, China.[2],[3]

All age groups were equally infected by the SARS-CoV-2 virus. Infectivity in elderly and immunocompromised people showed a poor clinical outcome.[4] Due to changes in the immune system and respiratory function, pregnant women were more vulnerable to coronavirus infection.

The virus is transmitted by respiratory droplets and aerosols. Once the virus enters the body, it attaches to the host cell receptor through its surface protein called spike protein (S protein) and enters the cell by membrane fusion or endocytosis, which is followed by replication and maturation of viral particles. Studies have proven that angiotensin-converting enzyme-2 (ACE-2) acts as an entry receptor for COVID-19 virus. ACE-2 is a type I transmembrane protein of 805 amino acids and is present in the tissues like the lung, kidney, gastrointestinal tract, and vascular endothelial cells. ACE-2 is also present in the cytotrophoblast and syncytiotrophoblastic layer of placental tissue.[5],[6],[7],[8]

COVID-19 infection produces limited immune response in 80% of cases, whereas the remaining 20% shows a cytokine storm caused by release of interleukins and interferons, which leads to an exaggerated immune response (like CD8-mediated tissue injury) or a hypercoagulable state resulting in widespread microthrombi formation. Since placental tissue is an interface between mother and fetus and expresses the ACE-2 receptors, it is expected to produce histopathological changes either due to direct tissue injury or due to microthrombi formation.[9]

Limited data are available on the prevalence of placental COVID-19 infection and their associated histomorphological changes. The present study attempts to describe the histopathological changes in the placental tissue of SARS-CoV-2-infected term mothers with no comorbidities and to correlate with perinatal outcomes.


   Materials and Methods Top


Patients/Placentae

The present study was an observational study and was conducted in the Department of Pathology from May 1, 2020 to November 30, 2020 for 6 months. During this period, all antenatal mothers attending Obstetrics and Gynecology department were routinely screened for COVID-19 infection via nasopharyngeal polymerase chain reaction (PCR). A total of 96 placentae of COVID-19-positive mothers was received. Placenta was transferred by trained staff in a leak-proof plastic container. Sixty-four cases were from normal mothers with no comorbidities. Placental tissue from all COVID-19-positive normal antenatal women with gestational age of more than 37 weeks sent to the department of pathology was included in this study. Placentas of mothers with medical and obstetric complications such as gestational diabetes, pregnancy-induced hypertension, oligohydramnios, coagulopathy, autoimmune disorders, and twin pregnancy were excluded from the study as they produce changes in histomorphology of placenta, which, in turn, interfere with the quality of data. Institutional ethical committee approval was obtained for this study. Clinical details of mothers and neonates regarding COVID-19 symptoms, birth weight, and APGAR score (Appearance, Pulse, Grimace Activity qnd Respiration) at the first and fifth minute of birth were retrieved from case records.

Tissue processing

The placentae of COVID-19-positive mothers satisfying selection criteria were sent in formalin fixative soon after delivery. As Darnell et al.[10] have mentioned that formalin can inactivate the SARS-CoV at 37°C or room temperature after 1 day, specimens were fixed in 10% neutral-buffered formalin for 3 days following which the histopathological examination was carried out. Personal protective measures like N95 masks, fluid-resistant double gloves, disposable plastic apron, protection goggles, and face shield were followed before handling the specimen. External surface of the specimen container was cleaned with 70% ethanol. Measurement of umbilical cord and placental disc was taken. The membranes and cord were trimmed off from the placenta in all cases and weighed on a weighing machine graduated in grams (g). They were sectioned at 5 mm intervals. Placental tissue was grossly examined. Sections were taken from umbilical cord, fetal membranes, chorionic plate, and placental parenchyma. Additional sections were taken from any apparent abnormalities. After grossing, the work surfaces were disinfected with 70% ethanol. The tissue blocks were routinely processed and paraffin-embedded, sectioned and stained with hematoxylin and eosin.

