Genetic Screening Flashcards
What are the primary screening tests for chromosomal anomalies in the first trimester?
Combined first-trimester screening (nuchal translucency + serum biomarkers) and cell-free fetal DNA (cfDNA) testing.
What biomarkers are measured in first-trimester combined screening?
Beta-hCG (↑ in trisomy 21), PAPP-A (↓ in trisomy 21 and 18).
What is the significance of nuchal translucency (NT) measurement in the first trimester?
Increased NT (>3 mm) suggests risk for aneuploidy (trisomy 21, 18, 13) or congenital heart defects.
What screening test has the highest sensitivity for detecting trisomy 21?
Cell-free fetal DNA (cfDNA) testing (99% detection rate).
When is cell-free fetal DNA (cfDNA) testing recommended?
For high-risk pregnancies (advanced maternal age, abnormal ultrasound, previous trisomy pregnancy).
What are the primary second-trimester screening tests for chromosomal anomalies?
Quad screen and second-trimester ultrasound.
What biomarkers are assessed in the quad screen?
AFP (↓ in trisomy 21, ↑ in NTDs), hCG (↑ in trisomy 21), estriol (↓ in trisomy 21 & 18), inhibin A (↑ in trisomy 21).
What is the role of the quad screen in detecting neural tube defects (NTDs)?
Elevated AFP suggests an increased risk for NTDs.
What conditions are associated with a thickened nuchal fold in the second trimester?
Trisomy 21, Turner syndrome, congenital heart defects.
What are confirmatory tests for abnormal prenatal screening results?
Chorionic villus sampling (CVS, 10–14 weeks) and amniocentesis (15–22 weeks).
When is amniocentesis preferred over chorionic villus sampling?
After 15 weeks; lower risk of complications than CVS and allows AFP measurement for NTD screening.
What ultrasound findings suggest a neural tube defect (NTD)?
Absent cranial vault (anencephaly), lemon sign, banana sign, open spinal defect.
When is an ultrasound typically performed for fetal anatomy evaluation?
Between 18–22 weeks.
What is the benefit of integrated and sequential screening?
Combines first and second-trimester markers to improve sensitivity for aneuploidy.
