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.