Pregnancy: Amniocentesis

Pregnancy: Amniocentesis
Amniocentesis is a test used to detect medical conditions in at-risk babies.

Amniocentesis is the most common prenatal diagnostic test. It is usually performed after 15 weeks of pregnancy, but can also be done later if medically necessary.

What is amniocentesis?

Amniocentesis involves inserting a fine needle into a pregnant woman’s uterus to take a sample of amniotic fluid directly from the amniotic sac. The procedure is a way to collect and analyze fetal cells present in the amniotic fluid to diagnose various conditions that could affect the baby.

When is it recommended to have amniocentesis?

Your doctor may recommend amniocentesis for several reasons.

  • If a prenatal screening test shows a high risk of trisomy 21 or another chromosome abnormality
  • If a genetic condition runs in your or your partner’s family and could be inherited by the fetus
  • If the medical team suspects an amniotic fluid infection, particularly if there’s a delay in the growth of the fetus

How is the amniocentesis test done?

Amniocentesis is performed by an obstetrician-gynaecologist. Guided by ultrasound, the doctor withdraws 20–30 ml of amniotic fluid, which is about 10 percent of the total amount in the uterus. Amniotic fluid replenishes itself regularly, so the procedure has no impact on the fetus.

The appointment lasts about 15 minutes, and most of that time is spent preparing for the test. The procedure itself is very quick. It isn’t painful, but you may feel some discomfort.

Depending on the type of analysis, the results may take anywhere from a few days to a few weeks.

What are the risks of amniocentesis?

The main risk associated with amniocentesis is miscarriage. This occurs in about 1 in 300 cases, though some studies suggest the probability is even lower. Much more rarely, amniocentesis can cause an infection.

It’s normal to experience stomach cramps after having amniocentesis. It’s generally recommended to rest for 24 hours following the procedure. In rare cases, women may notice bleeding or leaking of amniotic fluid from the vagina. Should this happen, or if you develop a fever, it’s a good idea to speak to a doctor.

Choosing whether to end a pregnancy
In some cases, the results of an amniocentesis test can mean having to decide whether to terminate the pregnancy. This is not an easy decision to make.

If you find yourself in this position, don’t hesitate to talk to your loved ones or your health care team. Speaking with parents of children with disabilities or with couples who chose to terminate their pregnancy may also be helpful. Contact your health and social services centre (CSSS) for information about local parent or support groups.
Deciding whether to terminate a pregnancy for medical reasons can be heartbreaking, as the parents face losing not only their baby, but also the dreams they had for them. Don’t hesitate to consult a psychologist or other resources if you need support. It could help you identify what’s at stake and find ways to better cope with your grief.


Things to keep in mind

  • Amniocentesis is a diagnostic procedure used to test for medical conditions in a baby considered to be at risk.
  • The procedure is quick and generally painless.
  • In rare cases, amniocentesis can lead to miscarriage.


Naître et grandir

Scientific review: Jacinthe Santerre, genetic counsellor, CHU Sainte-Justine
Research and copywriting: The Naître et grandir team
Updated: April 2020



Note: Please note: Hyperlinks to other websites are not updated regularly, and some may have changed since publication. If a link is no longer valid, use search engines to find the information you’re looking for.

  • Audibert, François, et al. “Joint SOGC-CCMG Guideline: Update on Prenatal Screening for Fetal Aneuploidy, Fetal Anomalies, and Adverse Pregnancy Outcomes.” Journal of Obstetrics and Gynaecology Canada, vol. 39, no. 9, 2017, pp. 805–817.
  • CHUM. “L’amniocentèse.”
  • Doré, Nicole, and Danielle Le Hénaff. From Tiny Tot to Toddler: A practical guide for parents from pregnancy to age two. Quebec City, Institut national de santé publique du Québec.
  • Le Commissaire à la santé et au bien-être. Consultation sur les enjeux éthiques du dépistage prénatal de la trisomie 21, ou syndrome de Down, au Québec [Consultation on the ethics of prenatal screening for trisomy 21, or Down syndrome, in Quebec]. Consultation report, Quebec City, 2008, 120. pp.
  • Ministère de la Santé et des Services sociaux. “Trisomie 21.”
  • Salomon, L.J., et al. “Risk of miscarriage following amniocentesis or chorionic villus sampling: Systematic review of literature and updated meta-analysis.” Ultrasound in Obstetrics and Gynecology, vol. 54, no. 4, 2019, pp. 442–451.
  • Wilson, R.D., et al. “Amended Canadian Guideline for Prenatal Diagnosis (2005) Change to 2005-Techniques for Prenatal Diagnosis.” SOGC Clinical Practice Guidelines, no. 168, 2005.