Prenatal Genetics 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 the possible outcomes
- depending on the type of test, there could be a risk to the mom and to the pregnancy
2
Q
Indications for Prenatal Diagnosis-Inherited
A
- familial chromosome anomaly
- family history of a genetic disorder for which testing is available
- Familial X linked recessive disorder without testing available
- increased risk of ONTD (recurrence risk 2-5%)
- carrier of genetic disorder, ethnic risk
- consanguinity
3
Q
Other Reasons for Prenatal Diagnosis
A
- ultrasound anomaly
- repeated miscarriages
- Abnormal MSAFP (maternal serum alphafetoprotein)
- anxiety
- environmental exposures
- increased risk of a chromosomal abnormality
4
Q
Relative Frequency of Types of Aberration
A
- most common live birth anomaly is trisomy 21
- most common aneuploidy is 45,X
- most common autosomal aneuploidy is trisomy 16
- triploidy is the third highest frequency cause of fetal loss
5
Q
Spontaneous termination frequencies
A
- 95% of 45,X conceptions
- 90% of trisomy 12 conceptions
- 80% of trisomy 18 conceptions
- 65% of trisomy 21 conceptions
6
Q
Tests available
A
- examination
- ultrasound
- cytogenetics
- biochemical
- molecular studies
7
Q
invasive vs non-invasive tests
A
- in general, non-invasive is better than invasive- less risk to the fetus
- want the most specific information at the least risk
- types of testing performed depends on clinical indication- and what information needs to be collected
8
Q
Ultrasound
A
- verify viability
- detect a multiple pregnancy
- determines the gestational age
- determine the sex
- identify possible abnormalities
- may indicate that additional studies are needed
- usually performed around 18 weeks
9
Q
Nuchal translucency
A
- indicator on ultrasound of a possible abnormality in a fetus like chromosomal
- thickness of 6.0 mm has been associated with Down syndrome
10
Q
Clefting
A
-unilateral or bilateral cleft lip, cleft palate, or both can be detected on ultrasound and are usually indicators of a genetic defect
11
Q
Neural tube defects
A
- can be detected on ultrasounds
- like a meningomyelocele
- range of severity
- less severe forms may be corrected surgically, more severe can be debilitating
- closed: skin is intact
- open: rupture in the skin (spinal fluid mix with amniotic fluid)
- severe ones like anencephaly- absence of the brain and is lethal
- encephalocele when the brain is extruded from the skull
12
Q
Maternal Serum Alphafetoprotein
A
- 15-20 weeks
- high, low, normal
- gestational age
- mother’s weight, race, diabetic status
- produced by fetal liver and crosses the placenta and can be detected in maternal circulation
- AFP is correlated to the stage of gestation
- risk assessment
- low levels: Down syndrome
- high levels: ONTD- open tubular defects
13
Q
Maternal Serum Quad Test
A
- 4 different substances
- alpha fetoprotein low
- hCG up
- unconjugated estrol low
- dimeric inhibin up
- 80% combined detection for DS
- can be used up to 40 years
14
Q
Integrated Prenatal Testing
A
- 10-13 weeks gestation:
- PAPP-A (pregnancy-associated plasma protein A, when lower associated with increased risk of DS)
- nuchal translucency
- 15-21 weeks gestation the Quad MSAFP testing is performed
15
Q
Non-invasive Prenatal Screening/Testing
A
- the newst non-invasive assay is know as NIPS
- cffDNA= cell free fetal/placental DNA
- isolated from maternal blood at 10-22 weeks gestation
- 10-15% of cfDNA in maternal blood is fetal in origin
