At what week is amniocentesis performed?

Amniocentesis is generally performed after 15 completed weeks, with the exact timing chosen for the clinical question. Many appointments fall in the middle part of pregnancy, although testing can take place later if a new ultrasound finding or another concern arises. Pregnancy dating, the reason for testing and the laboratory work requested all shape the schedule.

Waiting allows more amniotic fluid to surround the baby and avoids the additional concerns associated with early amniocentesis. During the procedure, ultrasound guides a fine needle into a suitable pocket of fluid. The sample contains fetal cells that can be analysed for the specific chromosome or genetic condition discussed during counselling.

Confirm how your due date was established and whether the clinic requires a particular completed week. Ask why the test is being proposed, what information it can add beyond screening or ultrasound, and how long the requested analysis may take. If earlier diagnostic testing is relevant, the clinician can explain whether chorionic villus sampling was or remains an appropriate option for your circumstances.

Following amniocentesis, call your maternity service urgently for clear vaginal fluid, vaginal bleeding, fever, shivering, contractions, or severe or worsening abdominal pain. Follow the same advice whether testing occurred at the usual time or later in pregnancy. If the clinic is closed, use the out-of-hours contact route given at your appointment.

Find out which completed week the clinician recommends for you, what has determined that date and whether waiting would change the usefulness of the result. Ask how amniocentesis compares with NIPT or chorionic villus sampling for your particular question, remembering that a screening test and a diagnostic test provide different kinds of information.