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The pregnancy outcome is strongly chromosome specific. The most frequently seen trisomic cells in confined placental mosaicism involve chromosomes 2, 3, 7, 8 and 16. The next frequently involved are 9, 13, 15, 18, 20 and 22. [ 8 ]
46,XX/46,XY is either a chimeric or mosaic genetic condition characterized by the presence of some cells that express a 46,XX karyotype and some cells that express a 46,XY karyotype in a single human being. [1] [2] [3] While some individuals with this condition may be classified as intersex, others may have typical male or female characteristics.
In fact, consider that Down syndrome affects about 1:400 pregnancies; if you screened 4000 pregnancies with a Quad test, there would probably be 10 Down syndrome pregnancies of which the Quad test, with its 80% sensitivity, would call 8 of them high-risk. The quad test would also tell 5% (~200) of the 3990 normal women that they are high-risk.
Family history of a chromosomal abnormality or other genetic disorder; Parents are known carriers for a genetic disorder; Advanced maternal age (maternal age above 35). AMA is associated with increase risk of Down's syndrome and at age 35, risk is 1:400. [citation needed] Screening tests are usually carried out first before deciding if CVS ...
PUBS provides a means of rapid chromosome analysis and is useful when information cannot be obtained through amniocentesis, chorionic villus sampling, or ultrasound (or if the results of these tests were inconclusive); this test carries a significant risk of complication and is typically reserved for pregnancies determined to be at high risk ...
An example of an algorithm for determining the indication for prenatal genetic testing for trisomy 21 (Down syndrome), wherein the genetic blood test (in center) is performed by detecting cffDNA in a blood sample from the mother. [60] Trisomy 21. Fetal trisomy of chromosome 21 is the cause of Down's syndrome.
Chorionic villi are projections from the placenta that carry the same genetic makeup as the baby. During this method of prenatal testing, a sample of chorionic villi is removed from the placenta to be tested. This test is performed 10–13 weeks into pregnancy and results are ready 7–14 days after the test was done. [18]
Circulating cffDNA can be detected in maternal blood between the 5th and the 7th week of gestational age, [12] however more fetal DNA is available for analysis usually after 10 weeks, because the amount of fetal DNA increases over time. [13] cffDNA, RNA and intact fetal cells can all be used to assess the genetic status of the fetus non-invasively.