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. However, 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 relatively new 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

1. Cunningham FG, et al. (2005). Prenatal diagnosis and fetal therapy. In Williams Obstetrics, 22nd ed., pp. 313–339. New York: McGraw-Hill.

2. Benn PA, et al. (2003). Incorporation of inhibin-A in second trimester screening for Down syndrome. Obstetrics and Gynecology, 101(3): 451–454.