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.