amniocentesis

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amniocentesis

(ăm'nēō'sĕntē`sĭs), diagnostic procedure in which a sample of the amniotic fluid surrounding a fetus is removed from the uterus by means of a fine needle inserted through the abdomen of the pregnant woman (see pregnancypregnancy,
period of time between fertilization of the ovum (conception) and birth, during which mammals carry their developing young in the uterus (see embryo). The average duration of pregnancy in humans is about 280 days, equal to 9 calendar months.
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). The procedure can be done in a hospital or in a doctor's office. Ultrasoundultrasound
or sonography,
in medicine, technique that uses sound waves to study and treat hard-to-reach body areas. In scanning with ultrasound, high-frequency sound waves are transmitted to the area of interest and the returning echoes recorded (for more detail, see
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 is used to determine the location of the fetus during the procedure. Fetal cells in the fluid can be grown in the laboratory and studied to detect the presence of certain genetic disorders (e.g., Down syndromeDown syndrome,
congenital disorder characterized by mild to severe mental retardation, slow physical development, and characteristic physical features. Down syndrome affects about 1 in every 730 live births and occurs in all populations equally.
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, Tay-Sachs diseaseTay-Sachs disease
, rare hereditary disease caused by a genetic mutation that leaves the body unable to produce an enzyme necessary for fat metabolism in nerve cells, producing central nervous system degeneration.
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) or physical abnormalities (e.g., anencephaly, or incomplete development of the brain). The sample also can be examined to determine the gender of the fetus and has been used to preselect the sex of the baby, a practice that, although controversial, is much used in some parts of the world. Amniocentesis cannot be used to detect such defects as congenital heart disease or cleft palatecleft palate,
incomplete fusion of bones of the palate. The cleft may be confined to the soft palate at the back of the mouth; it may include the hard palate, or roof of the mouth; or it may extend through the gum and lip, producing a gap in the teeth and a cleft lip, which is
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.

Amniocentesis is generally recommended when there is a family history of genetic disorders or when the woman is over age 35 and therefore at a higher risk of having a baby with a chromosomal abnormality. The procedure is usually carried out around the 14th or 15th week of pregnancy, when there is sufficient amniotic fluid and abortionabortion,
expulsion of the products of conception before the embryo or fetus is viable. Any interruption of human pregnancy prior to the 28th week is known as abortion. The term spontaneous abortion, or miscarriage, is used to signify delivery of a nonviable embryo or fetus due
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 is still an option. It can also be used in the third trimester (after 30 weeks) when Rh incompatibility (see erythroblastosis fetaliserythroblastosis fetalis
, hemolytic disease of a newborn infant caused by blood group incompatibility between mother and child. Although the Rh factor is responsible for the most severe cases of erythroblastosis fetalis, the disease may be produced by any of the other blood
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) is suspected, or to determine the status of the fetus in early or late delivery or when there are signs of fetal distress.

See also birth defectsbirth defects,
abnormalities in physical or mental structure or function that are present at birth. They range from minor to seriously deforming or life-threatening. A major defect of some type occurs in approximately 3% of all births.
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; chorionic villus samplingchorionic villus sampling
(CVS) or chorionic villus biopsy
(CVB) , diagnostic procedure in which a sample of chorionic villi from the developing placenta is removed from the uterus of a pregnant woman (see pregnancy) using a fine needle inserted through the abdomen or
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; embryo screeningembryo screening,
procedure (see genetic testing) in which a single cell is removed from an embryo two or three days after it has been conceived through in vitro fertilization and tested for genetic abnormalities.
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.

amniocentesis

[¦am·nē·ō‚sen′tē·səs]
(medicine)
A procedure during pregnancy by which the abdominal wall and fetal membranes are punctured with a cannula to withdraw amniotic fluid.