Amniocentesis is a prenatal test used to detect genetic disorders in the fetus. The procedure involves drawing a small amount of amniotic fluid from the uterus, guided by ultrasound, and is performed between weeks 16-23 of the pregnancy.

Two main techniques are used to analyze the genetic material: karyotype (done under a microscope) and CMA (Chromosomal Microarray Analysis) - a newer method that offers a more accurate analysis. 
Though CMA is more expensive than the karyotype analysis, Shaare Zedek offers this test without extra charge to every woman undergoing amniocentesis. Genetic counseling is also provided prior to the procedure, likewise without extra charge. The geneticist provides explanations about the procedure and the various findings that could be detected. If there are unusual findings, a second counseling session might be scheduled.

Amniocentesis can accurately detect a wide range of common genetic diseases, the most common being Down syndrome, which is caused by an excess copy of the 21st chromosome. 
Amniocentesis can also help detect rarer defects in specific genes when one of the parents is a carrier of a genetic disease or if there is any other reason to suspect that the fetus may have a defected gene. Many diseases can be detected in this manner, such as CF, Tay-Sachs, Familial Dysautonomia and more.

Today there are many non-invasive tests available to evaluate the chances of genetic disease, among them nuchal translucency, alpha-fetoprotein, combined tests and more. However, amniocentesis still remains the only way to definitively confirm or rule out a fetal chromosomal problem. 
The recommendation for amniocentesis is done on an individual basis according to the woman's personal medical history as well as her wishes and position on termination of pregnancy in the event that the fetus is diagnosed with a genetic defect.

As with any invasive procedure, amniocentesis has risks, including  miscarriage. Other rare complications include traumatic injury to the fetus and infection. However, on the whole, the risk is minimal. Comprehensive information about the risks and benefits of the test will be provided before the procedure so that the parents can make an informed decision.