Prenatal diagnosis of congenital toxoplasmosis.

Ninety-three pregnant women with Toxoplasma gondii seroconversion during pregnancy underwent prenatal diagnosis of fetal toxoplasmosis. The following tests were used: (1). amniocentesis for mouse inoculation (93 subjects), (2). amplification of T. gondii DNA by polymerase chain reaction (PCR) (79 subjects), and (3). cordocentesis for the detection of T. gondii-specific IgM antibodies (13 subjects). All patients had serial ultrasonographic scans to detect those fetuses with abnormalities that could be associated with congenital toxoplasmosis. Eighteen pregnancies (19.4%) had evidence of vertical transmission. A total of 11/18 (61.1%) had positive amniotic mouse inoculation test, while 10/12 (83.3%) had positive PCR results. The combination of both tests allowed the prenatal diagnosis in 17/18 infected fetuses (94.4%). All patients who underwent cordocentesis for the detection of T. gondii-specific IgM antibodies had negative results. However, in two of the above cases fetal toxoplasmosis was detected by amniotic fluid studies. In five of the infected fetuses there were abnormal ultrasonographic findings. All pregnancies with evidence of vertical transmission were terminated, whereas the remaining pregnancies proceeded normally to term. The present data showed that amniotic fluid studies, preferably PCR amplification of T. gondii DNA, are the best diagnostic tools for the detection of vertical transmission in pregnancies with seroconversion during pregnancy.