What is amniocentesis?

Amniocentesis is a diagnostic procedure in which a small amount of amniotic fluid — the fluid surrounding your baby — is withdrawn using a fine needle, guided continuously by ultrasound for safety and precision. The fluid contains fetal cells, which are analysed for chromosomal conditions (karyotype or chromosomal microarray) or specific genetic mutations.

Why is amniocentesis done?

  • To give a definitive diagnosis when a screening test (NT scan, combined screening, or NIPT) suggests a higher risk
  • When parents want complete certainty rather than a risk estimate
  • To investigate a structural finding seen on the anomaly scan

Unlike NIPT, which is a screening test, amniocentesis provides a direct, definitive answer.

When is it done?

Amniocentesis is typically performed between 15 and 20 weeks of pregnancy.

How to prepare

Little specific preparation is needed. Dr. Chandak will advise if a full or partially full bladder helps with the scan on the day. Tell her about any blood-thinning medicines or known bleeding disorders beforehand.

What happens during the procedure

Using continuous ultrasound guidance to keep the needle path safely away from the baby, a fine needle is passed through the abdomen into the amniotic sac, and a small amount of fluid is withdrawn. The procedure itself usually takes 10 to 20 minutes.

What happens after

Rest is recommended for the rest of the day, avoiding heavy activity. Mild cramping or light spotting is common and usually settles on its own. Results typically take one to two weeks for a full karyotype; a rapid preliminary result (FISH) for the most common conditions can often be available within a few days.

Is amniocentesis safe?

Possible risks Amniocentesis carries a small procedural risk of miscarriage, generally cited at around 0.5%. Performing the procedure under continuous ultrasound guidance, as is done here, helps keep this risk as low as possible. Dr. Chandak will discuss your individual risk in full before you decide.

Frequently asked questions

Amniocentesis is highly accurate — generally over 99% — for detecting chromosomal conditions, since it directly analyses the baby's own cells rather than estimating risk.

The commonly cited risk is around 0.5%, though your individual risk can vary. Dr. Chandak will discuss this specifically in relation to your pregnancy.

A rapid preliminary result for the most common chromosomal conditions is often available within a few days; the complete karyotype analysis typically takes one to two weeks.

Most women feel a brief pinch and pressure similar to a blood test, rather than significant pain. Local anesthesia can be used if needed.