Association of SARS-CoV-2 Infection during pregnancy with placental weight and histopathologic lesions

Introduction: The reported gross and histopathologic changes in the placenta associated with SARS-CoV-2 infection are heterogeneous. We sought to summarize placental histopathologic findings from pregnancies affected by SARS-CoV-2 infection according to timing of infection and symptom severity.

Methods: We conducted a retrospective cohort study of patients with SARS-CoV-2 infection during pregnancy who had deliveries at Mayo Clinic, Rochester, Minnesota, from April 2020 through June 2021. Placental histopathologic findings and clinical characteristics were compared for infections before vs after 28 weeks' gestation and according to COVID-19 symptom severity.

Results: We analyzed 93 cases of SARS-CoV-2 infection during pregnancy, with 51 % of infections occurring before 28 weeks' gestation. Infections were categorized as asymptomatic (14 %), mild (77 %), moderate (6 %), and severe (3 %) according to World Health Organization criteria. An increased risk of small placental weight (<10th percentile) was associated with maternal infection at all gestational ages (30 %, P < .001). Histopathologic lesions consistent with maternal vascular malperfusion occurred more often for infections before than after 28 weeks' gestation (18/46, 38 % vs 9/47, 19 %; P = .047) and did not differ in frequency according to symptom severity. Inflammatory changes were present in 50 % of the placentas examined but did not differ by group, except that acute fetal vasculitis occurred more frequently after asymptomatic vs symptomatic maternal infection (23 % vs 5 %; risk ratio, 4.62; 95 % CI, 1.16-18.30).

Discussion: COVID-19 at any gestational age or severity increases the risk of small placental weight and the presence of placental inflammatory lesions.