What Is Amniocentesis? - Definition, Purpose, Procedure & Risks

Instructor: Marisela Duque

Marisela teaches nursing courses at the college level. She also works as a unit educator, teaching experienced nurses about changes in nursing practice.

Upon completion of this lesson, you will be able to define amniocentesis and describe how it is performed, its purpose, and potential risks involved. A short quiz follows the lesson.


Pregnancy should be an exciting and joyful time for the mother-to-be. The last few months are usually filled with anticipation of the birth and a lot of rapid growth for the baby. When the delivery day finally arrives, most mothers are happy to finally meet their little one, and not be pregnant anymore. In some rare instances, complications occur, and the baby may have one or several birth defects. Luckily, modern medicine has advanced so that a variety of diagnostic tests are available to ensure that the baby is healthy, and to help parents of babies that will be born with complications be better prepared. One such diagnostic test is an amniocentesis.

What Is Amniocentesis?

Amniocentesis is a diagnostic procedure performed on pregnant women that looks for genetic and chromosomal abnormalities (birth defects) in the fetus. Some common conditions that may be detected include Down syndrome (trisomy 21), cystic fibrosis, and neural tube defects (spina bifida). This test is generally performed between weeks 14 and 20 of pregnancy, but may be performed in the third trimester to look for certain conditions, such as infection and fetal lung maturity. It is highly accurate (98-99%) and is usually recommended by obstetricians if the fetus is at a higher risk for any of the health problems mentioned above. Doctors determine that risk by taking into account some laboratory findings, such as the triple test, family history, and maternal age.

How Is This Procedure Done?

The whole procedure takes about 45 minutes. First, you must have a full bladder before beginning, which can be difficult considering that it sometimes feels like the baby is already dancing on your bladder. Despite the discomfort, this step is important in order to better visualize the baby during the procedure. Then, you are asked to lie on your back while an ultrasound is done so that the doctor can see the baby on a screen. Oftentimes, a numbing cream or injection is placed on the belly where the procedure will occur. The doctor will also wash your belly with an antimicrobial liquid to prevent any infections.

Finally, a long, thin needle is inserted into the belly and into the uterus (womb) where a sample of amniotic fluid is collected (about three to four teaspoons). While this sounds scary, this part is actually really fast. The amniotic fluid is the liquid that surrounds the baby in the womb; it contains cells from the fetus. This fluid sample is sent for testing, and the results take about two weeks to return. Most women discover that their fetus is normal. The mother usually waits another 20-30 minutes after the procedure before going home, to ensure both mom and baby are okay.

What Are the Risks and Side Effects to Mother and Baby?

The mother may experience some side effects after the procedure is completed. Common side effects include cramping, mild pain, and slight bruising around the injection site. These side effects are usually mild and only last for a short time.

Although amniocentesis is considered a safe procedure, there are some associated risks involved. These include:

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