Amniocentesis is a simple office procedure involving the removal of a small amount of amniotic fluid (the fluid which surrounds the baby). It is performed most often at about 16-17 weeks (a "genetic amnio") to evaluate the fetal chromosomes (e.g. to determine the presence of Down Syndrome). We also learn the fetal sex from the amnio and we learn the level of alpha-fetoprotein (afp) level in the amniotic fluid.
Genetic amniocentesis is usually offered to patients who will be 35 years old or older at the time of delivery. It may also be suggested to patients who have had a previous baby with birth defects or have been exposed to situations
associated that can cause possible chromosome damage.
Also amniocentesis is recommended if the expanded alpha-fetoprotein blood test has an abnormal result.
The primary risk of amniocentesis is miscarriage. This may occur in about 1/250 to 1/500 procedures
(2-4 per 1000). The risk of injuring the fetus with the amniocentesis needle is very low.
Making the Decision
The decision for an amniocentesis is a very personal one. Some patients under the age of 35 might want to have an amniocentesis. They feel that they would rather accept a small risk of miscarriage rather than take the chance of missing a detectable severe abnormality. In general, amniocentesis is suggested if you will be at least 35 years old at the time of delivery, or if you have other indications and risk factors as noted above and only if termination of an abnormal pregnancy would be considered. Formal genetic counseling is available for a detailed evaluation of your situation.
Generally, results are available about 10 days after the amniocentesis is performed. We call all patients with their results as soon as they are available. Please let us know in advance whether or not you would like to know the sex of the baby.
*A new test called FISH (fluorescence in-situ hybridization) can provide a preliminary amniocentesis result in 3 days. Ask us about this.
*Non-Invasive Prenatal Testing can detect many of the same conditions as amniocentesis, but not ALL of them.