Prenatal Diagnosis Flashcards
What does prenatal dx allow clients?
timely treatment of condition (before or after birth)
decision-making about continuing pregnancy
prenatal and neonatal management
time to plan and prepare psychologically, socially, etc
Who should be offered prenatal dx? in common practice?
everyone
fetal anomalies on US abn screening result previous child with genetic condition AMA FHx of genetic condition of ONTD
What does CVS sample? When is it completed?
chorionic villi
should be representative of fetus
10-14wks GA
What type of studies can be used with CVS?
cyto, molecular, biochemical
What types of CVS can be done? Patient decision?
transcervical, transabdominal
no
What are the risks associated with CVS?
1/100-1/200 (new studies say closer to 1/500)
What types of results can be seen in CVS? accuracy?
1%: mosaic
1% maternal cell contamination
99% detection of chromosomal adn
Limitations of CVS?
No ONTD info -> MS_AFP only @ 16-18wk and anat scan at 18-20wks
pt cannot choose method
mosaic results require follow up
What % of mosaic results in CVS are true mosaicism? What’s the other percentage make up?
10-20%
80-90% confined placental mosaicism
What are the outcomes of CPM? What chromosomes have higher rate of CPM? Follow up for CPM?
generally good
possible increased risk of fetal growth restriction
trisomy 13, monosomy X, rare autosomal trisomies
amnio
What cells are present in amniotic fluid that can be used?
skin and fetal urogenital tract
What types of studies can be done from amniotic samples?
cells -> cyto, molecular, and/or biochemical
fluid -> AF-AFP, AChE and/or biochem
When is amnio done?
16-20wks ideally
15wks-delivery (amnion and chorion must be fused)
What are some other indications for amnio?
fetal lung maturity
dx of infection/other conditions
treatment/therapy (amnio drainage/reduction)
What are the risks associated with amnio?
complications leading to pregnancy loss/preterm labor -> 1/200-1/400 (most recently maybe 1/500-1/1000)
How accurate is amnio?
99.5% DR for chromosome abn
98% of ONTDs by AFP
- High AFP -> AChE analyzed -> >99% DR for ONTD
Caveats to amnio?
procedure can be difficult/impossible if:
- anterior placenta
- mulitple pregnancy
- maternal obesity (more painful)
- low amniotic fluid (oligohydramnios)
What types of anticipatory guidance is given to those with invasive prenatal testing?
complications:
- fever or chills not related to cold/flu
- heavy, rhythmic contractions lasting 2-3 hrs or more
- fluid leakage from vagina
- bleeding from vagina (spotting is common after transcervical CVS)
What is PUBS? When is it completed? Accuracy?
AKA cordocentesis -> samples fetal blood from umbilical vein under US
roughly 20wks
99.9% DR for chromosome abn
Why is PUBS done? Uses?
detect and treat blood conditions
fetal hematologic status fetal blood transfusion/delvier meds congenital infection eval rapid karyotype follow-up mosaicism (not often)
Risks with PUBS?
2-5% risk of miscarraige (dependent on provider) - fetal bleeding from puncture - cord hematoma - fetal bradycardia - infection -fetal-maternal bleeding pregnancy loss
What test does ACOG be recommended for any pt undergoing invasive testing?
CMA
What types of FISH exist? Probes?
Interphase (count) and Metaphase (identify)
chromosome specific probes
locus specific
When would you use interphase FISH? Caveats?
rapid identification of common aneuploidy (same chromo as NIPT)
cannot detect structural abn or numerical abn of other chromosomes
usually ordered with karyotype and/or array to get early results
Limitations of Interphase FISH?
maternal cells are not distinguished
considered a screen (an not considered dx)
Why would you use Metaphase FISH?
identify location of particular DNA seq (often for specific fetal microdeletion)
Caveats of Metaphase FISH?
Longer TAT than interphase, require cultured samples
What are karyotypes used for?
identify aneuploidy, structural rearragements and chromosomal abn >5-10Mb
Caveats to karyotype?
cell culture req (longer TAT)
low resolution
When would you use a CMA?
detect clincally sig chromosome CNV too small to be seen on karyotype
Caveats for CMA?
not useful for single gene (incidental dx may arise) cannot deetct balanced translocations cannot detect triploidy may detect consanguinity (ROH) can report VUS
Benefits of CMA?
can be performed on culture or uncultured cells
prenatal CMA interpreted diff than ped or adult CMA
detected 1.7% of variants in fetus with normal US and karyotype, 6% of fetuses w US abn and normal karyotype
What should we consider when ordering prenatal dx?
utility (what does it provide for the pt)
how pregnant is the pt?
what is TAT and how would this limit their options?
client values, priorities, and needs
limitations
