Down's Syndrome

Question 1

What screening is conducted for Down’s syndrome?

Answer 1

Combined test
Nuchal translucency measurement + serum B-HCG + pregnancy-associated plasma protein A (PAPP-A)
Conducted at 11-13+6 weeks

Quadruple test
Alpha-fetoprotein, unconjugated oestriol, human chorionic gonadotrophin and inhibin A
Conducted at 15-20 weeks

Question 2

How are the results of the combined screening test interpreted?

Answer 2

Down’s syndrome is suggested by ↑ HCG, ↓ PAPP-A, thickened nuchal translucency

trisomy 18 (Edward syndrome) and 13 (Patau syndrome) give similar results but the hCG tends to lower

Question 3

What 3 conditions can a quadruple test provide information on?

Answer 3

Down’s Syndrome
Edward’s Syndrome
Neural tube defect

Question 4

How are the results of a quadruple test interpreted?

Answer 4

Down’s Syndrome:
AFP down, Uncon. E2 down, hcG up, inhibin A up

Edward’s Syndrome:
AFP down, Uncon. E2 down, hcG down, inhibin A normal

Neural defects:
AFP up, Uncon. E2 normal, hcG normal, inhibin A normal

Question 5

How are the results of the combined screening and quadruple test provided?

Answer 5

‘lower chance’: 1 in 150 chance or more e.g. 1 in 300
‘higher chance’: 1 in 150 chance or less e.g. 1 in 100

Question 6

If a higher chance is detected in combined screening and quadruple test, what is offered next?

Answer 6

Non-invasive prenatal screening test (NIPT) or a diagnostic test (amniocentesis, chorionic villus sampling)

Question 7

How does NIPT work?

Answer 7

analyses small DNA fragments that circulate in the blood of a pregnant woman (cell free fetal DNA, cffDNA)
cffDNA derives from placental cells and is usually identical to fetal DNA
analysis of cffDNA allows for the early detection of certain chromosomal abnormalities

Question 8

How accurate is NIPT?

Answer 8

Sensitivity and specificity are high for trisomy 21 (>99%)
Private companies offer it from 10 weeks gestation