Prenatal Diagnosis

Question 1

Genetic screening includes asking about

Answer 1

Maternal age

Family history

Ethnic background

Specific-directed questioning: have you ever had a child w ..

Question 2

___% of first trimester losses are the result of chromosomal abnormalities

Answer 2

50

Question 3

__% of couples of recurrent miscarriages have a balanced chromosomal translocation

Answer 3

3

Question 4

___% of stillborns and ___% of liveborns have a chromosomal abnormality

Answer 4

7% and 0.5% have a chromosomal abnormality

Question 5

Maternal Serum Alpha-Fetoprotein

what is it? clinical significanec?

Answer 5

a fetal variant of albumin

Can leak into amniotic fluid when the fetus has an open neural tube defect (e.g. anencephaly); high levels of amniotic fluid –> high levels in mother’s blood

Question 6

Baby has a neural tube defect. What do we expect to see in the mother?

Answer 6

feto alpha protein in the mothers blood

Prevention of NTD: all women should take 400 ug folic acid one month prior to pregnancy because the neural tube closes at 6 menstrual weeks.

Question 7

Quadruple screen

Answer 7

Tests maternal serum at ~15-20wks of gestation for…

AFP

Estriols

bHcG

Inhibin A

However, accurate gestational age is essential or else it will look weird!!

Question 8

What is positive predictive value and detection sensitivity?

Answer 8

Pretty low for down, trisomy 18, and open NTD

dont need to memorize these numbers

Question 9

Fetal DNA in maternal blood (i.e. cell-free DNA testing)

clinical significance

Answer 9

High sensitivity (99%) for trisomy 21 & 18

Adequate detection (92% sensitive) of trisomy 13

• Done 10 wks after gestation
• False positive & false negatives are very low

Question 10

cell free DNA in maternal blood is a mix of __ and ___ DNA

Answer 10

maternal and placental DNA

Question 11

When should you test for fetal DNA in matenral blood/ cell-free DNA testing?

prob low yield

Answer 11

Old mom

Abnormal ultrasound

Abnormal screens (e.g. quad screen)

family history of trisomy

Question 12

summary for fetal trisomy screenings

Question 13

Techniques to obtain fetal samples

Answer 13

Amniocentesis

Chorionic villus sampling (CVS)

Fetal blood sampleing: sample from from umbilical vein, but low yield

Question 14

Amniocentesis

Answer 14

Sampling amniotic fluid for AFP, karyotype, enzyme analysis, etc

Can analyze isoenzymes of acetylcholineesterase specific to neural tissue to screen for NTDs

Question 15

Chorionic villus sampling

Answer 15

Collect a placental sample through the abdomen of vagina

Question 16

What is this characteristic of

Answer 16

Clenched hands

trisomy 18

Question 17

Answer 17

Short fingers & hypoplastic 5th finger

Transverse palmar crease (not seen on ultrasound tho)

Trisomy 21

Question 18

The bottom baby has

Answer 18

flat face= trisomy21

Question 19

Brain cysts are characteristic of

Answer 19

trisomy 18

Question 20

Double bubble sign

Answer 20

Duodenal atresia -> test for trisomy 21

Question 21

nuchal folds/ nuchal translucency

Answer 21

Detects fluid under the skin behind the fetal neck via ultrasound

fluid=black, bone =white

increased risk of chromosome abnormalities: trisomies 21, 18, 13, turner syndrome, etc