What is the difference between NIPT and amniocentesis?

They answer different questions, and this is the single most important distinction in prenatal testing. NIPT is a screening test. It analyses placental DNA in your blood and estimates whether the chance of certain conditions is increased or decreased. It carries no risk to the pregnancy. It cannot give you a definite answer. Amniocentesis is a diagnostic test. A needle is used to take a small sample of amniotic fluid containing cells from the baby, and those chromosomes are examined directly. It gives a definitive answer. It carries a small procedure-related risk of miscarriage. Because NIPT looks at placental DNA rather than the baby directly, it can occasionally be misleading — the placenta and baby can have different chromosomes, a situation called confined placental mosaicism. Amniocentesis also detects far more. NIPT typically covers three trisomies; amniocentesis examines all chromosomes and can be extended with microarray to detect small deletions and duplications. There is one more difference that matters for future pregnancies: NIPT cannot tell whether Down syndrome is caused by an extra chromosome, a translocation, or mosaicism. Those have different recurrence risks for future pregnancies, and only a diagnostic test can distinguish them. ACMG's position is that when NIPT is high-risk, confirmatory testing by CVS or amniocentesis is recommended.