Prenatal Testing

Question 1

how many babies are born with genetic defects (including stillbirths >20 weeks gestation). These tend to be […] disorders, of […] gene defects.

Answer 1

4% inherited single gene defects

Question 2

the most common chromosomal mutations that reach term are?

Answer 2

trisomy 21 (downs syndrome) and XXY (klinefelter’s)

Question 3

taking a good family history is very important in determining risk of genetic defects. Ideally a […] generation history is ideal.

Answer 3

three generation history.

Question 4

relationship between maternal age and risk of downs syndrome?

Answer 4

increases exponentially after 30….

Question 5

what types of prenatal testing are available to expecting mothers?

Answer 5

screening tests are offered to all mothers and non invasive

diagnostic tests are offered to mothers at higher risk of genetic disorder and are somewhat invasive

NB: prenatal tests are not definitive.

Question 6

1 in 500 births suffers from a neural tube defect, this can be prevented by taking […..] in anticipation of and during pregnancy.

Answer 6

folate supplement

Question 7

what does 1st Trimester combined screening consist of?

Answer 7

screens for t21 and t18

1. blood test for 2 biochemical analytes at 10wks
2. ultrasound at 11-13 wks to measure crown rump length and nuchal translucency. (shape of nasal bone can also be a marker for trisomy 21)

Question 8

what does 2nd trimester maternal serum screening involve?

Answer 8

Screens for T21 (85% detection rate), T18, and neural tube defects (93% detection).

1. maternal blood tested at 15-17 wks, tested for presence of 4 analytes.

factored into predictive model with maternal age to calculate risk figure.

Question 9

What does the new NIPT/S test involve?

Answer 9

screens for fetal DNA fragments in maternal blood. fragments are sequenced and compared against a normal reference for analysis.

non invasive and available at 10 wks gestation.

Question 10

if a woman is found to be at increased risk, she could be offered prenatal diagnostic tests, which would involve…..

Answer 10

fetal anomaly ultrasound and/or invasive diagnostic testing (amniocentesis, CVS)

samples undergo FISH/PCR analysis for T21, T13, T18, X and Y and karyotyping.

(+ DNA analysis for carrier couple).

CVS (chorionic villus sampling) at 11 weeks, and Amniocentesis at 15-16 wks.

NB: slightly greater risk of miscarriage with CVS.

Question 11

how does chromosomal microarrays (molecular karyotyping) work?

Answer 11

patient sample labelled with red fluorescent dye mixed with normal sample labelled green dye, mixed together, and scanned to show deletions and duplications.

Question 12

how should molecular karyotyping results be interpreted?

Answer 12

Question 13

now that youre such hot shit, describe the spectrum of prenatal testing available to expecting mothers?

Answer 13

Question 14

sometimes family history wont reveal a genetic defect risk because many of these are recessive defects. However, In order to take a good history, what questions should you ask

Answer 14