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What is Amniocentesis?

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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 29 August 2016
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Amniocentesis is a form of prenatal testing in which the amniotic fluid is analyzed for signs of birth defects or other problems. The procedure is purely elective, although it may be recommended for some mothers who are at higher risk, and it is carried out on an outpatient basis. When a doctor recommends amniocentesis for a patient, he or she should discuss the risks and benefits of the procedure, allowing the patient to come to an informed decision.

Doctors often recommend that women over 35 receive an amniocentesis screening, since there is a risk of Trisomy 21, or Down Syndrome, in babies born to older women. Women who have a family history of genetic defects may undergo amniocentesis, as will women who want to clarify or confirm abnormal test results from other prenatal screenings. Amniocentesis is also sometimes used when women are carrying a baby with a conflicting blood type, to ensure that the fetus is in good health.

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When a woman comes in for an amniocentesis appointment, she will be asked to lie on an exam table and her abdomen will be sterilized with iodine. The doctor will use an ultrasound machine to visualize the abdomen, including the uterus and the amniotic sac. A needle will be carefully guided into the amniotic sac to take a small sample of fluid, ideally without touching the baby, and the fluid will be sent out for testing; a number of tests can be performed on amniotic fluid, taking up to three weeks in some laboratories.

Typically, amniocentesis is performed around the 16th week of pregnancy. Technically, it can be carried out as early as the 11th week, but there is a greater risk of complications or miscarriage earlier on in the pregnancy. Even when carried out in the 16th week, the risk of miscarriage is typically around one in 200, with some clinics having a rate as low as one in 400. After amniocentesis, a women may feel cramped and sore. A doctor should be consulted about any breakthrough bleeding, fluid leakage, or other symptoms of a problem with the baby.

An alternative to amniocentesis is chorionic villus sampling. Chorionic villus sampling can be carried out at an earlier stage of the pregnancy, but it also carries more risks. For women who want reassurance and answers early, it is certainly an option, however.

Generally, a doctor will ask patients to come in to discuss amniocentesis results. A negative result indicates that no abnormalities were found, greatly increasing the chance of a healthy baby. However, it is impossible to test for every single possible birth defect, and miscarriage or other events are still possible; even after negative results, women should take care of their bodies during pregnancy. If the results are positive for a problem, the doctor will discuss what that means with the patient, and options will be discussed as well.

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