Prenatal diagnosis using polymerase chain reaction on amniotic fluid for congenital toxoplasmosis

To evaluate sensitivity, specificity, and predictive values of a prenatal amniotic fluid (AF) polymerase chain reaction (PCR) test for diagnosis of congenital toxoplasmosis.

A multicenter prospective study was done on 271 women with proved primary Toxoplasma infection during pregnancy and who had amniocentesis for prenatal diagnosis by PCR. Live-born infants were eligible for analysis only if a serologic follow-up could assess a definitive infection status.

Of the 270 evaluable cases, 75 were congenitally infected, 48 of whom had a positive PCR at prenatal diagnosis. Overall sensitivity of PCR on AF was estimated at 64% (95% confidence interval [CI] 53.1%, 74.9%), negative predictive value of 87.8% (95% CI 83.5%, 92.1%), whereas specificity and positive predictive value were 100% (95% CIs 98%, 100% and 92.3%, 100%, respectively). Among cases with congenital toxoplasmosis, there were no significant differences between those with positive or negative PCR with regard to median gestational age at maternal infection, interval between maternal infection and amniocentesis, or duration of treatment before amniocentesis. However, sensitivity of PCR was found to be significantly higher for maternal infections that occurred between 17 and 21 weeks' gestation (P <.02).

A negative PCR of AF cannot rule out congenital infection. In this case, continuation of treatment with spiramycin combined with ultrasonographic follow-up and postnatal follow-up are warranted. Our results also suggest presumptive treatment combining pyrimethamine and sulfonamides in case of maternal infection occurring late in pregnancy.