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Pronounced: am-KNEE-o-sen-TEE-sis

En Español (Spanish Version)


The removal of a small amount of amniotic fluid (water that surrounds a developing baby) from the uterus


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© 2008 Nucleus Medical Art, Inc.

Parts of the Body Involved

  • Uterus
  • Amniotic sac

Reasons for Procedure

Amniocentesis is most often performed for the following reasons:

  • Mother is over 35 years old (at the time of delivery)
  • Family history of chromosome abnormality
  • Family history of inherited disorder
  • Family history of neural tube defect (problems in spine and brain growth such as spina bifida or anencephaly)
  • To determine whether the baby's lungs are mature
  • Abnormal results from earlier blood screening test such as maternal serum alpha-fetoprotein (AFP)

Cells from the amniotic fluid are grown in the laboratory for 1-2 weeks. They are tested for any of the following, depending on your risk factors:

Chromosome Abnormalities

The standard laboratory testing detects over 99% of all chromosome abnormalities. The results are usually ready within 14 days.

Missing or extra chromosomes lead to serious physical birth defects, mental retardation, or both. The most common is Down syndrome, caused by an extra #21 chromosome.

Inherited Genetic Diseases

Examples are:

Test results for inherited genetic diseases are usually ready in 1-5 weeks.

Neural Tube Defects

The standard test measures a protein called alpha-fetoprotein (AFP). It detects over 99% of all open neural tube defects. The results are ready in one week or less.

Risk Factors for Complications During the Procedure

  • Obesity
  • Previous abdominal surgery
  • Previous infection in pelvic organs

What to Expect


Local (optional)

Description of the Procedure

It is done in a doctor's office or hospital clinic. It is usually when a woman is about 16 weeks pregnant.

Your doctor will do an ultrasound scan (sonogram) to choose a safe spot for inserting the needle. Your abdomen is cleaned, and a very thin needle is inserted through your abdomen into your uterus. A few teaspoons of amniotic fluid are withdrawn.

After the needle is removed, the doctor will make sure that the fetal heartbeat is normal. In most cases, ultrasound imaging will be used throughout the procedure.

How Long Will It Take?

Locating the fetus and inserting the needle can take up to 20 minutes. Withdrawing the fluid takes five minutes. You will be asked to remain on the table for an additional 15 or 20 minutes to relax.

Will It Hurt?

Some women say the procedure doesn’t hurt at all. Others feel cramping when the needle enters the uterus or pressure during the few minutes while the fluid is being withdrawn.

Possible Complications

This is a routine procedure. It is usually safe, but does have some risks:

  • Miscarriage—Average risk for miscarriage is less than 1 in 200. Early amniocentesis (before 15 weeks) may have a somewhat higher risk at less than 1 in 100.
  • Bleeding, cramping, and leaking fluid from the vagina—Occurs in about 1% of women having amniocentesis. Does not usually result in a miscarriage. If you have these symptoms, call your doctor.
  • Infection—Very rare. Great care is taken to prevent this.
  • Harm to the fetus—The risk that the needle will touch the fetus is extremely low.
  • Rh problems—If you have Rh-negative blood type, and the baby's father has Rh-positive blood, you should have an injection of Rh immune globulin after the procedure. This helps prevent Rh disease in the baby.
  • Repeat testing—Very rare. The doctor may not obtain enough amniotic fluid, or the laboratory test cannot be done for some reason. Neither of these means that something is necessarily wrong with the pregnancy, but the amniocentesis will have to be repeated.

Deciding whether or not to have the test usually depends on your special risks, concerns, and family history.

Average Hospital Stay


Postoperative Care

  • Rest for 24 hours after the procedure
  • For the first few hours, avoid physical stress such as lifting and prolonged standing
  • Bathe and shower as usual
  • No heavy exercise or sexual relations for 24 hours


Your results will be available within 10-14 days. About 95% of women who undergo amniocentesis will have normal results. No prenatal test can guarantee the birth of a healthy baby. Amniocentesis has an accuracy rate of between 99.4%-100% for diagnosis of chromosome abnormalities.

Call Your Doctor If Any of the Following Occurs

  • Signs of infection, including fever and chills
  • Nausea or vomiting
  • Pain or cramping in the lower abdomen or shoulder
  • Vaginal bleeding or a loss of fluid from the vagina
  • Redness, swelling, increasing pain, excessive bleeding, or discharge from the amniocentesis site
  • New, unexplained symptoms


American College of Obstetrics and Gynecologists

March of Dimes Birth Defects Foundation


The Canadian Women's Health Network

The Society of Obstetricians and Gynaecologists of Canada


Amniocentesis. March of Dimes website. Available at: Accessed June 5, 2008.

Later Childbearing. American College of Obstetrics and Gynecology website. Available at: Accessed June 5, 2008.

Last reviewed January 2008 by Jeff Andrews, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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