A 20 week old pregnant woman presents to her GP with a 2 week history of general malaise, sore throat and swollen glands in her neck. Her GP orders Cytomegalovirus (CMV) serology. Her CMV IgM is low reactive and CMV IgG is moderately reactive.

1) Why is the diagnosis of CMV infection in pregnancy important?

Because of the risk of intra-uterine transmission of the virus leading to congenital CMV infection.

2)What other tests could/should the GP have requested?

Given that the patient is pregnant I think the full range of Infectious Monocleosis like illnesses should be screened for here, EBV, CMV, Toxoplasmosis and HIV. I would also do a Full Blood Count to see whether there is a relative lymphocytosis with atypical lymphocytes present. There is also an argument for Liver Function Tests (LFTs) but where do you stop….

3) How can the laboratory clarify whether this is a CMV infection occuring during pregnancy?

• As the CMV IgM is low reactive, I would recommend repeating it. It is also important to check what the EBV(VCA) IgM is to exclude a cross-reaction.
•  Ante-natal “booking” bloods should have been taken at 12-14 weeks gestation and serum should be stored. Important to go back and test this stored serum to see if an IgG seroconversion can be demonstrated.
•  Also worthwhile taking current serum and performing CMV IgG avidity testing. I the avidity is low then this indicates more recent infection and thus the probability of the CMV infection having occured during pregnancy.
•  Requesting repeat CMV serology from the patient in 2-4 weeks looking for any change in CMV IgM and IgG titres.

See this article for a comprehensive look at CMV testing in pregnant women.