Assessment of Maternal and Neonatal Cord Blood SARS-CoV-2 Antibodies and Placental Transfer Ratios

PURPOSE OF THE STUDY: To assess the association between maternal and neonatal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody concentrations. STUDY POPULATION: Mother and newborn dyads (n = 1471) from 1714 parturient women at a single, urban, hospital center in Pennsylvania from April 9, 2020 to August 8, 2020. METHODS: Pregnant women who delivered at Pennsylvania Hospital were screened for SARS-CoV-2 by nasopharyngeal polymerase chain reaction (PCR) upon admission, SARS-CoV-2 exposure, and development of coronavirus disease 2019 (COVID-19) symptoms. Residual maternal and cord blood sera routinely collected at delivery were used for SARS-CoV-2 spike protein antibody measurement using a validated enzyme-linked immunosorbent assay. Antibody (IgG, IgM) concentrations and transplacental transfer ratios were analyzed along with demographic and clinical data obtained from electronic medical record review. RESULTS: The study cohort of 1714 women who delivered included White non-Hispanic (51.3%), Black non-Hispanic (26.3%), Hispanic (11.8%), Asian (7.3%), and other (3.3%) participants with a median age of 32 years. SARS-CoV-2 IgG and/or IgM antibodies were detected in 83 of 1471 (6%) mothers with matched mother and newborn sera available at delivery. Among newborns born to seropositive women, IgG was detected in 72 of 83 (87%) newborns. Infants born to seronegative mothers did not have any detectable antibodies, and IgM antibodies were not detected in any cord blood sample. Most seropositive women (60%) were asymptomatic for COVID-19. None of the infants born to seropositive mothers tested positive to SARS-CoV-2 by PCR between 24 and 48 hours after birth. Neonatal cord blood IgG concentrations were positively correlated to maternal IgG concentrations (r = 0.886, P < .001). Placental transfer ratios were associated with time elapsed from maternal infection, defined as time of symptom-prompted PCR testing, to delivery (r = 0.620, P < .001). Transfer ratios were not associated with infection severity. Ratios more than 1.0 were observed among all disease severities, including those asymptomatic. Antibody transfer ratios increased as time increased between onset of maternal infection and delivery. CONCLUSIONS: Maternal IgG antibodies to SARS-CoV-2 were transferred across the placenta in symptomatic and asymptomatic infection in pregnancy. Neonatal cord blood antibody concentrations correlated with maternal antibody concentrations and with the length of time between onset of infection and delivery.