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Glossary: Amniocentesis

Friday, March 16, 2012 - 14:04

Contributing Author: Guy Slowik FRCS

Here are definitions of medical terms related to amniocentesis:

Alpha-fetoprotein: A protein, also called AFP, which the fetus produces in its liver and brain. The level of alpha-fetoprotein tends to increase in the amniotic fluid when a fetus has an open neural tube defect or abdominal wall defect. The protein can be found in adults as well; it's particularly abundant in the blood of adults with certain forms of liver cancer.

Amniocentesis: A prenatal test in which amniotic fluid is taken out of the uterus.

Amniotic fluid: The fluid that surrounds the fetus.

Anencephaly: A congenital defect in the development of the brain. Bones in the skull and parts of the brain may be missing or poorly developed. An infant with anencephaly will either be stillborn or will die shortly after birth.

Cervix: The lower part of the uterus, often referred to as the neck of the uterus.

Chorionic villus sampling (CVS): A prenatal test to detect chromosomal abnormalities in which cells from the placenta are analyzed. CVS can be done at 10 to 12 weeks of pregnancy.

Chromosomes: The units along which genes are arranged. Humans have two sets of 23 chromosomes, with one set coming from each parent.

Down syndrome: A common genetic disorder in which there is an extra copy of chromosome number 21 (trisomy 21), resulting in mental retardation and physical malformations.

Edward's syndrome: A genetic disorder in which there is an extra copy of chromosome number 18, resulting in severe mental retardation.

Genetic counseling: A counseling process for those with either a family history of a genetic disorder or those who are at risk for having a child with a genetic disease.

Karyotype: The array of chromosomes in a cell.

Multiple marker screening (MMS): A prenatal blood test that tests for substances in the blood that are linked to genetic abnormalities. The MMS can be a triple screen, which tests for three substances, or a quadruple screen, which tests for four substances.

Neural tube defect: A common birth defect in which the neural tube, which gives rise to the central nervous system, develops abnormally, causing death or serious disability. Spina bifida and anencephaly are examples of neural tube defects.

Patau's syndrome: A genetic disorder in which there is an extra copy of chromosome number 13, resulting in severe mental retardation.

Pre-eclampsia: Also called toxemia; an illness that occurs during the second half of pregnancy characterized by high blood pressure, swelling of the hands, feet and face, and large amounts of protein in the urine.

Premature labor: Labor occurring before 37 full weeks of pregnancy.

Rh factor: A protein D found on the surface of red blood cells. Those lacking the protein are Rh negative, while those who have it (the majority of the population) are Rh positive.

Sickle cell anemia: An inherited blood disease in which the red blood cells contain an abnormal from of hemoglobin, the protein that transports oxygen from the lungs to the rest of the body.

Spina bifida: A failure during embryonic development of the vertebral column to fuse completely.

Tay-Sachs disease: A hereditary disorder in which a deficiency of the enzyme hexosaminidase causes progressive mental retardation, paralysis, dementia and blindness, which usually results in death by age 5. Tay-Sachs is most common in families of Eastern European descent.

Turner syndrome: A genetic disorder affecting only females where there is only one X chromosome or one of the two X chromosomes is damaged.