Standard definitions used in this study

Hypocoiling is defined as coils in umbilical cord occurring less than one per 10 cm and those with more than three coils per 10 cm are categorized as hypercoiling of umbilical cord.[11] Grossly, Infarct in placental parenchyma is considered pathological when it occupies more than 5% of placental parenchyma at nonperipheral location in term placenta.[11] Chorioamnionitis, which occurs as a result of maternal inflammatory response, is categorized into stage 1- infiltrate in subchorionic space; stage 2- infiltrate extending to fibrous chorion and amnion; and stage 3 as karyorrhexis, amniocyte necrosis, or basement membrane hypereosinophilia. Distal villous hypoplasia is defined as paucity of villi in relation to the surrounding stem villi and it should occupy lower one-third of total parenchymal thickness. Accelerated villous maturation denotes the presence of small hypermature villi for gestational age. Decidual arteriopathy is characterized by elements like fibrinoid necrosis, mural hypertrophy, incomplete spiral artery remodeling, and arterial thrombosis. Infarction is characterized by villous agglutination or collapse of the intervillous space with loss of distinct nuclear basophilia of the syncytium with “smudging” of nuclei.[12] Avascular villi is defined as total loss of villous capillaries and bland hyaline fibrosis of the villous stroma but with viable trophoblast.[12] Villous Stromal-Vascular Karyorrhexis is 3 or more foci of 2 to 4 terminal villi showing karyorrhexis of fetal cells (nucleated erythrocytes, leukocytes, endothelial cells, and/or stromal cells) with preservation of surrounding trophoblast.[11] Chorangiosis is defined as 10 or more capillaries in each of 10 villi in 10 fields inspected with a 10× objective in three different, noninfarcted areas of the placenta.[12]

Gross examination

Umbilical cord was examined for the presence of trivessel, true/pseudoknot, number of coils per 10 cm, handedness of coils, and the type of insertion. Condition of the membranes were assessed for color and opacity, amnion bands, amnion nodosum, and ruptured site was measured from the closest placental disc margins. Chorionic plate and placental parenchyma were examined for the presence of infarction, hematoma, and thrombus formation. Any grossly identified lesions were described by their location, number, and percentage of total parenchymal involvement.

Microscopic examination

Sections from placental tissues were assessed microscopically as per the guidelines of Amsterdam Placental Workshop Group Consensus. Sections taken from umbilical cord were looked for the presence of trivessels, any thrombus, or embryonic remnants. Membranes were screened for the presence of acute or chronic inflammatory infiltrate. Placental parenchyma was screened to identify any pathology in chorionic plate, villous architecture, and intervillous space. Features like avascular villi, occlusive thrombi, intramural fibrin deposition, and villous stromal vascular karyorrhexis were categorized under fetal thrombotic vasculopathy or fetal vascular malperfusion. Microscopic features like distal villous hypoplasia, accelerated villous maturation, villous congestion, infarcted villi, and decidual arteriopathy were categorized under maternal vascular malperfusion.[11]


   Observation and Results Top


This observational study was done in the placental tissue of 64 COVID-19-positive mothers (confirmed by nasopharyngeal swab RT-PCR methods) belonging to the age group of 20 to 36 years. A total of 34.4% of them were in the age group of 20 to 25 years, 50% between 26 and 30 years, and 15.6% were above 30 years of age. Pertaining to parity of mothers, 65.6% of women were primigravida. Most of the primigravida were in their 38th week of gestation constituting about 46.9%. A total of 82.8% of COVID-19-positive mothers included in the study were suffering from mild symptoms such as cough, myalgia, and fever for a week prior to delivery. All women were clinically stable and no oxygen support was required [Table 1].
Table 1: Clinical profile of COVID-19-positive mothers and newborn infants

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Neonates born to COVID-19 infected mothers were of normal birth weight (i.e., between 2.5 and 3.5 kg) accounting for around 89.1% and remaining 10.9% of babies belonged to low birth weight category (i.e., between 2 and 2.5 kg birth weight). All the neonates were screened for COVID-19 by real-time-PCR (RT-PCR) on day 1. Out of 64, two babies were tested positive. All the neonates were asymptomatic. Details about APGAR scores of all babies of COVID-19mothers showed that all (100%) neonates had a score of 8 and 9 at the end of the first and fifth minutes of birth. None of the neonates showed any symptoms and signs of COVID-19 infection and all were discharged within 3 days of life [Table 1].

Gross examination of placental tissue with attached membranes and umbilical cord showed that placental weight was adequate for gestational age in 90.4% of cases, large for gestational age in 8% of cases, and small for gestational age in 1.6% of cases. Marginal insertion, hypercoiling, and amnion bands were noted in 1.6% of cases in this study and were considered not significant. Recent placental infarct and areas of retroplacental hemorrhage were noted in 3.2% of placental tissue [Table 2].
Table 2: Gross findings of placentae of COVID-19-positive mothers

