The effects of COVID-19 on placental morphology

Abstract

The impact of the COVID-19 infection, caused by Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), during the pandemic has been considerably more severe in pregnant women than non-pregnant women. Therefore, a review detailing the morphological alterations and physiological changes associated with COVID-19 during pregnancy and the effect that these changes have on the feto-placental unit is of high priority. This knowledge is crucial for these mothers, their babies and clinicians to ensure a healthy life post-pandemic. Hence, we review the placental morphological changes due to COVID-19 to enhance the general understanding of how pregnant mothers, their placentas and unborn children may have been affected by this pandemic. Based on current literature, we deduced that COVID-19 pregnancies were oxygen deficient, which could further result in other pregnancy-related complications like preeclampsia and IUGR. Therefore, we present an up-to-date review of the COVID-19 pathophysiological implications on the placenta, covering the function of the placenta in COVID-19, the effects of this virus on the placenta, its functions and its link to other gestational complications. Furthermore, we highlight the possible effects of COVID-19 therapeutic interventions on pregnant mothers and their unborn children. Based on the literature, we strongly suggest that consistent surveillance for the mothers and infants from COVID-19 pregnancies be prioritised in the future. Though the pandemic is now in the past, its effects are long-term, necessitating the monitoring of clinical manifestations in the near future.

Keywords: COVID-19; Morphology; Pathology; Placenta; Pregnancy.

Fig. 1

Shows the schematic representation of the human chorionic villi highlighting the structure. The trophoblast differentiates into the extravillous trophoblast and villous. The villous is composed up of a monolayer of cytotrophoblastic cells from the floating villi (in the intervillous space) which are still attached the villous basement membrane. When these cells differentiate and proliferate, they form the external covering of the villus, the syncytiocytotrophoblast layer. Adapted from Evain-Brion and Malassiné [22].

Fig. 2

Shows sections of placental samples that have been affected by SARS-CoV-2. Image 1 shows serially sectioned placenta from a case showing appearance of SARS-CoV-2 placentitis. Microscopic examination showed massive perivillous fibrin deposition, chronic histiocytic intervillositis, and trophoblast necrosis. The extent of pathology resulting from these destructive lesions was greater than 90% and led to placental insufficiency and stillbirth. Image 2 shows gross pathological appearance of massive perivillous fibrin deposition that occurred with SARS-CoV-2 placentitis from a stillborn foetus. Intervillous thrombohematomas can be seen. Image 3 shows sectioned placental specimen from a case illustrating SARS-CoV-2 placentitis. There was 70% involvement of placental tissue with this destructive process [Adapted from Schwartz et al. (2022)].

Fig. 3

A representative schematic diagram illustrated the maternal and foetal antibodies found after COVID-19 infection and vaccination [108].