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)
| Test | Timing (Gestational weeks) | Components | Conditions |
| 1st trimester combined screening | 11–13 | Nuchal 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 | 15–20 | HCG 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 | 15–20 | Quad test – Inhibin A | |
| Sequential integrated test | 10-13 then 15–20 | 1st trimester combined + Quad | |
| Cell-free fetal DNA testing(cffDNA) | >10 | Fetal 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 |
I believe AFP is normal for Patau syndrome
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.
cffDNA testing can also be used to predict fetal blood type when the mother has an alloantibody capable of causing HDFN.