On suspicion of congenital infection, serum samples from the mother are first analysed, this may be followed by testing the amniotic fluid. The sero-diagnosis is primarily based on comparison between the prenatal testing serum and current serum sample from the pregnant woman. Sero-conversion from negative to positive during the pregnancy gives a definitive diagnosis. A significant increase in IgG antibodies and the presence of IgM and/or IgA is interpreted as a probable diagnosis. A single serum sample containing specific IgG, IgM and/or IgA antibodies can be an indication of primary infection of the mother (European Research Network 1995). In these cases it may be necessary to perform confirmatory tests. These include determination of IgG antibody avidity, investigation of amniotic fluid by PCR (Hohlfeld et al. 1994; Guy et al. 1996; Pelloux et al. 1998) and/or isolation of the parasite in vivo and/or in vitro.
In newborns suspected of having congenital infection, cord blood or/and EDTA blood could be collected and analysed for the parasite itself or its DNA. Furthermore, it is recommended that the antibody response be followed by collecting blood samples at birth and at the age of 3, 6 and 12 months to measure the IgG, IgM and IgA antibodies.
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