Which prenatal test obtains tissue from the chorion to detect congenital abnormalities?

• A. Amniocentesis
• B. Chorionic villus sampling
• C. Percutaneous umbilical blood sampling
• D. Ultrasound

Answer: (B)

Chorionic villus sampling uses tissue from the chorion, the outer fetal part of the placenta, to detect congenital abnormalities. Because the chorionic villi contain the same genetic material as the fetus, this sample lets you analyze fetal chromosomes and genes early in pregnancy, typically around the first trimester (about 10 to 13 weeks). The genetic material from the placental tissue is used for karyotyping, microarray, and targeted genetic tests, enabling rapid diagnosis of chromosomal abnormalities or genetic disorders.

In contrast, amniocentesis collects fetal cells from amniotic fluid later in pregnancy, usually after 15 weeks, to assess fetal karyotype or specific conditions but at a later stage. Percutaneous umbilical blood sampling retrieves fetal blood from the umbilical cord for fetal blood testing or transfusion, not tissue from the chorion. Ultrasound is an imaging modality used to assess anatomy and growth, without obtaining tissue for genetic analysis.