CGC Prenatal Genetics & Reproductive Options 1 — Questions and Answers
Question 1: Cell-free DNA (cfDNA) screening in pregnancy MOST accurately screens for which condition?
- Neural tube defects
- Trisomy 21 (Down syndrome) (Correct answer)
- Single-gene disorders such as cystic fibrosis
- Structural heart defects
Correct answer: Trisomy 21 (Down syndrome)
cfDNA screening has the highest sensitivity and specificity for trisomy 21 among common chromosomal aneuploidies.
Question 2: A patient with a positive cfDNA result for trisomy 18 should be counseled that:
- The result confirms the diagnosis and no further testing is needed
- Diagnostic confirmation via amniocentesis or CVS is recommended before clinical decisions are made (Correct answer)
- The fetus definitely has trisomy 18
- The test result is unreliable and should be repeated
Correct answer: Diagnostic confirmation via amniocentesis or CVS is recommended before clinical decisions are made
cfDNA is a screening test, not diagnostic; a positive result requires invasive diagnostic confirmation before clinical management decisions.
Question 3: The procedure-related pregnancy loss risk associated with amniocentesis is approximately:
- 1 in 10
- 1 in 100 to 1 in 200 (Correct answer)
- 1 in 1,000
- Less than 1 in 5,000
Correct answer: 1 in 100 to 1 in 200
Contemporary studies estimate the procedure-related loss rate for amniocentesis at approximately 1 in 100 to 1 in 200, though older estimates were higher.
Question 4: Chorionic villus sampling (CVS) is typically performed at which gestational age?
- 10–13 weeks (Correct answer)
- 15–20 weeks
- 22–24 weeks
- After 28 weeks
Correct answer: 10–13 weeks
CVS is performed in the first trimester between 10 and 13 weeks, providing earlier diagnostic results compared to amniocentesis.
Question 5: A patient of advanced maternal age asks about the risk of chromosomal abnormalities. The counselor explains that the baseline risk for trisomy 21 at age 35 is approximately:
- 1 in 50
- 1 in 385 (Correct answer)
- 1 in 1,000
- 1 in 2,000
Correct answer: 1 in 385
At age 35, the risk for trisomy 21 is approximately 1 in 385, which has historically defined the threshold for discussing invasive prenatal diagnosis.
Question 6: Preimplantation genetic testing for aneuploidy (PGT-A) is used to:
- Diagnose chromosomal abnormalities in an ongoing pregnancy
- Screen embryos created through IVF for chromosomal abnormalities before transfer (Correct answer)
- Predict the sex of a naturally conceived fetus
- Replace the need for prenatal diagnosis
Correct answer: Screen embryos created through IVF for chromosomal abnormalities before transfer
PGT-A screens IVF embryos for aneuploidy prior to uterine transfer to improve implantation success and reduce miscarriage risk.
CGC Prenatal Genetics & Reproductive Options 1
Cell-free DNA (cfDNA) screening in pregnancy MOST accurately screens for which condition?