Step 1: Amniocentesis is a medical procedure used to test for chromosomal abnormalities and genetic defects in a fetus by analyzing amniotic fluid. Step 2: While determining diseases (Option a) is a major medical advantage, the procedure also reveals the chromosomal sex of the fetus. Step 3: The misuse of this information for female foeticide is considered a significant social disadvantage and has led to a statutory ban on sex determination in many countries.