Prenatal Testing Flashcards
Most common autosomal?
Most common sex chromosomal?
autosomal: trisomy 21
sex chromosomal: Klinefelter’s XXY
Difference between prenatal screening vs. testing?
screening: non-invasive
testing: more dx and (currently) invasive
can non-invasive testing give definitive answers?
yes
chromosomal microarrays give what kind of results?
uncertain clinical significance
molecular test
2 fetal sampling procedures?
Chorionic villus samping: get placental tissue
Amniocentesis: amniotic fluid for cell collection
What is FISH testing for chromosomes?
- fluorescent tags for specific chromosomes, trisomy or aneuploides
- fast, can be done in interphase
What is karyotyping?
- need dividing cells in metaphase
- takes 2 weeks
what is the disadvantage of microarrays?
though higher resolution, it can’t detect balanced translocations like karyotyping can
what is done in 1st trimester combined screening?
- blood test at 9-13 weeks - 2 biochem
- ultrasound at 11-13 weeks -
+ maternal age + algorithm = risk calculation
what 2 things are measured at 12-week ultrasound?
- nuchal translucency
2. crown rump length
what are the cut-offs for 1st trimester combined screening for T21? T18?
T21 - 1:300
T 18 - 1:175
what is done in 2nd trimester screening?
Blood at ~16weeks (4 biochems) \+ maternal age \+ algorithm
2nd trimester screening cut-offs? T21? T18? NTDs?
T21 - 1:250
T 18 - 1:200
NTDs: >2.0 MoM
What is Rearrangement in karyotyping?
- reciprocal translocation
- could be balanced (no phenotype)
What is Robertsonian translocation?
two acrocentric only chromosomes (13,14,15,21,22)
