Although IgM response may be very transient and go undetected even in a recent primary infection, to the best of our knowledge, this is the first time that the early clearance of IgM antibody during the first three months after onset of primary HCMV infection has been described in a population of pregnant women, in whom stringent criteria for diagnosis and dating of primary infection were used. This evidence concerns the gene CD40LG and cytomegalovirus infection.