Genetic Testing Flashcards
How is the risk of down syndrome assessed in pregnancy?
After 12 week scan Taking into account: Maternal age Blood hormone levels Nuchal translucency thickness Nasal bone Blood flow through foetal heart Other foetal abnormalities
Why is Nuchal translucency thickness important?
More than 3mm can indicate chromosome abnormalities
When is prenatal testing arranges?
Abnormal findings at scans
Increased risk of Downs
If previous pregnancy was affected with a condition
Parents are carriers
What are the aims of pre-natal testing?
Inform and prepare parents for the birth of an affected baby Allow in utero treatment Manage the remainder of pregnancy Prepare of complication during birth Allow termination
What are the different prenatal tests?
Scanning (Ultrasound/ MRI)
Non-invasive (Maternal blood test/ Cell-free foetal DNA)
Invasive (CVS/ Amniocentesis)
What are the different types of scanning used during pregnancy?
Ultrasound in pregnancy Early/ dating scan High level/ Anomaly scan Foetal MRI (20+ weeks) Foetal echo
What is maternal serum screening?
Tests maternal serum markers in the blood to detect increased risk of Downs
Whats is cell-free foetal DNA?
Non-invasie prenatal diagnosis
Analyses DNA fragments in the maternal plasma during pregnancy
What is NIPD?
Non invasive prenatal diagnosis Maternal blood test at 9 weeks Achondroplasia Thanatophoric dysplasia Apert syndrome
When is sexing offered as NIPD?
X-linked condition in family
What are the limitations of NIPD and NIPT?
Multiple pregnancies- cannot tell which foetus DNA is from
Difficult in women with high BMI- low proportion of foetal DNA
Invasive test may still be needed to confirm
What are the benefits of NIPS and NIPT?
Less invasive tests
No increased risk of miscarriage
Less expertise required to perform
Result can be obtained earlier
What is chorionic villus sampling?
11-14 weeks
1-2% risk of miscarriage
Transabdominal or transvaginal
Takes sample of chorionic villi
What is amniocentesis?
From 16 weeks
Sample of amniotic fluid
1% of miscarriage
What tests are done with the samples?
Test for genetic disorder in question
Karyotype if chromosomal abnormality in family
PCR for all
What is CGH array?
After concerns on 20 week scan
Looks for small imbalances in chromosomes
If something is found parents are tested
What is the process of CGH array?
Extract and label DNA
Hybridise and wash
Scan
Analyse data
What is trio exome?
Consider where foetus in previous pregnancy had significant anomalies
Exome is coding region of genes
What are other options for a couple other than prenatal diagnosis?
No prenatal testing Use of egg/ sperm donors Adoption Choose not to have children Pre-implantation genetic diagnosis
What are the two steps of adoption?
Registration and checks
Assessment and approval
Lengthy process
What are the steps of PGD?
Stimulation of ovaries Egg collection Insemination Fertilisation Embryo biopsy Embryo testing Embryo transfer Pregnancy test
What has to be thought about when facilitating decision making?
Previous experience Family situation Religion Personal beliefs Psychosocial situation Balancing miscarriage with genetic risks
