prenatal diagnosis of genetic diseases

Question 1

non-invasive tests

Answer 1

ultrasound, MRI, NIPD

Question 2

ultrasound

Answer 2

early/dating scan; nuchal translucency and nasal bone (Down); high level/anomaly scan

Question 3

MRI

Answer 3

high level/anomaly scan can be diagnostic; show soft markers for other problems; nasal bone=>increase sensitivity to Down screening; foetal cardiac scans

Question 4

non-invasive prenatal testing (NIPD) with cell-free foetal DNA (cffDNA): purpose

Answer 4

conducted especially if chance of X-linked condition; determines sex of baby (foetal DNA in maternal blood can isolate DNA and look for (SR)Y chromosome); tests for aneuploidy and some autosomal dominant monogenic diseases

Question 5

non-invasive prenatal testing (NIPD) with cell-free foetal DNA (cffDNA): advantages

Answer 5

reduce no. invasive tests; no risk miscarriage; offered early

Question 6

non-invasive prenatal testing (NIPD) with cell-free foetal DNA (cffDNA): disadvantages

Answer 6

if multiple pregnancies, cannot tell which foetus DNA is from unless identical twins; if mother has high BMI, relative proportion of foetal DNA is lower; ethical issues; invasive test may still be needed

Question 7

minimally invasive maternal serum screening

Answer 7

blood test to mum; detects increased risk of trisomy 21, 17 or neural tube defects; 1st and 2nd trimesters

Question 8

when are invasive tests done

Answer 8

when known risk shown by prenatal testing and if known genetic condition in family (have QF-PCR test for trisomy 13, 18 and 21); carry miscarriage risk

Question 9

invasive tests

Answer 9

chorionic villus sampling (CVS), amniocentesis, foetal blood sampling

Question 10

chorionic villus sampling (CVS)

Answer 10

11-14 weeks; 1-2% chance miscarriage; abdomen/vagina; part of developing placenta has same DNA as foetus; tertiary referral centre

Question 11

amniocentesis

Answer 11

16 weeks; requires ultrasound; amniotic fluid sample with foetal cells via needle puncture through maternal abdomen and amniotic membranes; 1% chance miscarriage

Question 12

foetal blood sampling

Answer 12

assesses foetal anaemia