Also found in: Medical.
embryo screening,procedure (see genetic testinggenetic testing,
medical screening for genetic disorders, by examining either a person's DNA directly or a person's biochemistry or chromosomes for indirect evidence. Testing may be done to identify a genetic disorder a person has, whether the disorder is already evident or not,
..... Click the link for more information. ) in which a single cell is removed from an embryo two or three days after it has been conceived through in vitro fertilizationin vitro fertilization
(IVF), technique for conception of a human embryo outside the mother's body. Several ova, or eggs, are removed from the mother's body and placed in special laboratory culture dishes (Petri dishes); sperm from the father are then added, or in many cases a
..... Click the link for more information. and tested for genetic abnormalities. At this stage the embryo consists of about eight genetically identical cells. The embryo itself is unaffected and continues to grow while the selected cell's genes are replicated and tested for genetic defects. Embryo screening, also known as embryo biopsy, preimplantation genetic diagnosis, and preimplantation genetic screening, permits genetic testing to occur before an embryo is implanted into the womb. Such procedures are used when an inheritable disease or a genetic predisposition to a disease is carried by or exhibited in one or both parents. The techniques have also been used to improve the success of in vitro fertilization in general by determining if an embryo has any abnormalities that might lead to a miscarriage after the embryo is implanted.
Embryo screening has been used successfully to screen for such diseases as cystic fibrosiscystic fibrosis
, inherited disorder of the exocrine glands (see gland), affecting children and young people; median survival is 25 years in females and 30 years in males.
..... Click the link for more information. and Tay-SachsTay-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.
..... Click the link for more information. as well as for genes that predispose a person to breast or colon cancer. The procedure can also be used to determine the gender of the embryo. Given this ability, X-chromosome-linked diseases that manifest only in males (hemophiliahemophilia
, genetic disease in which the clotting ability of the blood is impaired and excessive bleeding results. The disease is transmitted through females but almost invariably affects male offspring only.
..... Click the link for more information. , for example) can be "screened" by implanting only female embryos (which will carry but will not develop the disease). Another variation that involves examining the sample to make sure it has the correct number of chromosomes is used for women over 35 (women past that age being statistically more likely to give birth to babies with 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.
..... Click the link for more information. and other chromosomal defects). Embryo screening has also been used to select a child who is a compatible donor for a sibling with a life-threatening disease such as certain anemias and leukemias.
See also amniocentesisamniocentesis
, 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 pregnancy).
..... Click the link for more information. ; 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.
..... Click the link for more information. ; 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
..... Click the link for more information. .