Genetic Testing

Question 1

How is the risk of down syndrome assessed in pregnancy?

Answer 1

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

Question 2

Why is Nuchal translucency thickness important?

Answer 2

More than 3mm can indicate chromosome abnormalities

Question 3

When is prenatal testing arranges?

Answer 3

Abnormal findings at scans
Increased risk of Downs
If previous pregnancy was affected with a condition
Parents are carriers

Question 4

What are the aims of pre-natal testing?

Answer 4

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

Question 5

What are the different prenatal tests?

Answer 5

Scanning (Ultrasound/ MRI)
Non-invasive (Maternal blood test/ Cell-free foetal DNA)
Invasive (CVS/ Amniocentesis)

Question 6

What are the different types of scanning used during pregnancy?

Answer 6

Ultrasound in pregnancy
Early/ dating scan
High level/ Anomaly scan 
Foetal MRI (20+ weeks)
Foetal echo

Question 7

What is maternal serum screening?

Answer 7

Tests maternal serum markers in the blood to detect increased risk of Downs

Question 8

Whats is cell-free foetal DNA?

Answer 8

Non-invasie prenatal diagnosis

Analyses DNA fragments in the maternal plasma during pregnancy

Question 9

What is NIPD?

Answer 9

Non invasive prenatal diagnosis
Maternal blood test at 9 weeks
Achondroplasia
Thanatophoric dysplasia
Apert syndrome

Question 10

When is sexing offered as NIPD?

Answer 10

X-linked condition in family

Question 11

What are the limitations of NIPD and NIPT?

Answer 11

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

Question 12

What are the benefits of NIPS and NIPT?

Answer 12

Less invasive tests
No increased risk of miscarriage
Less expertise required to perform
Result can be obtained earlier

Question 13

What is chorionic villus sampling?

Answer 13

11-14 weeks
1-2% risk of miscarriage
Transabdominal or transvaginal
Takes sample of chorionic villi

Question 14

What is amniocentesis?

Answer 14

From 16 weeks
Sample of amniotic fluid
1% of miscarriage

Question 15

What tests are done with the samples?

Answer 15

Test for genetic disorder in question
Karyotype if chromosomal abnormality in family
PCR for all

Question 16

What is CGH array?

Answer 16

After concerns on 20 week scan
Looks for small imbalances in chromosomes
If something is found parents are tested

Question 17

What is the process of CGH array?

Answer 17

Extract and label DNA
Hybridise and wash
Scan
Analyse data

Question 18

What is trio exome?

Answer 18

Consider where foetus in previous pregnancy had significant anomalies
Exome is coding region of genes

Question 19

What are other options for a couple other than prenatal diagnosis?

Answer 19

No prenatal testing 
Use of egg/ sperm donors
Adoption
Choose not to have children 
Pre-implantation genetic diagnosis

Question 20

What are the two steps of adoption?

Answer 20

Registration and checks
Assessment and approval
Lengthy process

Question 21

What are the steps of PGD?

Answer 21

Stimulation of ovaries
Egg collection
Insemination
Fertilisation
Embryo biopsy
Embryo testing 
Embryo transfer
Pregnancy test

Question 22

What has to be thought about when facilitating decision making?

Answer 22

Previous experience
Family situation 
Religion
Personal beliefs
Psychosocial situation
Balancing miscarriage with genetic risks