Amniocentesis is ideally performed at which gestational window?

• A. 11-14 weeks gestation
• B. 15-22 weeks gestation
• C. 23-26 weeks gestation
• D. 27-30 weeks gestation

Answer: (B)

Amniocentesis is timed in the mid-second trimester because this is when there is enough amniotic fluid and fetal cells to obtain a reliable diagnostic sample, while the procedure carries a lower risk of miscarriage compared with earlier pregnancy and still allows time for culture and testing. The commonly accepted window is about 15 to 22 weeks gestation (often around 15–18 weeks for karyotyping).

Earlier in pregnancy (11–14 weeks) is the window for chorionic villus sampling, not amniocentesis. Later in pregnancy (23–26 weeks or 27–30 weeks) increases procedural risks and offers less benefit for standard genetic testing, making it less ideal.