INTRODUCTION
Whether vertical transmission of SARS-CoV-2 from mother to child may occur during maternal infection in pregnancy is still unclear (1, 2). Possible mechanisms of prenatal transmission between mother and child include transplacental transmission and ascending infection from the vagina through the cervix. Intrapartum and postpartum transmission might happen through fetal ingestion or aspiration of vaginal and fecal secretions during vaginal delivery, through respiratory droplets, or breast feeding (1). Few studies have detected SARS-CoV-2 in vaginal secretions (3-6). A recent case report from Sweden found evidence of transplacental vertical transmission of SARS-CoV-2 in gestational week 35 (7).
The presence of antibodies in fetal blood might offer protection of the fetus and child against COVID-19 during pregnancy, vaginal delivery, and in the neonatal period. SARS-CoV-2 total antibodies have been detected in less than 40% of non-pregnant individuals within the first week after infection (8). One study showed that the SARS-CoV-2 antibody titre remained stable from infection in the first trimester until delivery, but the exact timing of maternal seroconversion was not investigated (9). Other studies have examined the presence of SARS-CoV-2 antibodies at delivery in blood samples from the umbilical cord or the offspring of mothers with COVID-19. Some found anti-SARS-CoV-2 IgG, others both IgM and IgG (3, 10, 11). Since IgG is the only antibody class that significantly crosses the placenta, findings of IgM in cord blood indicates in utero infection, while IgM in neonates could be caused by in utero infection as well as postnatal infection. Additionally, the timespan between maternal SARS-CoV-2 diagnosis and the presence of antibodies in umbilical cord has been assessed, however, findings have been ambiguous (3). Together, previous studies may indicate that the risk of vertical transmission is increased if the woman delivers less than one week from onset of infection.
The objective of this study was to investigate if SARS-CoV-2 is detectable in vaginal swabs of pregnant women diagnosed with COVID-19 and to study the presence and timing of SARS-CoV-2 antibodies in maternal and umbilical cord blood during and after COVID-19 in pregnancy.