- screening for TORCH infections
TORCH is an acronym for a special group of infections that may be acquired by a woman during pregnancy.
Who is a candidate for the test?
Any pregnant woman who believes she may have been exposed to toxoplasmosis, hepatitis B, syphilis, herpes simplex, chickenpox, rubella, or cytomegalovirus is a candidate for screening and should notify her healthcare professional right away.
How is the test performed?
A small amount of blood is withdrawn from a vein in the arm and sent to the lab for testing. A blood test called an antibody titer is used to detect antibodies to any of the suspected TORCH organisms.
When an infection occurs, the immune system responds by making specific proteins called antibodies to fight the infection. If the immune system has not encountered the organism before, it takes some time to generate the first antibodies. These antibodies will remain in the system. Following any subsequent exposure, larger amounts of antibody will be made.
Thus, when the initial sample of blood is taken shortly after an exposure, a woman's body may not have had enough time to start making antibodies yet. However, a woman can have antibodies to the infection in her blood because of an old infection or from a vaccine.
A second sample of blood is usually taken 10 to 21 days later to see if blood antibody levels against the infection are rising. If so, then a new infection, instead of an old one, is probably present.
If antibodies in the blood are due to a previous infection and there has been no new infection, the level of antibodies will not rise with the second blood sample. This finding is reassuring for the woman because old infections usually cannot harm the unborn child, except in the case of herpes. Only new infections occurring during the early part of pregnancy usually put the unborn child at risk.
What is involved in preparation for the test?
No preparation is needed for this test.
What do the test results mean?
A "negative" test (no rise in the antibody titer) means that as far as can be ascertained, the woman did not contract a new TORCH infection. It is important to realize that because there are many other causes of birth defects, a negative TORCH screen does not guarantee a healthy baby.
A positive test means that high or increasing levels of antibodies were detected. This generally means that the mother has caught a new TORCH infection. A positive test does not mean that the baby will catch the infection or develop birth defects. However, close monitoring of the pregnancy may be advised.
Pregnancy ultrasound may be used to look for birth defects. This is an imaging test that uses sound waves to look at the baby inside the womb. The exact risk of having a child with birth defects depends on the specific TORCH infection. It also depends on when during the pregnancy the mother was infected. The healthcare professional will discuss the results in the event of a positive test.
Essentials of Obstetrics and Gynecology, 1996, Hacker et al.