Difficulties of interpretation in toxoplasma serology in a pregnant woman in the context of a maternofetal alloimmunization against HPA-1a platelet antigen

Serological status in case of Toxoplasma gondii infection needs to be established either before or at the beginning of a pregnancy. However, clinical biologists are often facing conflicting serological results that are difficult to interpret: we report here the case of a woman in her 30th week of pregnancy. Both her IgM and IgG were negative at the 14th week of pregnancy; but suddenly, starting from the 20th week, her IgG became positive while her IgM remained negative. We remind here of the most frequent hypothesis that can explain a sudden and isolated increase of anti-T. gondii IgG: Is it a technical problem (specificity)? Is it a drug interference? Eventually, we found that the patient was receiving, since the 16th week of pregnancy, every week an intravenous perfusion of polyvalent immunoglobulins. Since we didn't know if the IgG present in this perfusion can protect the patient against toxoplasmosis, we decided to consider this women as non immune.