High cytomegalovirus IgG avidity is a reliable indicator of past infection in patients with positive IgM detected during the first trimester of pregnancy.

Objective: To evaluate the accuracy of high cytomegalovirus (CMV) specific IgG avidity in excluding recent infection in patients with anti-CMV IgM antibodies detected during the first trimester, using amniotic fluid obtained by standard amniocentesis.

Methods: Records of all patients with a positive anti-CMV IgM with IgG avidity >65% detected during pregnancy were reviewed. Amniocentesis for CMV assessment was offered to all patients. The presence of the virus in amniotic fluid was determined by polymerase chain reaction (PCR) and shell vial testing.

Results: Seventy-nine patients with a positive CMV IgM-high IgG avidity combination were identified. The serological tests were performed during the first trimester in 65 (82.3%) patients, of which 28 consented and underwent amniocentesis. All amniotic fluid samples were negative for CMV-PCR and CMV shell vial testing.

Conclusions: IgG avidity above 65% is a good indicator of past infection, and thus excludes CMV in the amniotic fluid. In such circumstances, invasive prenatal diagnosis may eventually not be required. This optimistic conclusion, however, needs to be confirmed by large scale studies.