Amniocentesis can be used to determine the maturity of the lungs of the fetus or the cause of unknown fever in the mother. For genetic testing, chromosome analysis, and the evaluation of an abnormal alpha feto protein test, amniocentesis is usually performed between the 15th and 18th weeks of pregnancy.
Amniocentesis is a procedure whereby fluid is extracted from the amniotic sac.
The amniotic sac is the fluid-filled structure inside the pregnant uterus within which the baby lives. Fetal cells, proteins, and fetal urine freely move within this sac. During amniocentesis, fluid is removed by placing a long needle through the abdominal wall into this sac. Sometimes, the woman's skin is injected first with a local anesthetic, but this is not always necessary. Occasionally, the amniocentesis needle is guided into the sac with the help of ultrasound imaging.