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Home > Wellness > Health Library > Amniocentesis
Amniocentesis is a test to look at the fluid that surrounds your baby (fetus) in the uterus. Amniotic fluid has cells and other substances that can give clues about the health of your fetus.
For this test, a needle is put gently through your belly into your uterus. About 2 Tbsp (30 mL) of fluid is taken out and looked at.
This test may be done between weeks 15 and 20 to look at the baby's genes. It can also be used later in pregnancy to see how the baby is doing.
Amniocentesis is often done around week 16 to see if a fetus has certain types of birth defects. It can also tell the sex of a fetus.
Amniotic fluid has cells that have been shed by your growing fetus. The cells are checked for the number and size of chromosomes. This can show if there are any problems that put the baby at risk for certain conditions, such as Down syndrome. But this test can't find many common birth defects. These include cleft lip, cleft palate, heart problems, and some types of intellectual disability.
Testing is most often done as soon as possible so women and their families have time to think about their options.
Amniocentesis may be done in the third trimester if your doctor thinks you may have an infection of the amniotic fluid (chorioamnionitis). Or your doctor may do amniocentesis in late pregnancy to check your baby for certain types of infections or other rare problems.
In some cases, this test may be used to find out how much your baby's lungs have developed.
Amniocentesis may also be done late in pregnancy to remove some amniotic fluid if too much has built up in the amniotic sac (polyhydramnios).
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Amniocentesis may be done during your second trimester to find certain birth defects.
You may choose to have this test because:
Amniocentesis can tell the sex of your baby. This is important when you or the father may pass on a disease that occurs mainly in one sex (sex-linked). Examples include hemophilia and Duchenne muscular dystrophy. These both occur mainly in males.
Amniocentesis may be done in the third trimester if your doctor thinks you may have an infection of the amniotic fluid (chorioamnionitis). Or your doctor may do amniocentesis to check your baby for certain types of infections or other rare problems.
You may be asked to empty your bladder just before the test.
You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done.
Talk to your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form( What is a PDF document? ).
Amniocentesis is done by your obstetrician in the doctor's office or in the hospital. You probably won't need to stay overnight in the hospital unless problems occur during the test.
You will lie on your back on an exam table. Your lower belly will be cleaned with a special soap.
Your doctor will use a fetal ultrasound to check the position of your fetus and the placenta. Ultrasound uses sound waves to make a picture of the uterus, your fetus, and the placenta on a TV screen. Your fetus's heart rate can also be watched during the test using ultrasound. For more information, see the topic Fetal Ultrasound.
With the ultrasound picture as a guide, your doctor will gently put a thin needle through your belly and into your uterus. This will not hurt your fetus or the placenta. If your fetus moves too close to the needle, the doctor will take the needle out and try again in another spot.
The doctor will take about 2 Tbsp (30 mL) of amniotic fluid. Then the needle is removed. The site is covered with a bandage.
The whole test takes about 15 minutes. The thin needle is only in your belly for 1 to 2 minutes. Your fetus's heart rate and your blood pressure, pulse, and breathing will be checked before, during, and after the test.
You will feel a sharp sting or burn in your belly where the needle is put in. This lasts for only a few seconds. When the needle is put into your uterus, you will feel a sharp cramp for a few seconds.
When the amniotic fluid is taken out, you may get a feeling of pulling or pressure in your belly. To keep yourself comfortable, breathe slowly and relax your belly muscles during the test.
Amniocentesis is mostly very safe. There is a small chance (about 1 out of 900) that this test may cause a miscarriage.footnote 1
There is also a risk of too much bleeding (hemorrhage), infection of the amniotic fluid, or leakage of the fluid. In very rare cases, a fetus may be poked by the needle during the test. Your doctor does all he or she can to put the needle in a safe spot. Most fetuses move away from the needle tip.
Amniocentesis has a very small risk of causing bleeding that could mix your blood and your fetus's blood. So if you have Rh-negative blood, you will be given the Rh immunoglobulin vaccine (such as RhoGAM). This can prevent Rh sensitization, which could harm your fetus if he or she has Rh-positive blood.
After the test, you may have some mild cramping. Do not do any strenuous activity for several hours after the test. Also, do not douche, use tampons, or have sex after the test. By the next day, you can do your normal activities, unless your doctor tells you not to.
Call your doctor right away if:
Amniocentesis is a test to look at the amniotic fluid that surrounds your baby (fetus) in the uterus.
Normal amniotic fluid is clear to light yellow in color and does not contain any harmful bacteria. The cells can be tested for problems.
Normal results from amniocentesis do not guarantee that your baby will be healthy.
You may not be able to have the test, or the results may not be helpful, if:
Akolekar R, et al. (2015). Procedure-related risk of miscarriage following amniocentesis and chorionic villus sampling: a systematic review and meta-analysis. Ultrasound in Obstetrics and Gynecology, 45(1): 16–26. DOI: 10.1002/uog.14636. Accessed April 5, 2017.
Current as ofSeptember 5, 2018
Author: Healthwise StaffMedical Review: Sarah A. Marshall, MD - Family MedicineE. Gregory Thompson, MD - Internal MedicineAdam Husney, MD - Family MedicineKathleen Romito, MD - Family MedicineKirtly Jones, MD - Obstetrics and Gynecology, Reproductive Endocrinology
Current as of:
September 5, 2018
Medical Review:Sarah A. Marshall, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology, Reproductive Endocrinology
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