Flashcards in Prenatal Diagnosis of Genetic Disease Deck (17):
What are the scans offered for a normal pregnancy?
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 a nuchal scan offered and what is it used to determine?
Date the pregnancy
Major foetal abnormalities
Risk of chromosomal abnormalities
What is considered an abnormal nuchal translucency and what would such a result suggest?
Greater than 3mm – indicates possibility of: Chromosomal abnormalities
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?
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 and PAPP A
16-20 weeks = looks for presence of hCG, PAPP A, AFP and uE3
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?
The sex of the baby (looks for the presence of the SRY gene)
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 and NIPT?
No risk of miscarriage Reduces the need for more invasive testing
What is the problem with invasive prenatal testing?
Small risk of miscarriage
What is CVS and when is it done?
Chorionic villus sampling – take a sample from the chorionic villus which has the same genetic material as the foetus
What is amniocentesis and when is it done?
Taking a sample of amniotic fluid – 16+ weeks
What further tests are done to the DNA obtained via CVS or amniocentesis?
Karyotype QF-PCR (test for trisomies)
Describe pre-implantation genetic diagnosis.
IVF is used to produce a zygote
A cell is sampled at the 8-cell stage and tested to identify any genetic defects Only the cells with no genetic defects will be implanted