Prenatal diagnosis of congenital toxoplasmosis in 261 pregnancies

Two hundred and sixty-one pregnant women underwent prenatal screening by cordocentesis and/or amniocentesis between 1987 and 1994. The following tests were used: (i) detection of anti-Toxoplasma gondii IgM, IgA, and IgE antibodies by immunocapture and the comparative immunological profile method based on enzyme-linked immunofiltration assay of fetal blood and (ii) direct detection of the parasite in cell culture and by mouse inoculation with fetal blood (FB) and/or amniotic fluid (AF). Of the 31 cases of congenital toxoplasmosis, 24 (77 per cent) were detected prenatally. Overall, the FB and AF inoculation methods were the most effective (50 per cent sensitivity with FB inoculation to mice and/or cell culture and 74 per cent with AF). However, antibody detection in FB was the only positive test in three cases. Of 18 surviving children diagnosed prenatally, only one developed chorioretinitis (9 months of age). Seven newborns (23 per cent) with negative prenatal tests were diagnosed by postnatal laboratory monitoring, but none of these children developed clinical toxoplasmosis. There may have been more false negatives, as only 48 per cent of unaffected children were followed up for at least 12 months. All the tests had a specificity of 100 per cent. Fetal blood sampling has considerable value but also carries some risks and is currently being abandoned in favour of amniocentesis alone with gene amplification and mouse inoculation.