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 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)

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


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
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 testing Chromosomal aberrations (high specificity and sensitivity for trisomy 21 > trisomy 18 >trisomy 13)

Gender determination

2 Viewpoints 💬 on “Non-invasive Prenatal Screening”

    1. Hello Rasha, Thank you for the correction. AFP actually seems to be an unreliable marker for diagnosis of Patau syndrome (trisomy 13). Different resources quote that AFP to be decreased, normal or increased. Some fewer than 50% of affected babies may have open neural tube defects or ventral wall defects, where AFP may be increased. So, we will go with normal AFP for Patau syndrome.

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