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What is an amniocentesis?


An amniocentesis is a prenatal test that allows your healthcare practitioner to gather information about your baby's health from a sample of your amniotic fluid that surrounds your baby in the uterus. The most common reason to have an amniocentesis is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome. Amniocentesis is usually done when a woman is between 16 and 22 weeks pregnant.


What are the risks of amniocentesis?


Some of the risks of an amniocentesis include, but are not limited to, pain, bleeding, vaginal bleeding, leaking of amniotic fluid, rupture of membranes, infection, cramping, and contractions. Sometimes more than one attempt may be required to obtain an adequate sample. Sometimes, the procedure ma fail to identify all genetic problems. Rarely will the patient have to return for a repeat amniocentesis because there was not an adequate sample obtained.


The risk that most patients are worried about is the risk for miscarriage.  Approximately 1 in 200 to 1 in 300 attempts at amniocentesis may result in a miscarriage or loss of the pregnancy.


What is the procedure like?


Before you have your amniocentesis, an ultrasound is done to measure your baby and check his basic anatomy. For the amnio itself, you lie on an examining table and your belly is cleaned with alcohol or an iodine solution. The entire procedure is performed in a sterile, clean manner. Ultrasound is used to pinpoint a pocket of amniotic fluid a safe distance from both the baby and the placenta. You may choose to have your abdomen numbed first with a local anesthetic, but the pain from the anesthesia injection is likely to be worse than that of the amniocentesis itself, and most moms-to-be decide that one needle is enough. Then, under continuous ultrasound guidance, the doctor inserts a long, thin, hollow needle through your abdominal wall, through the womb wall, and into the sac of fluid around your baby. A small amount of amniotic fluid is removed through the needle. Withdrawing the fluid can take a few minutes but usually takes less than 30 seconds. Your baby will make more fluid to replace what's taken out


You may feel some cramping, pinching, or pressure during the procedure — or you may feel no discomfort at all. The amount of discomfort or pain varies among women and even from one pregnancy to the next. Then, the baby is checked after the procedure to make sure that the baby is doing well.


What can I do after the procedure?


After the procedure, you'll need to take it easy for the rest of the day, so arrange for someone to drive you home. You may have some minor cramping for a day or so. Most people are able to go to work and resume normal activities the day after the amniocentesis. Avoid any heavy lifting, intercourse, and air travel for the next two to three days. If you have significant cramping or vaginal spotting, or you're leaking amniotic fluid, call your practitioner immediately. It could be a sign of impending miscarriage. Also call right away if you have a fever, which could be a sign of an infection.


What information do I obtain from having an amniocentesis?


Amniocentesis can be performed for:

  •                                 FISH

FISH stands for Fluorescence In Situ Hybridisation. This is a special test which can be performed on fetal cells obtained by amniocentesis.  The result is usually available in 3-4 days. The test does not detect all chromosomal abnormalities; this FISH test specifically looks at chromosomes 21, 18, 13, X and Y.

  •                                 Fetal Karyotype

 This is a test that can be performed on fetal cells obtained by amniocentesis. The fetal karyotype is determined by analyzing the total number of chromosomes and sex chromosomes, and also the structure of the specific chromosomes to make sure that there is no missing or additional material, no structural abnormalities, and a variety of other possible chromosome abnormalities.

  •                                 Fetal Chromosomal Microarray Analysis.

This is a test that can be performed on fetal cells obtained by amniocentesis. CMA is a relatively new test that is designed to look at the chromosomes in a more detailed way. CMA provides expanded genetic testing for a large number of serious genetic disorders not detected by routine chromosome analysis.



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