CGC Prenatal Genetics & Reproductive Options 3

Question 1

The quad screen (maternal serum analytes) is a second-trimester screening test that includes which analytes?

Accepted Answer

AFP, hCG, unconjugated estriol, and inhibin A

Answer

The quad screen measures AFP, hCG, unconjugated estriol (uE3), and inhibin A to screen for trisomies 21, 18, and neural tube defects.

Question 2

A patient is found to have a fetus with a de novo pathogenic variant identified on exome sequencing. 'De novo' means:

Accepted Answer

The variant arose newly in the fetus and is not present in either parent

Answer

De novo variants arise spontaneously in the germline or early development and are absent in both biological parents.

Question 3

Confined placental mosaicism (CPM) is a limitation unique to which prenatal diagnostic procedure?

Accepted Answer

Chorionic villus sampling (CVS)

Answer

CPM occurs in CVS because placental cells (trophoblast) may carry chromosomal abnormalities not present in the fetus, leading to false-positive results.

Question 4

A patient asks about the difference between a 'screen positive' and a 'diagnostic positive' result for Down syndrome. The counselor correctly explains that:

Accepted Answer

A screen positive indicates increased risk but requires diagnostic confirmation; a diagnostic positive confirms the diagnosis

Answer

Screening identifies individuals at increased risk who need diagnostic testing, while diagnostic testing provides definitive chromosomal confirmation.

Question 5

Chromosomal microarray analysis (CMA) in the prenatal setting has advantages over karyotype because it can detect:

Accepted Answer

Submicroscopic copy number variants (CNVs) not visible by standard karyotype

Answer

CMA detects small CNVs (deletions and duplications) at a higher resolution than karyotype but does not detect single-nucleotide variants or repeat expansions.

CGC - Certified Genetic Counselor Practice Test

CGC - Certified Genetic Counselor Practice Test

CGC Prenatal Genetics & Reproductive Options 3