Preparatory Mindset

Study this chapter with focus on how genetic principles affect clinical practice.

Core Concepts

• Maternal serum screening: α-fetoprotein (AFP), hCG, estriol, inhibin A — detects risk of NTDs and aneuploidy


• Nuchal translucency: Ultrasound measurement of fetal nuchal fold thickness at 11-14 weeks — screens for Down syndrome


• Amniocentesis: Amniotic fluid sampling at 15-20 weeks → fetal karyotype, biochemical analysis


• Chorionic villus sampling (CVS) : Placental tissue sampling at 10-13 weeks → earlier result but higher miscarriage risk


• Non-invasive prenatal testing (NIPT) : Cell-free fetal DNA from maternal blood → screens for trisomy 13, 18, 21 (high sensitivity)


• Prenatal diagnosis indications: Advanced maternal age, abnormal screen, family history of genetic disorder, previous affected child

High-Yield Points

• Amniocentesis (15-20 wks) vs CVS (10-13 wks) vs NIPT (blood test, screening only)


• NIPT screens for trisomy 13, 18, 21 — very high sensitivity


• Maternal AFP: ↑ = neural tube defect; ↓ = Down syndrome risk

Topic Summary

Prenatal screening identifies pregnancies at risk; prenatal diagnosis confirms or excludes genetic disorders.