Which procedure involves removal and analysis of a small sample of fetal cells from amniotic fluid, typically performed at 14-18 weeks?

• A. Chorionic Villus Sampling
• B. Amniocentesis
• C. Cordocentesis
• D. Percutaneous Umbilical Blood Sampling (PUBS)

Answer: (B)

Amniocentesis involves removing a small amount of amniotic fluid with a needle inserted through the mother's abdomen under ultrasound guidance, and then analyzing the fetal cells in that fluid. This is typically done around 14 to 18 weeks of gestation to perform chromosomal analysis and prenatal genetic testing, since the fetal cells can be cultured to detect numerical or structural chromosomal abnormalities. The procedure may also allow assessment of components like amniotic fluid alpha-fetoprotein for neural tube defect screening in appropriate contexts.

Chorionic villus sampling, in contrast, collects placental tissue and is usually performed earlier in pregnancy to obtain similar genetic information but from a different source. Cordocentesis (PUBS) retrieves fetal blood from the umbilical cord for rapid karyotyping or testing of blood conditions, not from amniotic fluid.