Polymerase chain reaction (PCR) is a method of duplicating
DNA strands from a tiny sample of blood, hair, or
tissue. PCR is used to identify infectious diseases, genetic conditions, and
genetic links between people.
When a pregnant woman has
toxoplasmosis, a PCR test on
amniotic fluid is used to learn whether her fetus is
also infected. PCR is preferred over a fetal blood test for
antibodies because:1
- Collecting amniotic fluid through
amniocentesis is considered safer than fetal blood
sampling.
- PCR is better than antibody testing to detect
toxoplasmosis.
- PCR can be done earlier in a pregnancy than a blood
test for antibodies. Because first- and second-trimester fetal infection carry
the highest risk of birth defects and mental retardation, earlier test results
are important to parents who are considering ending such a pregnancy.
In rare cases, PCR produces
false-positive or
false-negative test results. Follow-up testing and
fetal ultrasound monitoring for
hydrocephalus can help confirm PCR test
results.
PCR is seldom used to diagnose toxoplasmosis in adults. Antibody
testing of a blood sample is easier and more widely available.
Citations
Jones J, et al. (2003). Congenital toxoplasmosis.
American Family Physician, 76(10): 2131-2138.
