Prenatal Diagnosis Flashcards
why is prenatal testing performed?
If suspicious of foetal disease, so:
- FH
- Past obstetric history
- Serum screening
- USS (12 week/20week anomaly)
What are the classifications of prenatal diagnostic testing?
Invasive
Non-invasive
What are invasive tests?
Amniocentesids
Chorion Villus Sampling
What are non-invasive tests?
USS
Viral serology
Cell free foetal DNA (cffDNA)
How does cffDNA work? What are its uses?
It is extracted from maternal blood
Used to:
- determine foetal blood group (for RhD Immunisation)
- Determine sex of foetus in X linked disorders
- Diagnose skeletal dysplasia
What does cffDNA increase with?
It increases with gestation
What are the three options resulting from a prenatal test?
- Continue with pregnancy (facilitates care at time of delivery and prepares parents for baby)
- Termination of pregnancy
- Termination, but provides information for future pregnancies
What is chorion villus sampling?
Take a sample of foetal trophoblast cells in the chorion villus
These are cells from the developing placenta
How is chorion villus sampling done?
Pass a needle under USS guidance through abdominal wall and uterus, into placenta (MOST COMMON)
Pass a fine catheter through cervix into placenta
What is the risk of miscarriage with CVS?
2%
What is amniocentesis?
Extraction of amniotic fluid (15-20ml)
How is amniocentesis done?
By passing a needle under USS guidance through abdo wall and uterus into amniotic cavity
Then aspirate fluid
What is the risk of miscarriage of amniocentesis?
1.9%
What is the advantage of CVS over amniocentesis?
CVS can be performed earlier in pregnancy where surgical termination of pregnancy is still possible
What is cordocentesis? How is it done?
Extraction of foetal blood
Needle under USS through abdo wall and myometrium into umbilical cord, at the point where it inserts into the placenta, to extract foetal blood
