Dual Marker/Combined
test
Dual marker screening test assesses the possibility of Down’s syndrome (trisomy 21) and Edward’s syndrome
(trisomy 18) in the fetus by analysing the biochemical levels of 1) Free Beta HCG (human chorionic
gonadotropin) and 2) PAPP-A (Pregnancy
Associated Plasma Protein) in maternal blood.
But what is Combined Screening ?? Ans: Combined
Screening involves a
combination of A) biochemical markers
with B) USG markers (Nuchal Translucency
& Nasal Bone) in the first trimester. Combined screening further offers
high detection rate for chromosomal abnormalities. It is usually performed
after 8 weeks of pregnancy up to 14 weeks.
|
Markers
|
Free hCGβ + PAPP-A + NT + NB + FHR
|
|
Time of test ( in weeks)
|
11-13+6 weeks
|
|
Detection rate ( % )
|
95 %
|
|
False positive rate ( % )
|
3 %
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