Prenatal Diagnosis of Genetic Disease Flashcards
What are the scans offered for a normal pregnancy?
positive pregnancy test booked into antenatal care Nuchal scan –10-14 weeks Mid-trimester anomaly scan All pregnant women should be offered ultrasound scans at 20-22 weeks as well
when is pre natal testing arranged?
- Following abnormal findings at nuchal or mid-trimester scan - results of combined test, which give an increased risk of Down Syndrome. - If the parent(s) is a carrier of chromosome rearrangement or genetic condition - Family History of genetic condition
what are the aims of pre natal testing?
- To inform and prepare parents for the birth of an affected child - In utero treatment could be offered - Aids management of the rest of the pregnancy - To allow TERMINATION of an affected foetus
When is a nuchal scan offered and what is it used to determine?
12 weeks Date the pregnancy Multiple pregnancies Major foetal abnormalities Early miscarriage Risk of chromosomal abnormalities done by looking at the nuchal translucency (fluid at the back of the babys head)
What is considered an abnormal nuchal translucency and what would such a result suggest?
nuchal translucency is usually below 3.5mm Greater than 3mm – indicates possibility of: Chromosomal abnormalities ( downs, pataeu, turner, edwards) Birth defects cardiac, pulmonary, renal 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, cell free foetal DNA) - Invasive (chorionic villus sampling, amniocentesis)
What can ultrasound tests be used for?
Nuchal translucency Nasal bone Dating scan from 9 weeks
(non invasive) what does the foetal MRI show?
-20+ weeks - High-level anomaly scan can be diagnostic - showing cleft lip, limb deformity or cardiac problem. - soft markers for other problems.
(non invasive) Nasal Bone ?
- presence or absence can indicate Down Syndrome. - looking at the Nasal Bone increases the sensitivity of DS screening
Foetal Cardiac Scans ?
can show cardiac problems - only done if the other scans indicate potential problem
(minimally invasive) when is maternal serum screening done?
- 11-14 weeks AND 16-20 weeks - tests involve blood tests for the mum so there is no risk to the foetus Detects increased risk of trisomy 21, trisomy 18 and/or neural tube defects.
What does maternal serum screening look for?
11-14 weeks = looks for presence of hCG and PAPP A 16-20 weeks = looks for presence of hCG, PAPP A, AFP and uE3 - Nuchal Translucency Measurement - 11-14 weeks - If these tests find that the woman is at high risk of some genetic diseases, she will be offered more invasive prenatal tests
In what situation is cell-free foetal DNA testing offered? what does it look for
Offered in particular if the baby has a chance of having an X-linked condition - only boys can be affected and girls can be carriers - test is done to determine the sex of the baby -A small amount of Foetal DNA will be in the maternal blood - the DNA is isolated and the presence of the Y chromosome is detected if present - If the Y chromosome is present, you know the baby is male - 9 weeks
What is cffDNA used to determine?
- The sex of the baby (looks for the presence of the SRY gene) on the Y chromosome to see if baby is male or female - looks for sex linked conditions (males need further tests)
how does cffDNA test for aneuploidy?
- offered privately - Tests for T13, T18 and T21 - not 100% accurate therefore not on the NHS
