PRENATAL-DIAGNOSIS OF CONGENITAL TOXOPLASMOSIS WITH A POLYMERASE-CHAIN-REACTION TEST ON AMNIOTIC-FLUID

Background. Congenital infection with Toxoplasma gondii can produce se rious sequelae. However, there is little consensus about screening dur ing pregnancy, and the tests used to establish a prenatal diagnosis of toxoplasmosis are complex and slow. We evaluated a simpler approach t hat is based on a polymerase-chain-reaction (PCR) test. Methods. Prena tal diagnostic tests, including ultrasonography, amniocentesis, and fe tal-blood sampling, were performed in 2632 women with T. gondii infect ion acquired during pregnancy. In 339 consecutive women, a competitive PCR test for T, gondii was performed on amniotic fluid, and its resul ts were compared with those of conventional diagnostic tests. The PCR test targets the B1 gene of T. gondii, uses an internal control, and c an be completed in a day. Positive tests were confirmed by serologic t esting of newborns or by autopsy in terminated pregnancies. Results. O verall, the risk of fetal infection was 7.4 percent, but it increased sharply with gestational age. Congenital infection was demonstrated in 34 of 339 fetuses by conventional methods, and the PCR test was posit ive in ail 34. In three other fetuses, only the PCR test gave positive results, and follow-up testing confirmed the presence of congenital t oxoplasmosis. The PCR test gave one false negative result but no false positive results. The PCR test performed better than conventional par asitologic methods (sensitivity, 97.4 percent vs. 89.5 percent; negati ve predictive value, 99.7 percent vs. 98.7 percent). Conclusions. For the prenatal diagnosis of congenital T. gondii infection, an approach based on a PCR test performed on amniotic fluid is rapid, safe, and ac curate.