Prenatal Diagnosis of Genetic Diseases Flashcards
What are the scans offered for a normal pregnancy?
Nuchal scan –11-14 weeks
Mid-trimester anomaly scan All pregnant women should be offered ultrasound scans at 20-22 weeks as well
When is a nuchal scan offered and what is it used to determine?
12 weeks Date the pregnancy Diagnose Multiple pregnancies Diagnose Major foetal abnormalities Diagnose Early miscarriage assess Risk of chromosomal abnormalities and Down syndrome.
When is a nuchal translucency offered and what is considered abnormal and what does this indicate?
-10-14 weeks
-Greater than 3mm (is a collection of fluid under the skin at the back of your baby’s neck)
– indicates possibility of: Chromosomal abnormalities Birth defects,Skeletal dysplasia
What are the three types of prenatal testing and which test fall under each category?
Non-invasive;
-Ultrasound/MRI
Minimally invasive:
- Maternal serum screening:is a blood test offered to pregnant women that helps determine the risk of Down syndrome
- cell free foetal DNA
Invasive;
- Chorionic Villus Sampling (CVS)
- Amniocentesis
What can ultrasound tests be used for?
Nuchal translucency & Nasal bone presence or absence can indicate
Down syndrome
High level/ anomaly e.g. cleft lip, limb deformity or cardiac problem.
early/dating scan
When is maternal serum screening done?
11-14 weeks AND 16-20 weeks
What does maternal serum screening look for?
11-14 weeks = looks for presence of hCG( human chorionic gonadotrophin) and PAPP A( pregnancy associated plasma protein A) 16-20 weeks = looks for presence of hCG, PAPP A, AFP (alpha foetal protein) and uE3 (oestriol)
In what situation is cell-free foetal DNA testing offered?
Offered in particular if the baby has a chance of having an X-linked condition
What is cffDNA used to determine?
What private cffDNA is used to test for
The sex of the baby (looks for the presence of the SRY gene)
Private:
-Harmony test
Tests for T13,T18,T21
What does the cfDNA consist and what is different if someone has down’s syndrome?
DNA from the mother and fetus.
In trisomy 21 the amount of cfDNA for chromosome 21 is higher than in normal pregnancies.
What free NIPD does the NHS do and the private NIPD?
FREE
Achondroplasia -
Thanatophoric dysplasia -
Apert syndrome
PRIVATE
Autosomal dominant single gene disorders inherited from the father or arise de novo
What are the limitations of NIPD and NIPT?
Multiple pregnancies – cannot tell which foetus the DNA is from High BMI – relative proportions of cffDNA is reduced in obese women Ethical issues
What are the benefits of NIPD (Non-invasive prenatal diagnosis/testing) and NIPT?
No risk of miscarriage Reduces the need for more invasive testing
-in many cases NIPD/NIPT can be done earlier than traditional invasive testing- so getting results earlier
What is the problem with invasive prenatal testing?
Small risk of miscarriage (both)
Amniocentesis: infection and Rh sensitisation
What is CVS and when is it done?
Chorionic villus sampling – take a sample from the chorionic villus which is part of developing placenta and this has the same genetic material as the fetus
11-14 weeks
-done trans abdominal or trans vaginal
earlier than amniocentesis which is important for many patients if deciding for termination
