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3.b Will this test detect all cases of Down's?




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This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (gazissax@netcom.com) with numerous contributions by others.

3.b Will this test detect all cases of Down's?

No. 25% of the cases of Down's will result in abnormal AFP, while 60% of
the cases will register as an abnormal triple screen.
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Addition by Dr. Tim Reynolds:

Above line incomplete:

The detection rate is dependant on maternal age: in young women (age
12-16), the average detection for a multi-marker test will be about 40-45%
and for an AFP only test, about 20% (There is NO SANE REASON for testing
for Down's using AFP only: this is completely superceeded by multimarker
testing). In older women the detection rate for the Down's screen is much
higher and can be up to 90-95% in women aged 45+. The 60% figure quoted in
most women's magazines is the average detection rate for a normal
population assuming all women are screened. If all women over 35 get an
amnio and only younger women are screened, the apparent success of the
screening test will look poorer: If only older women get screened, the
apparent success rate will look better (Many of the differences in
detection rates for different screening combinations can at least partially
be explained by age distribution differences in the study populations).
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