Pitfalls of prenatal diagnosis associated with mosacisim TOG 2022 Flashcards
When testing cell free fetal DNA in NIPT (non invasive prenatal testing) what cel are being tested
Fetal fraction of DNA in maternal blood, derived from apoptosis of the external layer of the placenta or trophoblast.
How common is fetal placental mosaicism?
2-3%
What is the most common reason for retrospectively positive NIPT results?
Confined placental mosaicism
Chromosomal non dysjunction occurs from what error?
Non-dysjunction
In mocosiam - an abnormal cell line can be present in both fetus & placenta, only fetus or only placenta?
Which is the most common?
Confined placental mocosiam
How common is mosaic in chorionic villus sample?
1-2%
Increases with gestation, hence beyond 15 weeks amniocentesis
Table showing combined placental mosaicism and true fetal mosaicism types and NIPT results
If CVS is performed after high risk NIPT which types of CPM may give false +ve
CPM types 1 and 3 - abnormal cytitrophoblast but normal fetus
Most common in trisomy 13 (patau) and 18 (Edward)
Which type of true fetal mosaicism may have false -ve NIPT
TFM 5 - normal cytotrophblast, abnormal fetus
combined placental mosaicism is associated with what risks in pregnancy?
FGR, fetal loss - regular growth USS
UK best practice to test cell lineages in CVS
QF-PCR
Which aneuploidy is NIPT the least sensitive for?
Trisomy 13 - Pataus
Which aneuploidy has highest risk of false negative and false positive?
Monosomy X 45, X
(then for false -ve T18, false +ve T13)
Risk of mosaicism in CVS after high risk NIPT for
- MX
- T13
- T18
- T21
- MX 59%
- T13 22%
- T18 4%
- T21 2%
If +ve NIPT without significant fetal structural anomaly
Consider optimal diagnostic invasive test - discuss limitations and essential to refer to clinical genetics
