[Toxoplasma gondii serology in pregnant woman: characteristics and pitfalls].

Screening program of congenital toxoplasmosis depends principally on serological testing and follow-up of pregnant women with negative serology from the onset of pregnancy. This program is particularly efficient because the majority of cases of obstetrical seroconversion are diagnosed and followed up. Serological techniques have evolved with time and are many on the market. The "IgG" tests are more and more specific at the detriment of their sensitivity. The latter is variable from one technique to the other. In 2008, despite the presence of an international standard, serological titrations are particularly variable making interpretation of the kinetics impossible between two different series, two techniques or two laboratories. In cases of interpretation discordance or borderline values, it is useful to do a confirmatory technique. The dye test or the western blot are useful in these cases and prevent up to 2 to 8% of unnecessary obstetric follow up. IgM tests are becoming more and more sensitive and precocious. These tests frequently detect "non specific IgM" as well as "residual IgM" (associated with a stable positive IgG titre). In such cases and in the absence of a preceding positive result, a complementary test done by specialized laboratories (such as ISAgA IgM or IgA, IgG avidity test, differential agglutination, etc.) is indispensable in order to prevent any error of interpretation. These complementary tests as well as the serological evolution (control done in 15 days) permit, in a large number of cases, to reassure the patient with full confidence.