Amniocentesis is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections,in which a small amount of amniotic fluid, which contains fetal tissues, is sampled from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for genetic abnormalities. It is the sampling of amniotic fluid using a hollow needle inserted into the uterus, to screen for developmental abnormalities in a fetus.
Before the start of the procedure, a local anesthetic can be given to the mother in order to relieve the pain felt during the insertion of the needle used to withdraw the fluid. After the local is in effect, a needle is usually inserted through the mother's abdominal wall, then through the wall of the uterus, and finally into the amniotic sac. With the aid of ultrasound-guidance, a physician punctures the sac in an area away from the fetus and extracts approximately 20 ml of amniotic fluid.
If used for prenatal genetic diagnosis, fetal cells are separated from the extracted sample. The cells are grown in a culture medium, then fixed and stained. Under a microscope the chromosomes are examined for abnormalities.
