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Amniocentesis

An amniocentesis is a diagnostic test which provides definitive genetic information about your baby. For example, if you have a condition which places you at an increased risk for having a child with a genetic disorder (such as Down Syndrome), an amniocentesis will provide a definitive yes or no answer as to whether the baby is affected.

During an amniocentesis, a small amount of amniotic fluid is removed from the sac surrounding the baby and tested. The sample of fluid (less than one ounce) is removed through a very thin needle inserted into the uterus through the abdomen, and the fluid is replaced naturally within 24 hours. The procedure is performed using ultrasound guidance so that the exact position of the needle may be followed throughout the procedure. The fluid is then sent to a laboratory for analysis.

Different tests can be performed on a sample of amniotic fluid, depending on the genetic risk and indication for the test. Any patient may undergo amniocentesis if she so desires. The procedure is ideally performed between 16-18 weeks’ gestation (though it may be performed any time after 15 weeks’ gestation and as late as the third trimester in certain circumstances). The risk of miscarriage following an amniocentesis varies in different studies. It is generally cited to be around 1 in 300 procedures, though in our experience, the risk of pregnancy loss is approximately 1 in 1000 procedures or less. Most patients tell us that the procedure is less uncomfortable than they anticipated, and the level of discomfort is comparable to what you might expect when having your blood drawn.





The most common conditions for which a patient may be offered an amniocentesis would include the following:
  1. The patient has a fetal abnormality diagnosed at the time of an ultrasound
  2. The patient is going to be 35 years old or older at the time of delivery
  3. The patient has family history of certain birth defects or genetic disorders (such as cystic fibrosis).
  4. The patient has previously had a child with a birth defect.
  5. The patient has a “positive” 1st or 2nd trimester screen through the California State Prenatal Screening program
  6. The patient has a desire, for one reason or another, to know for certain the genetic composition of the baby (even if the screening tests are otherwise normal)
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