Non-invasive Prenatal Screening

Quick review/Mnemonic:

PAPP-A is decreased in all trisomies.
Nuchal translucency is increased in all trisomies.

Inhibin A is only increased in Down’s syndrome.
Beta-HCG is increased in Down’s syndrome.

All triple test results decreased in Edward syndrome.

Only AFP is decreased in Patau syndrome.
Only AFP is increased in NTDs and abdominal wall defects.

Acetylcholinesterase level increased in Amniotic fluid is most specific marker for NTDs.

In Turner’s syndrome: All decreased in Quad test (if no hydrops) and like Down’s, i.e. increased HCG and Inhibin A (if hydrops)

fetus
TestTiming (Gestational weeks)Components Conditions
1st trimester combined screening11–13Nuchal translucency (NT) 

β-HCG

PAPP-A(pregnancy-associated protein A)
Down syndrome/Trisomy 21: ↑ HCG, ↓ PAPP-A, thickened NT

Edward syndrome/Trisomy 18: ↓ HCG, ↓↓ PAPP-A, ↑ NT

Patau syndrome/Trisomy 13: ↓↓ PAPP-A, ↑ NT

Neural tube defects: ↑ HCG
Quad screen test 15–20HCG
AFP
Estriol (uE3)
Inhibin A (DIA)
Trisomy 21: ↑ β-HCG, ↓ AFP, and ↓ uE3, ↑ DIA

Trisomy 18: ↓↓ β-HCG, ↓ AFP, and ↓↓ uE3, ↓ DIA

Trisomy 13: = HCG, ↓ AFP , = uE3, = DIA

Neural tube defects and Abdominal wall defects: = HCG, ↑ AFP, = uE3, = DIA
Triple screen test 15–20Quad test – Inhibin A
Sequential integrated test 10-13 then 15–201st trimester combined + Quad
Cell-free fetal DNA testing(cffDNA) >10Fetal DNA is isolated from a maternal blood specimen for genetic testingChromosomal aberrations (high specificity and sensitivity for trisomy 21 > trisomy 18 >trisomy 13)

Gender determination

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