Systematic review and synthesis of stillbirths and late miscarriages following SARS-CoV-2 infections

OBJECTIVE: This study aimed to describe the characteristics of fetal demise after SARS-CoV-2 infections and clarify whether it is associated with clinical severity, placental lesions, or malformations or due to actual fetal infections. DATA SOURCES: PubMed and Web of Science databases were searched between December 1, 2019, and April 30, 2022. STUDY ELIGIBILITY CRITERIA: Cohort, cross-sectional, and case-control studies and case series or case reports describing stillbirths or late miscarriages (ie, pregnancy loss occurring between 14 and 22 weeks of gestation, before and after the onset of labor) from mothers with SARS-CoV-2 infection during pregnancy (demonstrated by at least 1 positive real-time reverse transcription-polymerase chain reaction from nasopharyngeal swabs and/or SARS-CoV-2 placental infection). No language restriction was applied; cases with other causes possibly explaining the fetal demise were excluded. METHODS: The Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Meta-analysis Of Observational Studies in Epidemiology guidelines were followed. The quality of the case series and case reports was evaluated using the specific Mayo Clinic Evidence-Based Practice Center tool. Maternal and clinical fetal data and placental and fetal virology and histology findings were collected. Data were summarized with descriptive statistics using the World Health Organization criteria to classify disease severity and fetal-neonatal infections. RESULTS: Data from 184 mothers and 190 fetuses were analyzed. No clear link to maternal clinical severity or fetal malformation was evident. Approximately 78% of fetal demise cases occurred during the second and third trimesters of pregnancy, approximately 6 to 13 days after the diagnosis of SARS-CoV-2 infection or the onset of symptoms. Most placentas (88%) were positive for SARS-CoV-2 or presented the histologic features of placentitis (massive fibrin deposition and chronic intervillositis) previously observed in transplacentally transmitted infections (85%–91%). Of note, 11 fetuses (5.8%) had a confirmed in utero transmitted SARS-CoV-2 infection, and 114 fetuses (60%) had a possible in utero transmitted SARS-CoV-2 infection. CONCLUSION: The synthesis of available data showed that fetal demise generally occurs a few days after the infection with histologic placental inflammatory lesions associated with transplacental SARS-CoV-2 transmission and eventually causing placental insufficiency.