Prediction of congenital toxoplasmosis by polymerase chain reaction analysis of amniotic fluid

Abstract

for the European Multicentre Study on Congenital Toxoplasmosis (EMSCOT) 1 Objective To determine the accuracy of polymerase chain reaction (PCR) analysis of amniotic fluid for fetal toxoplasmosis according to clinical predictors of outcome and study centre. Design Prospective cohort study.Setting Nine European centres.Population Women with suspected toxoplasma infection identified by prenatal screening.Methods Logistic regression was used to examine the effects of gestational age at maternal seroconversion, treatment and timing of amniocentesis, on PCR accuracy, and to calculate the post-test probability of congenital toxoplasmosis. Main outcome measures Infants had congenital toxoplasmosis if specific IgG persisted beyond 11.5 months.Uninfected infants had undetectable IgG in the absence of anti-toxoplasma treatment. Results Of 593 PCR results, 64 were positive (57 confirmed infected), and 529 were negative (23 confirmed infected). The likelihood ratio for a positive PCR result decreased significantly with trimester at seroconversion, but did not change significantly for a negative result. Weak associations were detected between sensitivity and, inversely, with specificity, and gestational age at maternal seroconversion. There was no significant association between sensitivity and centre, type or duration of treatment, or timing of amniocentesis. Specificity differed significantly between centres (P < 0.001). The change in pre-to posttest probability of infection was maximal for a positive PCR after first trimester seroconversion, affecting 1% of women tested, and a negative PCR after third trimester seroconversion, affecting half the women tested. Conclusions Prediction of the risk of congenital toxoplasmosis should combine estimates of test accuracy and maternal -fetal transmission, which take account of the gestational age at which the mother seroconverted. Local laboratory standards will affect the generalisability of these results.

Diagnosis, Treatment, and Prevention of Congenital Toxoplasmosis in the United States

“…On the contrary, for infections thought to be acquired in the third trimester, the NPV was lower, and a negative AF PCR assay result in such cases should be interpreted cautiously and would not exclude fetal infection ( Fig 8). 169,170 (The exact reason for this situation is not known. Some possible explanations could be a dilution effect attributable to a larger amount of AF in the third trimester and/or maternal treatment before AF PCR testing [eg, in cases in which P/S was initiated immediately after the diagnosis and before the AF was tested].)…”

“…Some possible explanations could be a dilution effect attributable to a larger amount of AF in the third trimester and/or maternal treatment before AF PCR testing [eg, in cases in which P/S was initiated immediately after the diagnosis and before the AF was tested].) 112,168,169 Moreover, it probably takes several weeks for the infection to cross the placenta from the mother to the fetus, in large enough quantities to spill into the AF. T gondii likely first infects the placenta, replicates, then crosses to the fetus.…”

“…The evidence for the diagnostic performance of AF PCR assay is summarized in Table 8, according to the results of the most recent studies published over the past 10 years. 112,168,169 The clinical value of AF PCR assay results in estimating a woman's risk of delivering an infant with CT varied according to gestational age at maternal seroconversion. Figure 8 shows how the probability of fetal infection (posttest probability) changed (as compared with the pretest probability) after a positive or a negative AF PCR assay result according to the gestational age at which the maternal primary infection most likely had occurred.…”

Clinical practice guideline. Integral Care Guidelines for the prevention, early detection and treatment of pregnancy, childbirth and puerperium complications: Section on toxoplasmosis in pregnancy

“…The PCR sensitivity seemed to increase with the age of the seroconversion, but was not influenced by maternal treatment 49 (Level of Evidence Ib)…”

Toxoplasmosis in Pregnancy, a Rare Clinical Manifestation: A Case Report

“…The rate of nervous system defect in fetus decreases by the increase in the gestational age (5-7). The golden test to confirm fetus infection is polymerase chain reaction (PCR) for Toxoplasma gondii DNA in amniotic fluid (8,9). Prenatal treatment is justified to reduce the risk of serious neurological sequels (8).…”