Interpretation of CMV serology in early pregnancy

CMV antibodies	IgG avidity	Interpretation	Implications
IgM– and IgG–	Not applicable	Uninfected or very early infection	Counsel about behavioral measures to reduce risk of acquiring infection
IgM+ and IgG–	Not applicable	Early primary infection or false positive (90%) due to another virus, autoimmune disease, laboratory methods	Repeat in two weeks Consider ancillary testing for features of acute infection: complete blood count, liver chemistries, blood or urine CMV PCR
IgM+ and IgG+	Low	Recent infection (within 2 to 4 months) Seroconversion is diagnostic of primary infection	Counsel about likelihood of fetal infection, possible sequelae, and options for prenatal diagnosis and management
IgM+ and IgG+	High	Excludes recent primary infection (within 3 months) A significant rise (at least double) in serial IgG titers suggests reactivation or reinfection	Counsel about low risk of fetal infection, but possible sequelae if fetus is infected
IgM– and IgG+	High	Excludes recent primary infection (within 3 months) Absence of a significant rise in serial IgG titers suggests absence of reactivation or reinfection	Counsel about low risk of fetal infection and possible sequelae No need for further testing
IgM– and IgG+	Low	Unclear because all validation studies of avidity have been in the setting of true positive IgM

CMV: cytomegalovirus; IgG: immunoglobulin G; IgM: immunoglobulin M; PCR: polymerase chain reaction.

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