5. Prenatal Diagnosis of Genetic Disease Flashcards
(39 cards)
What are the scans offered for a normal pregnancy?
Nuchal scan: 10-14 weeks
Mid-trimester anomaly scan: 20 weeks
Offered ultrasound scans at 11-14 and 20-22 weeks
What is the main method for prenatal diagnosis of foetal defects?
Ultrasound
When is a nuchal scan offered and what is it used to determine?
12 weeks
Date pregnancy
Diagnose multiple pregnancies (twins/ triplets)
Major Foetal Abnormalities
Diagnose early miscarriage
Assess risks of Down Syndrome (DS) and other chromosomal abnormalities
What is considered an abnormal nuchal translucency and what would such a result suggest?
> 3mm
Indicates possibility of:
Chromosomal abnormalities
Birth defects
How is risk of downs syndrome assessed in nuchal scan?
Look at thickness of NT Assess: maternal age hormone levels nasal bone foetal abnormalities
What birth defects may be identified from nuchal translucency?
Cardiac anomalies Pulmonary defects (diaphragmatic hernia) Renal defects Abdominal wall defects Skeletal dysplasia’s
Why must further tests be taken after nuchal translucency?
NT is a screening test
NT is NOT diagnostic
When is prenatal testing arranged?
After abnormal findings at nuchal/ mid-trimester scan
After results of combined test which give an increased risk of DS
If previous pregnancy affected with a condition e.g. DS
If parent(s) carrier of chromosome rearrangement or genetic condition, e.g. t(13;14), Duchenne Muscular Dystrophy, Huntingdon’s Disease
FH of genetic condition
What are the aims of prenatal testing?
Inform and prepare parents for the birth of an affected baby
Allow in utero treatment
Manage remainder of pregnancy
Be prepared for complications at or after birth
Allow termination of an affected fetus
What are the 3 types of prenatal testing and which test fall under each category?
Scanning (ultrasound, MRI)
Non- invasive (maternal serum screening, cell free foetal DNA)
Invasive (chorionic villus sampling, amniocentesis)
What can the early ultrasound test be used for?
Dating
Nuchal translucency
Nasal bone
What can the anomaly ultrasound test be used for?
Higher detail
Indications of abnormalities that might need treatment
When are MRI tests performed and what is the purpose?
20 weeks+
Show how brain and heart are developing- indicates need for test for CF
What does maternal serum screening test for?
maternal serum markers in blood to detect increased risk of fetal trisomy 21, trisomy 18 and/or neural tube defects
Looks at hormones in maternal serum
When is maternal serum screening done?
11-14 weeks AND 16-20 weeks
What is indicated if at the 12 week maternal serum screening hCG is high and PAPP A is low?
Down syndrome
What does maternal serum screening look for?
11-14 weeks = presence of hCG and PAPP A
16-20 weeks = presence of hCG, PAPP A, AFP and uE3
In what situation is cell-free foetal DNA testing offered?
Offered when there is a X-linked condition in the family e.g. DMD
Or privately via NHS
What is cffDNA used to determine?
The sex of the baby
(looks for the presence of the SRY gene)
If male: go to prenatal test
If female: no invasive test required
What is NIPD?
Non-invasive prenatal diagnosis
How does NIPD work?
Analyses DNA fragments present in maternal plasma during pregnancy (cell-free DNA).
What are the limitations of NIPD and NIPT?
Multiple pregnancies – can’t tell which foetus DNA is from
High BMI – relative proportions of cffDNA is reduced in obese women
Ethical issues: may not prepare themselves for same implications as an invasive test
Invasive test may be required to confirm result
What are the benefits of NIPD and NIPT?
No increased risk of miscarriage
Reduces the need for more invasive testing
Less expertise required than for invasive test
Can offer testing earlier than invasive methods
When is invasive testing offered?
Offered if there is ‘known risk’
most accurate diagnosis, not just indication
