Abstract
Objective: The immune system of pregnant women undergoes several changes over the course of pregnancy. In the past, these changes have been associated with increased susceptibility to viral respiratory infections such as SARS-CoV-1 and influenza. Our primary objective was to investigate the differences in immune response to SARS-CoV-2 infection in pregnant women compared to non-pregnant women over time. Design: This was a prospective, laboratory-based longitudinal observational study of pregnant women who have been infected with SARS-CoV-2 to determine the effects of pregnancy on the serological response post infection compared to their matched non-pregnant women. Methods: Participants were recruited between September 2020 and June 2021 who all tested positive for SARS-CoV-2 infection using PCR or serology. Changes in the SARS-CoV-2-specific IgG titres were measured in blood samples that were collected from 51 pregnant and 52 non-pregnant women of reproductive age at approximately 7–14 days, 1-month (±7 days), 4 (±1 month), and 8 (±1 month) months post-infection, respectively. A chemiluminescent immunoassay was used to assess the IgG response to SARS-CoV-2 using serum from infected participants. Antibody levels to SARS-CoV-2 spike RBD (receptor binding domain) and nucleoprotein were measured as a relative light unit (RLU). Results: We found a reduction in seroconversion rate at 7–14 days post-infection in pregnant women compared to non-pregnant women with 63.33% compared to 100%, respectively. Longitudinal assessment highlighted a significant decline in anti-spike RBD IgG (20-fold reduction) at 151 days (or 5 months and 11 days; p < 0.05) in pregnant women versus 241 days (or 8 months and 17 days; p < 0.01) in non-pregnant women. This showed that the fall in antibody levels occurred 3 months earlier in pregnant individuals. Conclusions: The data in this study demonstrates a delayed antibody response observed in pregnancy, where lower seroconversion rates for anti-spike RBD were detected at 7–14 days post-infection as well as an earlier decline in antibody levels which may indicate an overall delayed stimulation of the adaptive immune response. Future work will assess the response of B and T lymphocytes as well as neutralising antibodies to better understand the mechanisms at play.