DISCUSSION
As a new emerging and highly pathogenic coronaviruse, the transmission
routes of SARS-CoV-2 have not been fully elucidated. Especially, there
is a huge controversy regarding whether SARS-CoV-2 can be
transplacentally transmitted from infected mothers to their fetuses. DA
Schwartz2 ever reviewed
a total of 38 pregnant women with COVID-19 and didn’t found any evidence
that SARS-CoV-2 was able to undergoe intrauterine or transplacental
transmission. However, a neonatal case with pharyngeal swabs testing
positive by RT-PCR at 36 hours age was reported in China, but the
results of nucleic acid test of cord blood and placenta in this case are
negative, which do not support the diagnosis of intrauterine
transmission.4 Soon
afterwards, L Dong et
al3 reported a neonatal
case, with elevated IgM/IgG antibodies to SARS-CoV-2 and abnormal
cytokine test results, born to a COVID-19 mother at 2 hours of age,
indicating the possibility of vertical transmission in utero.
The neonatal case in our report had a manifestation of viral pneumonia
in chest CT on the day of birth and an elevated IgM level at 3 days age.
IgM provides the first line of defense during viral infections, prior to
the generation of adaptive, high affinity IgG response that is important
for long term immunity and immunological
memory.5 Because IgM
antibodies usually do not appear until 3 to 7 days after infection and
IgM can’t be transferred to the fetus through placenta, the elevated
serum IgM in our neonatal case indicates the possibility of vertical
transmission in the utero. The date on which the mother of the neonatal
case infected with SARS-CoV-2 is uncertain. According to the disclosed
history, the results of serum IgG/IgM level and chest CT results, we
speculate that the pregnant women was already in the recovery period on
admission. Thus, the fetus could have been exposed for the risk of
SARS-CoV-2 infection throughout the COVID-19 course of the mother. The
slightly increased IgM level and the significantly increased IgG level
of the neonatal case are also consistent with the serum characteristics
of infected patient in recovery period, which may explain that 3 repeat
oropharyngeal swab test was negative for SARS-CoV-2 in the neonate. Of
note, because the placenta and amniotic fluid were not collected and
detected for SARS-CoV-2 RNA, a direct evidence for intrauterine
transmission is still lack in our case report.