Genetic Testing Flashcards
When does the nuchal scan take place and what happens?
10- 14 weeks gestation: booking bloods, hormone levels and scan where stenographer looks at nuchal fold (measure of baby’s neck) and take into account maternal age
Risk factor for Down’s syndrome calculated
What are the limits on risk?
Risk of 150 or higher is high, below 50 is low risk
What is the main method of pre-natal diagnosis of foetal abnormalities?
Ultrasound
All pregnant woman offered a scan at 12 weeks and anomaly scan at 20 weeks- in this scan you can see limbs and organs
What occurs in a normal pregnancy?
- Positive pregnancy test
- Book into antenatal care- see midwife
- Nuchal Scan
- Mid trimester anomaly scan
- Ultrasound at 11-14 and 20-22 weeks
What are the aims of the 12 weeks scan?
Date pregnancy accurately Diagnose multiple pregnancy Diagnose major foetal abnormalities Diagnose early miscarriage Assess risks of downs syndrome and other chromosomal abnormalities
What is nuchal translucency?
Measured at 10-14 weeks
It is the thickness of fluid at back of foetal neck
Increased more than 3mm can indicate:
-chromosomal abnormalities (NT and maternal age detects to 75% of downs syndrome)
-Birth defects (cardiac abnormalities, pulmonary, renal and abdominal wall defects)
-skeletal dysplasias
When is prenatal testing arranged?
Following abnormal findings at nuchal scan or mid trimester scan
Following result of combined test which gives increased risk of downs syndrome
If previous pregnancy affected with a condition
If parents are a carrier of chromosome rearrangement or genetic condition
Family history of genetic condition
What are aims of prenatal testing?
To inform and prepare parents for birth of affected baby
To allow in utero treatment
Manage the remainder of the pregnancy
To be prepaired for complications after birth
To allow termination of an affected foetus
What does a foetal MRI scan allow?
Allows you to look at organs more closely
What does a foetal cardiac scan allow you to do?
Allows you to see flow of blood through baby’s heart to diagnose cardiac conditions
How is testing done through cell free foetal DNA?
Non-invasive prenatal diagnosis (NIPD) works by analysing DNA fragments present in maternal plasma during pregnancy (cell free DNA)
Most DNA comes from mother
Cell free foetal DNA (cffDNA) is detectable form ~4-5 weeks gestation but cant be accurately detected until ~9 weeks
How is NIPD carried out?
At 9 weeks of gestation you take large sample of blood from mother
Testing is free for achondroplasia, thanatophoric dysplasia and aport syndrome
NIPD has been used for sexing
Sexing is offered when theres an X-linked condition in the family e.g. DMD
Test detects SRY gene on Y chromosome allowing us to enable if its a male or female foetus
If Male - go on to invasive prenatal test
If female- no invasive test required
When can NIPD be used?
Autosomal dominant single gene disorders inherited from father or arise de novo
NIPD can be used for recessive conditions where parents have different mutations- test detects paternal mutation
If the foetus has inherited paternal mutation, invasive prenatal testing can be offered
How is NIPD used for cystic fibrosis?
Haplotyping can test for both paternal and maternal mutations
How is cffDNA offered for aneuploidy?
Offered prenatal (Harmony) or via research studies- NIPT Harmony tests for T13, T18 and T21
