Prenatal dx Flashcards
How to estimate gestational age in:
First trimester
Crown-rump length
(only useful in 1st trimester - cat curling up)
first trimester: 7 days
How to estimate gestational age in:
2nd+3rd
(beyond 12 weeks)
- Biparietal Diameter (BPD)
- Abdominal circumference (AC)
- Femur length (FL)
What is AFP?
Where is it made?
What: fetal albumin
Made: fetal liver
What do high +low levels of aFP mean?
High: 1. Most is NOT a NTD (mom has incorrect dating, and shes further along than expected) or 2. Maternal-fetal hemorrhage 3. Multiple gestations 4. NTD: Spina bifida, omphalocoele
Low: Down syndrome
% of reported chromosomal abnormalities
- Trisomy 21 (half)
- Other
- Trisomy 18
> 35 is considered advanced maternal age
Complications of DS
- Mental retardation
- Growth retardation
- Early alzheimers
- Congenital heart defects
- Hearing loss
- Ophthalmic disorders
hCG lvls elevated or low indicates?
Nl: NTD
High: Trisomy 21
Low:
Trisomy 18
Increased lvls of inhibin A indicates?
Trisomy 21
Low PAPP-A indicates?
Trisomy 13, 18, 21
Nuchal translucency testing indicates:
- what week is it measured at?
90% accurate for detecting Trisomy 21
98% accurate for detecting trisomy 18
- Nuchal translucency
Chorionic villus sampling detects: Samples \_\_\_: Completed at \_\_\_ weeks: Can it detect NTD? How is it beneficial to other sampling techniques?
Detects: genetic, metabolic, & DNA abnormalities
Samples developing placenta
Completed at 10-12 weeks
Can it detect NTD? No!
Earlier than amniocentesis
Non invasive test with no miscarriage risk
Cell free fetal DNA testing
- available early in gestation
Does massively parallel sequencing differentiate fetal vs maternal DNA?
NO!
But, Over-representation of chromosome 21 fragments in affected preg is significant.
Population based approach
- example
Screening for NTD or Down Syndrome
Specific population subgroups
- example
Thalassemia
Highly targeted screening example
Families known to be carriers of certain diseases/genes
- hemophilia
- cardiac defects
Cornerstones of prenatal dx
- Personal hx
- Family hx
- Non directive counseling
- Testing
Examples of Noninvasive tests
Blood draw
(Maternal serum analytes: look for markers)
Ultrasound
Invasive testing
- Examples
- Benefits and risk
Amniocentesis
Chorionic villus sampling (CVS)
- both:
- pose small risk to fetus
- Access to fetal cells: analyze chromosomal anomalies and single gene disorders
Indications for invasive dx diagnosis includes: (5)
- Advanced maternal age (>35 at due date)
- Positive aneuploidy screening test
- Abnl ultrasound finding
- anatomic
- IUGR
- amniotic fluid volume - Known parental chromosome rearrangements
- Previous affected child
When is nuchal translucency measured?
10-14 weeks gest., when fetal lymphatic system is developing and the placental resistance is high.
- after 14 weeks, the lymphatic system can drain excess fluid, and peripheral resistance of placenta falls.
(abnl fluid accumulation can go undetected)
What weeks can you evaluate internal organs and extremities for anatomic abnormalities at how many weeks gestation?
16-20 weeks gest.
- biparietal diam
- femur length
- abdom circ.
When can amniocentesis be performed?
When can CVS be performed?
AC: With ultrasound guidance btwn 14-20 weeks gest.
CVS: 9.5-12.5 weeks
