Evolution in screening of Down syndrome TOG 2018 Flashcards
What proportion of mothers are >35years?
> 20%
T21 detection rate and false positive rate of screening by maternal age
Detection 30%
False +ve 5%
What material serum markers are associated with T21
Low AFP/unconjugated estriol, PAPP-A
High b-hCG & inhibin
T21 detection rate and false positive rate of screening by serum markers
Detection 60-75%
FP 5%
When can NT be assessed on USS?
11-13 weeks
Which markers are used in combined screening
NT
bHCG
PAPP-A
Maternal age
T21 detection rate and false positive rate of screening by combined screening. If twins?
Detection 90%
FPR 5%
Similar for twins
DCDA - individual risk
If MC twins FPR 10%, average of both twins
Difference in combined screening serum markers between T21, T18,T13
T18/13: b-hCG decreased
T21: b-h-CG increased
All other markers the same
What is the minimum fetal fraction to perform NIPT?
4%
T21 detection rate and false positive rate of screening by cell-free DNA test?
Detection 99%
FPR 0.1%
Table summarising detection rate and FPR rate of T21
What proportion of cell-free fetal DNA is no results given? On second sample what proportion receive a result?
1-5% no result
60% 2nd time, result given
What factors increase risk of no result?
Material obesity
Small placental mass - seen in T18/T13 - higher failure rates
What % of pregnancies are twins? Ration DC to MC?
3%
7:3
Can NIPT be offered to twins?
MC - Yes, performance similar to singleton
DC - caution as may give false result, euploid fetus can give more DNA than aneuploidy, Dx may be missed
Table showing cute offs of combined screening risk and effect on false +ve rate, detection T21, T18/13
