Prenatal Diagnosis Flashcards
Genetic screening includes asking about
Maternal age
Family history
Ethnic background
Specific-directed questioning: have you ever had a child w ..
___% of first trimester losses are the result of chromosomal abnormalities
50
__% of couples of recurrent miscarriages have a balanced chromosomal translocation
3
___% of stillborns and ___% of liveborns have a chromosomal abnormality
7% and 0.5% have a chromosomal abnormality
Maternal Serum Alpha-Fetoprotein
what is it? clinical significanec?
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
Baby has a neural tube defect. What do we expect to see in the mother?
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.
Quadruple screen
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!!
What is positive predictive value and detection sensitivity?
Pretty low for down, trisomy 18, and open NTD
dont need to memorize these numbers
Fetal DNA in maternal blood (i.e. cell-free DNA testing)
clinical significance
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
cell free DNA in maternal blood is a mix of __ and ___ DNA
maternal and placental DNA
When should you test for fetal DNA in matenral blood/ cell-free DNA testing?
prob low yield
Old mom
Abnormal ultrasound
Abnormal screens (e.g. quad screen)
family history of trisomy
summary for fetal trisomy screenings
Techniques to obtain fetal samples
Amniocentesis
Chorionic villus sampling (CVS)
Fetal blood sampleing: sample from from umbilical vein, but low yield
Amniocentesis
Sampling amniotic fluid for AFP, karyotype, enzyme analysis, etc
Can analyze isoenzymes of acetylcholineesterase specific to neural tissue to screen for NTDs
Chorionic villus sampling
Collect a placental sample through the abdomen of vagina
What is this characteristic of
Clenched hands
trisomy 18
Short fingers & hypoplastic 5th finger
Transverse palmar crease (not seen on ultrasound tho)
Trisomy 21
The bottom baby has
flat face= trisomy21
Brain cysts are characteristic of
trisomy 18
Double bubble sign
Duodenal atresia -> test for trisomy 21
nuchal folds/ nuchal translucency
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
