Which prenatal test provides diagnostic confirmation for Down syndrome by sampling fetal tissue?

• A. Amniocentesis
• B. Ultrasound
• C. Chorionic villus sampling
• D. Maternal serum screening

Answer: (A)

Sampling fetal tissue for genetic confirmation of Down syndrome is best accomplished by chorionic villus sampling, which collects placental tissue (chorionic villi) that carries the fetus’s genetic material. This allows direct karyotyping or chromosomal microarray to diagnose Down syndrome in the first trimester. Amniocentesis samples amniotic fluid containing fetal cells and is diagnostic too, but it is typically performed later in pregnancy and does not involve sampling tissue. Ultrasound provides imaging and may detect structural issues but not a definitive chromosomal diagnosis. Maternal serum screening estimates risk without providing a diagnostic result. Therefore, sampling fetal tissue for direct genetic analysis is achieved with chorionic villus sampling.