Prenatal Diagnosis Flashcards
1
Q
prenatal diagnosis
A
- medical evaluation of a fetus that provides both physical and genetic information
- genetic testing has the capability to diagnose fetal disease
- prior to testing, parents should be counseled about the reasons to do the test and possible outcomes
- depending on type of test, there could be risk to mom and pregnancy
2
Q
indications for prenatal diagnosis-inherited
A
- familial chromosome anomaly
- family hx of genetic disorder for which testing is available
- familial X linked recessive disorder without testing available
- increased risk of open neural tube defect (recurrence risk of 2-5%)
- carrier of genetic disorder, ethnic risk
- consanguinity
3
Q
other indications for prenatal diagnosis
A
- US anomaly
- repeated miscarriages
- abnormal MSAFP
- anxiety
- environmental exposures
- increased risk of chromosomal abnormality
4
Q
relative freq of types of aberration in chromosomally abnormal abortuses- mothers of all ages
A
- trisomies, 16 most common aborted
- 45X
- triploid
- tetraploid
- unbalanced translocation
5
Q
spontaneous termination freq
A
- 95% of 45X conceptions
- 90% of trisomy 13 conceptions
- 80% of trisomy 18 conceptions
- 65% of trisomy 21 conceptions
6
Q
types of tests available
A
non-invasive: -examination -US invasive: -cytogenetics -biochemical -molecular studies
7
Q
invasive vs non invasive
A
- in general, non invasive is better, less risk ot fetus
- want the most specific info at least risk
- type of testing performed depends on clinical indication- and what info needs to be collected
8
Q
US
A
- verify viability
- detect multiple pregnancy
- determine gestational age
- determine the sex
- identify possible abnormalities
- may indicate that additional studies are needed
- nuchal translucency- may be associated with chromosome abnormality- 6.0 mm for Down Syndrome
- unilateral or bilateral cleft lip/ palate or both
- neural tube defects (meningomyelocele)
9
Q
maternal serum alphafetoprotein
A
- 15-20 weeks
- high, low, normal
- gestational age
- mother’s weight, race, diabetic status
- albumin like protein produced in fetal liver
- if bigger mother, more volume, less AFP might be normal
- screening test for risk assessment
- low levels-down syndrome and other chromosome anomalies
- high levels- ONTD
- hard to interpret though
10
Q
maternal serum quad test
A
- AFP low
- hCG high
- unconjugated estriol (uE3) low
- dimeric inhibin A high
- 80% combined detection for DS
- 60% for 40 years
11
Q
integrated prenatal testing
A
- 10-13 weeks gestaion
- PAPP-A (preg associated plasma protein A, when low, inc risk of DS)
- nuchal translucency
- 15-21 weeks gestatoin the Quad MSAFP testing
12
Q
non-invasive prenatal screening/testing
NIPS/NIPT
A
- newest non invasive assay
- 4 commercial companies
13
Q
cffDNA
A
- cell free fetal/placental DNA
- isolated from maternal blood at 10-22 weeks
- 10-15% of cfDNA in maternal blood is fetal origin
14
Q
technology
A
- sequencing to identify DNA fragments
- determine chromosomal source of each fragment
- statistically analyze the number of fragments per chromosome compared to expected number for mother and fetus
- then use software to evaluate data
- expected amounts of DNA per chromosome are analyzed, increase or decrease suggests aneuploidy
- screening test for risk, has to be confirmed
15
Q
NIPS accuracy
A
- DS and trisomy 18 99%, false pos of 0.2%
- trisomy 13- 72-92%, false pos 1%
- XX 98.4%
- XY 99%
- abnormals should be confirmed
- 0.5-7% failure rate- due to not enough DNA
- but is better than serum screening
