Triple or quadruple serum screen and Down syndrome
The triple or quadruple serum screen estimates the
possibility that you may be carrying a fetus with
Down syndrome compared with other women of your age.
Risk for Down syndrome in a fetus increases as a mother's age increases,
particularly over age 35. For more information, see the topic Down Syndrome.
Unlike a diagnostic test, which actually detects a problem, the
triple or quadruple screen is only an estimate of the
chance that a problem is present.
If your serum screen result
estimates that your risk of carrying a fetus with Down syndrome is higher than
the average risk for your age, you can then choose to have a diagnostic test,
such as
amniocentesis. Amniocentesis provides amniotic fluid
that can be tested for Down syndrome and other chromosome abnormalities.
When considering your serum screen results, consider that this test has a
high
false-positive rate, meaning that test results suggest
a possible birth defect when one is actually not present. False-positive test
results are increasingly likely as you approach age 40 and can cause undue
stress and lead to unnecessary invasive testing (such as amniocentesis).
Similarly, negative test results can occasionally be wrong. But
the triple or quadruple screen does detect the vast majority of Down syndrome
fetuses, particularly in women who are older than 35. In this age group, at
least 80% of fetuses with Down syndrome are detected using triple or quadruple
screen. The older you are, the more likely the screen is to be
accurate.1
The quadruple screen combines
the triple screen and a test for the protein inhibin A, which is produced by
the fetus and the
placenta. In one large study of more than 23,000 women
of all ages, the quadruple screen detected almost 86% of all Down syndrome
cases. Based on this study, the quadruple test is more likely to pick up Down
syndrome and less likely to be false-positive than the triple screen.2
Citations
-
Cunningham FG, et al. (2005). Prenatal diagnosis and
fetal therapy. In Williams Obstetrics, 22nd ed., pp.
313–339. New York: McGraw-Hill.
-
Benn PA, et al. (2003). Incorporation of inhibin-A in
second-trimester screening for Down syndrome. Obstetrics and Gynecology, 101(3): 451–454.
Last Updated:
November 28, 2008
Cunningham FG, et al. (2005). Prenatal diagnosis and
fetal therapy. In Williams Obstetrics, 22nd ed., pp.
313–339. New York: McGraw-Hill.
Benn PA, et al. (2003). Incorporation of inhibin-A in
second-trimester screening for Down syndrome. Obstetrics and Gynecology, 101(3): 451–454.
