[Biological diagnosis of toxoplasmosis in the course of pregnancy: methods, interpretations and practical recommendations].

The biological diagnosis of infection with Toxoplasma gondii during pregnancy can be performed: either (1.) with direct methods (microscopic examination, in vitro isolation on cell cultures, histology, detection of T. gondii DNA) or (2.) by indirect serological methods in order to demonstrate specific antibodies in serum. An appropriate combination of complementary techniques (antibody detection in serum and demonstration of the parasite) must lead, in the majority of cases, to a precise diagnosis of congenital toxoplasmosis. Serological examination of a woman before or at the beginning of pregnancy serves to distinguish between women with or without specific immune status. The diagnosis of a seroconversion during pregnancy causes few difficulties particularly if carefully followed up. However, it is rather difficult to date an infection during pregnancy based only on a initial positive sample with the presence of anti-T. gondii IgM. Thus, around 1 to 5% of serological examinations during pregnancy cause practical problems of interpretation. A certain number of recommendations are suggested to the laboratory supervisor: 1. Pregnant women should be systematically tested for specific anti-T. gondii IgG or total Ig and IgM. The choice of the techniques serves to reliably distinguish women without anti-T. gondii antibodies (women at risk for primary infection) from those with anti-T. gondii antibodies (immune women). 2. Interpretations of results should be well formulated to be understandable to the practitioner who must adequately inform the patient and determine the proper medical action on the basis of the serological results. 3. Sera should be preserved systematically for a minimum of 12 months (whatever the results may be). 4. Cases or situations causing problems should be referred to a specialized laboratory for expert advice.