CD40LG and viral infectious disease: IgM antibodies as part of the immune response to a specific viral infection, unlike IgG antibodies, cannot cross the placental barrier and can be useful in determining potential direct transmission to the fetus, but the weakness of this method is the existence of a cross-reaction and a false positive result, and the PCR test of the nasopharyngeal/oropharyngeal mucosa is the gold standard for determining the presence of SARS-CoV-2 infection in the newborns [70].