Prenatal Diagnosis- Lecture 9/22/21 Flashcards
Screening
Gives a probability, not a definitive answer, provides individual risk assessment
Diagnostic
Definitive, procedure-related risk of pregnancy loss
Screening tests (3)
- Ultrasound
- Maternal serum marker screening
- Noninvasive prenatal testing (NIPT)
Diagnostic tests (2)
- Chorionic villus sampling
- Amniocentesis
Nuchal translucency US
Performed at 11-13 weeks
- Measures nuchal translucency, >3 mm associated with increased risk for aneuploidy and fetal heart defects
- Detects ~60% of fetus with aneuploidy
Fetal anatomic survey
- Usually 18-20 weeks gestation
-can detect structural fetal anomalies such as congenital heart defect
Can detect soft markers for aneuploidy
Fetal anatomic survey findings
~90-95% of open neural tube defects
~80% of congenital heart defects
~50% of fetuses with Down syndrome have a US finding
~80% of fetuses with trisomy 18 have at least one US finding
Positive predictive value
The chance a positive result is a true positive
Maternal serum marker screening
Routine blood testing offered to all pregnant people
Can evaluate the. Chances for Down syndrome, trisomy 18, and open neural tube defects
Screen positive is 1/200 or higher
Indications for additional testing (6)
- Advanced maternal age
- Fetal ultrasound findings
- Prior pregnancy with aneuploidy
- parental chromosome translocation
- positive maternal serum screening results
- Positive non-invasive prenatal testing results
NIPT
Evaluation of cell-free DNA in maternal serum, can be performed after 10 weeks gestation
NIPT detection rates
99% detection rate for T21
Chorionic villus sampling
10-13 weeks, take sample from chorionic villus
Amniocentesis
15+ weeks, risk of miscarriage, detects neural tube defects
