Assessing the Mother-to-infant Transmission Capabilities of COVID-19 Infection Among Pregnant Women in Ontario, Canada

Pregnant individuals with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection were more likely to experience greater disease severity and higher rates of hospitalization, intensive care unit (ICU) admission and death compared to their non-pregnant counterparts. Early pandemic data were limited to a few small case series and reports that failed to provide a clear understanding of the timing and likelihood of fetal/neonatal infection. Data now suggest that in utero, intrapartum and early postnatal transmission of SARS-CoV-2 to the fetus/neonate is rare (\<5%) and predominantly associated with third trimester infections and severe disease presentation. A living systematic review and meta-analysis of 144 cohort studies found that the rate neonates/fetuses testing positive for SARS-CoV-2 by RT-PCR, having anti-SARS-CoV-2 IgM antibodies or both was 1.94% (95%CI 1.31%, 2.66%). However, tests for SARS-CoV-2 and anti-SARS-CoV-2 antibodies were limited during the earliest stages of the pandemic and relatively few of the included studies provided sufficient data on the timing of fetal/neonatal exposure, and the type and timing of tests performed. Derivation of reliable risk estimates for perinatal transmission remains challenging due to significant heterogeneity across published studies regarding the types of tissues profiled, diagnostic methods used and availability of essential COVID-19 disease characteristics such as timing and severity of maternal infection. As variants of concern continue to emerge, more data are required to elucidate the circumstances in which SARS-CoV-2 infection is likely to be transmitted to the developing fetus/neonate. We sought to evaluate the rate of SARS-CoV-2 transmission from mother-to-neonate in a large multicenter cohort from Ontario and Quebec, Canada. To address early pandemic challenges in characterizing perinatal infections, a prospective cohort study was conducted across 14 sites in Ontario and Quebec, Canada. Pregnant individuals who had received a diagnosis of SARS-CoV-2 infection in pregnancy were eligible. Sample collection at delivery included maternal samples (nasopharyngeal/oropharyngeal, vaginal and anorectal swabs; blood; breastmilk), newborn samples (nasopharyngeal swabs, cord blood, amniotic fluid), and placental samples (sub-amniotic swab, placental biopsies). Swab, amniotic fluid, placenta and breastmilk samples were analyzed for SARS-CoV-2 RNA by RT-qPCR. Blood, breastmilk and amniotic fluid were assessed for anti-SARS-CoV-2 spike (S), receptor binding domain (RBD) and nucleocapsid (N) IgG, IgM and IgA.