Comparative value of polymerase chain reaction and conventional biological tests for the prenatal diagnosis of congenital toxoplasmosis.

When toxoplasmosis is acquired during pregnancy, there is a risk of severe congenital defect in the foetus. Maternal treatment with spiramycin limits the transplacental passage of the parasite to the foetus but does not prevent infection in all cases. Prenatal diagnosis should be based on specific and fast methods to prescribe the more potent combination of sulfadiazine and pyrimethamine. This study evaluates PCR in the prenatal diagnosis of toxoplasmosis; PCR was based on the detection of the gene coding for the P30 surface protein. Amniotic fluid from 44 women with suspected foetal infection was tested by PCR and results were compared to those of conventional diagnostic tests on foetal blood and amniotic fluid. PCR was positive in 7 out of 10 samples from proven congenital toxoplasmosis cases. Sensitivity of PCR was similar to cell culture and mouse inoculation of amniotic fluid but was superior to tests carried out on foetal blood (specific IgM, eosinophil and platelet counts, gamma glutamyl transferase, mouse inoculation). In two cases, PCR was positive with no detected infection of the foetus. In this study, the combination of fast detection methods, ie cell culture and PCR of amniotic fluid, eosinophil and platelet counts, GGT activity and specific IgM, enabled us to confirm 10/10 cases of congenital toxoplasmosis in less than a week. PCR therefore appears to be an additional test which improves early prenatal diagnosis of toxoplasmosis.