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What is Amniocentesis

This is a procedure where a small amount of the fluid surrounding the fetus in the uterus (amniotic fluid) is withdrawn via a needle under ultrasound guidance. It is then sent to the laboratory for testing. This is usually performed around the 15th week of pregnancy.

Reasons for the procedure

In New Zealand, women are offered screening with a combination of an ultrasound scan (nuchal translucency) and a blood test to assess the risk of the fetus having Down Syndrome (Trisomy 21). Women who have had a high risk result with this screening may wish to have an amniocentesis to determine whether the fetus has this genetic abnormality. Some women may not have a high risk of genetic abnormality but wish to have and amniocentesis for reassurance.

Before the procedure

No special preparation is required for an amniocentesis. Sometimes there is some discomfort after the procedure, so it is a good idea to have your partner or a support person to drive you home.

During the procedure

An ultrasound scan is performed to check on the baby’s age and to choose a site for amniocentesis. After scanning, the skin is cleaned with a sterile solution and sterile sheet placed over the abdomen. A very fine needle is then inserted through the abdominal wall into the uterus using ultrasound as a guide. A syringe is attached to the needle and a small amount of amniotic fluid is then withdrawn. The procedure only takes 1-2 minutes. This is mildly uncomfortable, similar to having a blood test.

After the procedure

  • There may be some soreness around the needle site.
  • Please ensure you have someone to drive you home.
  • It is a good idea to have a quiet day after the procedure.
  • If you have any vaginal blood or fluid loss, you should contact your LMC (Lead Maternity Carer) immediately.
  • The results of your amniocentesis will go to your LMC and will take 10-14 days. You can also choose to find out the sex of your baby.

Risks of the procedure

  • There is a risk of miscarriage with amniocentesis of approximately 1 in 1000. Bleeding or cramps after 12 hours are abnormal and you should call your LMC.
  • Very rarely the membranes can rupture and the woman leaks a small amount of clear fluid. This usually reseals and is not a problem.

Limitations of the procedure

This test will not diagnose many abnormalities e.g. cleft lip and palate, spina bifida and cystic fibrosis. Careful scanning will be used to screen for structural abnormalities and an anatomy scan at 18-20 weeks is recommended.

To make an appointment

To book an appointment, please call our nurse on (09) 520 9550 ext 7090, or email her at

Further information, including the testing process, will be given at the time of booking.

To download a general information sheet on amniocentesis, click the link on the left of this page.

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