The needle is inserted through the abdomen and the uterus into the amniotic fluid that surrounds the fetus. A small amount of the fluid is withdrawn -- approximately one ounce (30cc). This amniotic fluid contains cells from the fetus that can be tested. These cells have the same genetic makeup as the fetus.
http://www.parents.com/pregnancy/stages/amniocentesis/should-i-have-an-amniocentesis/
You might consider genetic amniocentesis if: 1  You had positive results from a prenatal screening test. 2  If the results of a screening test — such as the first trimester screen or prenatal cell-free DNA screening — are positive or worrisome, you might opt for amniocentesis to confirm or rule out a diagnosis.
http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/why-its-done/prc-20014529
The vast majority of amniocentesis procedures are uneventful and the results indicate a normal fetus. Thoughtful consideration of possible abnormal findings and the issues and choices that would have to be made place amniocentesis in a unique position.
http://www.parents.com/pregnancy/stages/amniocentesis/should-i-have-an-amniocentesis/
1 Fetal lung maturity testing involves taking a sample of amniotic fluid and testing it to determine whether the baby's lungs are mature enough for birth. 2  Diagnosis of fetal infection. 3  Occasionally, amniocentesis is used to evaluate a baby for infection or other illness.
http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/why-its-done/prc-20014529
1 Amniocentesis can also be used to determine the maturity of the lungs of the fetus or the cause of unknown fever in the mother. 2  For genetic testing, chromosome analysis, and the evaluation of an abnormal alpha feto-protein test, amniocentesis is usually performed between the 16th and 21st weeks of pregnancy.
http://www.medicinenet.com/amniocentesis/article.htm
Amniocentesis is a procedure whereby a sample of fluid is removed from the amniotic sac for analysis. The amniotic sac is in the uterine cavity. The amniotic sac is the fluid-filled structure inside a pregnant woman's uterus within which the baby lives. Fetal cells, proteins, and fetal urine freely move within this sac.
http://www.medicinenet.com/amniocentesis/article.htm
Because amniocentesis is usually done at 16 to 18 weeks, and the results take two to three weeks, abnormal results need to be discussed and choices and options reviewed. She might need to consult with others such as pediatric or surgical specialist or genetic counselor.
http://www.parents.com/pregnancy/stages/amniocentesis/should-i-have-an-amniocentesis/
1 Genetic testing. 2  Genetic amniocentesis involves taking a sample of amniotic fluid and testing it for certain conditions, such as Down syndrome. 3  Fetal lung testing. 4  Fetal lung maturity testing involves taking a sample of amniotic fluid and testing it to determine whether the baby's lungs are mature enough for birth.
http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/why-its-done/prc-20014529
Genetic amniocentesis can provide information about your baby's genetic makeup. Generally, genetic amniocentesis is offered when the test results might have a significant impact on the management of the pregnancy or your desire to continue the pregnancy. Genetic amniocentesis is usually done between week 15 and 20 of pregnancy.
http://www.mayoclinic.org/tests-procedures/amniocentesis/basics/why-its-done/prc-20014529
Answer. Amniocentesis is a procedure done during the early part of the second trimester of pregnancy (usually between 16 and 18 weeks). The pregnant woman lies down with her abdomen exposed. Ultrasound (sonogram) is used to show the doctor where the baby and placenta are located and where to safely insert the needle.
http://www.parents.com/pregnancy/stages/amniocentesis/should-i-have-an-amniocentesis/
when to do amniocentesis
Do amniocentesis between the 16th and 21st weeks of pregnancy. Amniocentesis is usually done between the 16th and 21st weeks of pregnancy.