Prenatal Genetics & Reproductive Options Flashcards

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

Answer: AFP, hCG, unconjugated estriol, and inhibin A

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

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

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

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

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

Answer: Chorionic villus sampling (CVS)

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

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

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

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

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

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

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

A patient presents at 14 weeks gestation after a CVS revealed trisomy 21 in the fetus. The genetic counselor should provide counseling that includes:

Answer: Balanced information about the condition, reproductive options, and support resources

Nondirective counseling requires presenting balanced, comprehensive information about the diagnosis, all options, and available support without bias.