What is an Amnioscentesis?

An amniocentesis, often called an amnio is a tool of diagnosis that doctors use to identify chromosomal, structural and genetic abnormalities in fetuses. A newer use of the amniocentesis is paternity testing — amniotic fluid carries the DNA of the fetus, and correctly identifies parentage 99% of the time. Approximately 200,000 amnios are performed every year, and although they do carry a slight risk of miscarriage and infection, are considered a safe procedure.

Amniotic fluid, which is contained within the protective sac around the baby, contains cells that have been sloughed off by the fetus. In these cells are genetic markers that can help a doctor determine if the baby has chromosomal defects such as Downs syndrome or Trisomy 21, structural defects such as anencephaly (incomplete/missing brain) or spina bifida (open spine), and genetic conditions such as cystic fibrosis. Amnios are done typically between 14 to 20 weeks gestation, but may be done as early in the pregnancy as 11 weeks. Amniocentesis that is performed later in pregnancy may used to determine if the baby's lungs are mature enough for premature delivery. It may also be used later in pregnancy to determine Rh compatibility, which requires treatment.

Preparation for an amniocentesis is simple — you just need to have a full bladder. The procedure typically takes about 45 minutes. Your skin on the abdomen will be prepped and cleaned, and you may receive a local or topical anesthetic. A hollow needle is inserted into the uterus through the abdomen using an ultrasound as a guide, and your doctor will be extremely careful not to harm the baby with the needle. How far along you are will determine how much amniotic fluid will be withdrawn, however, a rule of thumb is 1cc/per week gestation. You may feel a sharp, tingling pain for a short while, typically a few seconds.

Although it is considered a safe procedure, amniocentesis is not without risk. Infection at the site of insertion, as well as internally, may be a risk. Miscarriage is the most serious complication, only occurring about 1% of the time. You may experience some slight cramping after the procedure, so take it easy for at least a day afterwards. Results of your amnio may take up to a couple of weeks, so you'll have to be patient. With "normal" results, there will not be any chromosomal abnormalities, and the levels of alpha fetoprotein will be within normal ranges.

The amniocentesis is an optional, elective test that you and your spouse should discuss carefully with your doctor. If you have no risk factors associated with the conditions the amniocentesis screens for, then you may choose not to have the test. Some people get the test in order to prepare themselves for a disabled child, to get advanced treatment for their child or to consider if they will be able to carry the baby to term. For others who firmly believe that they would carry a baby to term regardless of disability, they may find that the amnio is not for them. If the procedure seems needlessly risky for you, ask your doctor for other alternatives.

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