The aims of this retrospective study were as follows: (i) to report about atypical kinetics of virus-specific IgM antibody response and early IgG avidity maturation within 90 days after the onset of primary HCMV infection in a population of pregnant women; (ii) to assess the frequency of such results together with the resulting risk of missing or misdiagnosing a primary HCMV infection in pregnancy. This evidence concerns the gene CD40LG and cytomegalovirus infection.