Amniocentesis

Amniocentesis (also referred to as amniotic fluid test or AFT), is a medical procedure used in prenatal diagnosis of genetic abnormalities and fetal infections cite web|url=http://www.health.harvard.edu/diagnostic-tests/amniosentesis.htm|title=Diagnostic Tests - Amniocentesis|publisher=Harvard Medical School|accessdate=2008-07-15] , in which a small amount of amniotic fluid, which contains fetal tissues, is extracted from the amnion or amniotic sac surrounding a developing fetus, and the fetal DNA is examined for genetic abnormalities.

Procedure

Before the actual procedure, a local anesthetic is sometimes given to relieve the pain when inserting the needle used to withdraw the fluid. A needle is usually inserted through the mother's abdominal wall or at the end of the vagina, and through the wall of the uterus into the amniotic sac. With assistance from ultrasound, a physician aims towards an area of the sac that is away from the fetus and extracts a small amount of amniotic fluid for testing. The puncture heals, and the amniotic sac replenishes the liquid over a day or so. After the amniotic fluid is extracted, the fetal cells are separated from it using a centrifuge, and the fetal chromosomes are examined for abnormalities. Various genetic testing may be performed, but the three most common abnormalities tested for are Down syndrome, Trisomy 18 and spina bifida. Amniocentesis can be performed as soon as sufficient amniotic fluid surrounds the fetus to allow a sample to be recovered relatively safely, usually no earlier than the 14th week of pregnancy. Often, genetic counseling is offered in conjunction with amniocentesis.

Risks

Although the procedure is routine, possible complications include infection of the amniotic sac from the needle, and failure of the puncture to heal properly, which can result in leakage or infection. Serious complications can result in miscarriage. Other possible complications include preterm labor and delivery, respiratory distress, postural deformities, fetal trauma and alloimmunisation (rhesus disease). The risk of amniocentesis-related miscarriage is generally thought to be 1 in 200, [http://www.webmd.com/content/article/129/117333.htm Amniocentesis Risk Overrated? ] ] although a recent study has indicated this may actually be much lower, perhaps 1 in 1,600. In contrast, the risk of miscarriage for chorionic villus sampling (CVS) is believed to be approximately 1 in 100, although CVS may be done up to four weeks earlier, and may be preferable if the possibility of genetic defects is thought to be higher [ [http://content.nejm.org/cgi/content/abstract/320/10/609 NEJM - The safety and efficacy of chorionic villus sampling for early prenatal diagnosis of cytogenetic abnormalities ] ] .

New knowledge has also been discovered in blood sampling.Blood can be extracted from the mother, and then tested

ee also

* Chorionic villus sampling
* Percutaneous umbilical cord blood sampling
* Prenatal diagnosis

References