ABSTRACT
Background: Placental pathology in pregnant women infected by SARS-CoV-2 has generated many reports with non-specific or contradictory results. The objective is to identify histological and molecular findings of infected placentas and its impact on the course of pregnancy. Design: Placentas from 279 women infected with SARS-CoV-2 during pregnancy were reviewed, 137 of them with active infection within 10 days prior to delivery and 142 with past infection beyond this period. Four fetal autopsies were submitted for pathological study. Placental and fetal infection was investigated by immunohistochemistry (IHC) in 279 cases, RT-PCR in 27 cases and in situ hybridization (ISH) in 5 cases. Significance of association between qualitative variables was tested by Fisher's exact test. Results: SARS-CoV-2 infection of placental tissues was demonstrated in 16/279 (5,7%) by IHQ (granular cytoplasmic villous trophoblast staining) and confirmed by ISH and RT-PCR (carried on 5 IHQ positive cases). All these 16 infected placentas showed diffuse (6/16) or focal (10/16) Trophoblast Damage (DTD/FTD) characterized by trophoblast necrosis with preserved villous stroma, collapse of the intervillous space, intervillous fibrinoid deposits, and variable polymorphous inflammatory infiltrates. Cases with DTD (>80% of the parenchyma affected) resulted in 5 stillbirth and 1 premature alive baby (27w) born after induction of labor for pathologic fetal non-stress test. In 4/5 deaths an autopsy was performed and infection of fetal tissues was not demonstrated by IHQ. The cases with FTD (<35% of the parenchyma affected) hadn't negative impact on the fetus. Correlation between placental infection and DTD/FTD had statistical significance (p<0,001). 15/16 placentas belonged to the group of pregnant women with active infection within 10 days prior delivery. Correlation between DTD/FTD and maternal active infection had statistical significance (p<0,002). Conclusions: Placentas infected by SARS-CoV2 has a characteristic histological pattern that we have defined as DTD or FTD, characterized by a predominant villous trophoblast necrosis, intervillous space collapse and variable degrees of mixed inflammation and intervillous fibrinoid deposition. DTD/FTD is an infrequent lesion observed in 5,7% of pregnant women affected by COVID-19 in our series. DTD can be the cause of fetal death due to placental insufficiency. In this study, vertical transmission of the virus to the fetus has not been demonstrated.