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Microscopic examination of placental tissue of 64 COVID-19-positive mothers showed predominantly the features of fetal vascular malperfusion like stem villus vasculature thrombus, villous congestion, and avascular villi. A total of 25% of mothers showed occlusive or nonocclusive thrombi in their stem, mature, intermediate, and terminal villous vasculature [Figure 1] and [Figure 2]. Avascular villi was observed in 26.6% of cases and 11.2% of cases showed villous congestion [Figure 3] and [Figure 4]. Additional findings such as chorangiosis, acute chorioamnionitis, and intervillous hemorrhage were noted [Figure 5] and [Figure 6]. Intervillous thrombus was noted in 1.6% of patients [Table 3].
Figure 1: Placental parenchyma showing fibrin thrombi with organization in stem villus vasculature (H&E, 40×)

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Figure 2: Placental parenchyma showing nonocclusive thrombi in stem villus vasculature (H&E, 40×)

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Figure 3: Placental parenchyma showing focus of avascular villi with lack of fetal capillaries and stroma showing hyalinization (H&E, 40×)

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Figure 4: Placental parenchyma showing villous congestion (H&E, 40×)

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Figure 5: Placental parenchyma showing focus of villi containing more than 10 fetal capillaries (H&E, 40×)

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Figure 6: Placental parenchyma showing intervillous hemorrhage and congestion (H&E, 40×)

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Table 3: Microscopic findings of placentae of COVID-19-positive mothers

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Correlation of histopathological findings with clinical profile of patients was done using SPSS software version 27.0. Prevalance of the features of fetal vascular malperfusion with parity and symptomatic status of the patients was analyzed using Chi-square test. Parity and symptomatic status of the patients showed no significant correlation with histopathological changes of placental tissue. Presence of fetal vascular malperfusion was noticed more frequently among symptomatic patients [Table 4] and [Table 5].
Table 4: Correlation of histopathological changes with parity of COVID-19-positive mothers

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Table 5: Correlation of histopathological changes with symptomatic status of COVID-19-positive mothers

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   Discussion Top


The present observational study analyzed the clinical characteristics, histopathological changes of placenta in 64 COVID-19-positive term pregnant women with no comorbidities. The most significant finding was an increase in the presence of fetal vascular malperfusion like stem vessel vascular thrombi (both nonocclusive and occlusive), villous congestion, and avascular villi. There was no statistical significance when correlated with the parity and symptomatic status of the antenatal mothers. However, nearly one-third of the symptomatic patients showed features of villous thrombi and avascular villi. This indicated that the histopathological changes were prominent in symptomatic patients than asymptomatic mothers.

Limited studies and case reports are available in this area. Case control study done by Debelenko et al.[13] among 75 COVID-19-positive patients at term showed no significant histopathological changes in the placental tissue except in a single case showing the features of intervillositis. Shanes et al.[14] described the features of maternal vascular malperfusion in 12 out of 15 cases in the second and third trimesters. Similar to this study, Bergen et al.[15] observed the features of fetal vascular malperfusion in 20 placental tissues of COVID-19-positive mothers.

Study done by Smithgall et al.[16] showed histopathological features like villous agglutination and subchorionic fibrin. Hecht et al.[17] observed no characteristic pathological changes in the placental tissue of 19 COVID-19 mothers. Patberg et al.[18] showed features of fetal vascular malformation in 20 patients similar to this study.

The limitations of the present study were the low number of patients, the symptomatic patients included in this study were with mild symptoms and they were diagnosed a week prior to delivery. The effect on maternal and fetus safety can be significantly analyzed if the study is carried out in placental tissues of a large number of patients with severe COVID-19 infection and in mothers who were exposed to COVID-19 infection in early or mid-trimester and continued the pregnancy till term. This aspect paves the way for future research.


   Conclusion Top


We analyzed sixty-four placentae of term COVID-19-positive mothers with no other comorbidities. There was no pathognomic finding. However, the cases showed increased prevalence of features of fetal vascular malperfusion that was more common among symptomatic patients. This suggests that the occurrence of fetal vascular malperfusion was due to viral infection-induced hypercoagulable state. Despite this change, neonatal well-being was not affected. This study concludes that COVID-19 infection in term mothers does not affect the newborn despite showing some histopathological changes in placental tissue. However, infection in early pregnancy may produce significant changes in placental histopathology and neonatal outcome warranting crucial antenatal surveillance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Patberg ET, Adams T, Rekawek P, Vahanian SA, Akerman M, Hernandez A, et al. Coronavirus disease 2019 infection and placental histopathology in women delivering at term [published correction appears in Am J Obstet Gynecol 2021]. Am J Obstet Gynecol 2021;224:382.e1-18.  Back to cited text no. 18
    

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Correspondence Address:
R Shivapriya,
Flat No 402, Icc Diya Apartment, Grg Chandra Gandhi Nagar, Peelamedu, Coimbatore, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_237_21



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