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Amniocentesis is the removal of a small amount of amniotic fluid (water that surrounds a developing baby) from the uterus. It is done in a doctor's office or hospital clinic, usually when a woman is about 16 weeks pregnant.
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 then tested for any of the following, depending on your risk factors:
Most tests are done to look for 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 chromosome abnormality is
Down syndrome, which is caused by an extra #21 chromosome.
Some inherited genetic diseases can be tested for prenatally. Examples are:
Test results for inherited genetic diseases are usually ready in 1-5 weeks, depending on the type of test done.
Amniotic fluid can also be tested for neural tube defects. The standard test measures a protein called alpha-fetoprotein (AFP) and detects over 99% of all open neural tube defects. The results are ready in one week or less.
- Obesity
- Previous abdominal surgery
- Previous infection in pelvic organs
Local by injection (optional)
You will lie on an examining table. First, your doctor will do an
ultrasound
scan (sonogram), which shows a picture of the uterus and the fetus. This allows the doctor to choose a safe spot for inserting the amniocentesis 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 A few teaspoons of amniotic fluid are withdrawn.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 again uses ultrasound to ensure that the fetal heartbeat is normal. In most cases, ultrasound imaging will be used throughout the procedure.
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. Some women say that amniocentesis 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.
Amniocentesis is a routine procedure. It is usually safe, but does have some risks. Risks and common safety concerns are listed below:
- 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 amniocentesis usually depends on your special risks, concerns, and family history. Your doctor can help answer any further questions you may have. None. Amniocentesis is done in your doctor's office or at a hospital clinic. - 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. Although more than 95% of women who undergo amniocentesis will have normal results, no prenatal test can guarantee the birth of a healthy baby. There are no tests that can rule out all potential problems. Amniocentesis, however, has an accuracy rate of between 99.4%-100% for diagnosis of chromosome abnormalities. - 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
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. Copyright © EBSCO Publishing. All rights reserved. |
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