To evaluate the maternal immune response to SARS-CoV-2 infection during pregnancy and to assess the effectiveness of transplacental antibody transfer was the purpose of the study. Researchers collected matched maternal and cord blood samples at the time of delivery from pregnant patients who tested positive for SARS CoV-2 infection at any stage during pregnancy. Maternal plasma and cord blood quantities, as well as the neutralizing efficacy of immunoglobulin (Ig)G, IgA, and IgM antibodies directed against the SARS-CoV-2 spike protein, were measured using an enzyme-linked immunosorbent assay (ELISA) and neutralization tests. A total of 32 matched samples were examined. Anti–receptor-binding domain IgG was found in 100% of maternal blood samples and 91% of cord blood samples. Functional neutralizing antibodies were found in 94% of the maternal blood samples and 25% of the cord blood samples. When compared to asymptomatic infection, symptomatic infection was linked with a substantial difference in median maternal anti–receptor-binding domain IgG titers. When comparing patients who delivered more than 14 days following a positive PCR test result to those who delivered within 14 days, median maternal anti–receptor-binding domain IgG titers were not substantially greater in those who delivered within 14 days.

These findings show a strong maternal neutralizing and anti–receptor-binding domain IgG response following SARS-CoV-2 infection, but lower-than-expected effectiveness of transplacental antibody transfer and a substantial drop in neutralization between maternal and cord blood. Maternal infection does give some level of neonatal antibody protection, but the strength and duration of this protection need to be investigated further.