[Weeks 16-20] Is an amniocentesis necessary after week 16?
In short, no. Amniocentesis is not recommended for every pregnant woman. If a prenatal screening test shows a high-risk result or there is another reason to suspect a chromosomal abnormality, you and your healthcare provider can discuss whether amniocentesis is appropriate for you. Amniocentesis is an invasive prenatal diagnostic test in which a needle is used to collect a small amount of amniotic fluid. The risk of procedure-related complications is low, but it is not zero, so it is important to discuss the potential benefits and risks with your healthcare provider before deciding. Cells and other material from the baby in the amniotic fluid can be analyzed to diagnose chromosomal conditions such as Down syndrome, Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). The time needed for results depends on the type of analysis. A rapid test such as FISH can provide information about common chromosomal abnormalities relatively quickly, while karyotype analysis involves culturing cells and examines the number and larger structural changes of the chromosomes. FISH is useful for rapidly checking specific chromosomal abnormalities, but it does not detect all chromosome abnormalities. When necessary, its findings are interpreted together with a full karyotype or other diagnostic tests. The tests performed and turnaround times can vary between laboratories and medical centers.