trisomy testing + twins

Question 1

standard initial testing for down’s, what is this made up of?

Answer 1

combined test, includes;
- nuchal transluceny measurement
- serum B-HCG
- Pregnancy-assoc plasma protein A (PAPP-A)

Question 2

what results of the combined test would make you concerned about downs

Answer 2

• thickened nuchal translucency
• raised HCG
• decreased PAPP-A

trisomy 18 (edwards) + 13 (patau’s) give similar but hCG tends to be lower

Question 3

downs testing based on weeks gestation

Answer 3

11-13+6wks = combined

15-20wk = quadruple

Question 4

what is the quadruple test made up of?

Answer 4

• alpha-fetoprotein (low in downs)
• unconjugated oestriol (low)
• hCG (high)
• inhibin A (high)

Question 5

the combined + quadruple test return either a higher or lower chance result - what does this mean?

Answer 5

lower chance - 1 in 150 chance or more (1 in 300)

higher chance = 1 in 150 or LESS (1 in 100)

Question 6

if a women has a “higher chance” result in combined/quadruple, whats the next test?

Answer 6

offered either;
a 2nd screening test = NIPT (non-invasive prenatal screening test)

diagnostic test = amniocentesis or chorionic villus sampling (CVS)

Question 7

non-invasive prenatal screening test (NIPT) test

Answer 7

• analyses small DNA fragments that circulate in blood of a pregnant woman (cffDNA)

cffDNA derives from placental cells + is usually identical to fetal DNA

Question 8

sensitivity of non-invasive prenatal screening test (NIPT) test for Downs

Answer 8

> 99% of sensitivity + specificity