Which prenatal test is performed earlier in pregnancy to detect fetal abnormalities by sampling placental tissue?

• A. Amniocentesis
• B. Chorionic villus sampling
• C. PUBS
• D. Ultrasound

Answer: (B)

The key idea is obtaining fetal genetic information as early as possible by sampling tissue that reflects the fetus’s genome. Chorionic villus sampling does this by collecting placental tissue that contains fetal cells, typically in the first trimester around 10 to 13 weeks. Analyzing these cells allows chromosomal and certain genetic tests to be done earlier than other methods. Amniocentesis, by contrast, samples amniotic fluid and is usually performed later in pregnancy (about 15 to 20 weeks). Ultrasound provides imaging to assess anatomy but does not sample tissue. PUBS involves sampling fetal blood from the umbilical cord and is used later when specific fetal conditions arise. So, sampling placental tissue for early genetic testing is best accomplished with chorionic villus sampling.