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Screening for Down syndrome by a combination of maternal age and thickness of nuchal translucency in the fetus at 11–14 weeks of gestation was introduced in the 1990s. [7] This method identifies about 75% of affected fetuses while screening about 5% of pregnancies. Natural fetal loss after positive diagnosis at 12 weeks is about 30%. [6]
Perhaps the most common such test uses a measurement of the nuchal translucency thickness ("NT-test", or "Nuchal Scan"). Although 91% of fetuses affected by Down syndrome exhibit this defect, 5% of fetuses flagged by the test do not have Down syndrome. Ultrasound may also detect fetal organ anomaly.
Ultrasound imaging provides the opportunity to conduct a nuchal translucency (NT) scan screening for chromosomal abnormalities such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). Using the information from the NT scan the mother can be offered an invasive diagnostic test for fetal chromosomal ...
Benacerraf pioneered the field of "genetic sonography" [3] with her discovery that nuchal fold thickness–the distance between the occipital bone and the surface of the overlying skin at back of the neck–was a reliable metric for second-trimester diagnosis of Down syndrome.
Maternal serum ADAM 12 and PAPP-A levels at 8 to 9 weeks gestation in combination with maternal age yielded a 91% detection rate for Down syndrome at a 5% false-positive rate. When nuchal translucency data from approximately 12 weeks gestation was added, this increased the detection rate to 97%. [9]
Increased nuchal translucency or other abnormal ultrasound findings; 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.
Down syndrome or Down's syndrome, [12] ... Uses ultrasound to measure nuchal translucency in addition to blood tests for free or total beta-hCG and PAPP-A: Quad screen:
The most common abnormality the test can screen is trisomy 21 (Down syndrome).In addition to Down syndrome, the triple and quadruple screens assess risk for fetal trisomy 18 also known as Edwards syndrome, open neural tube defects, and may also detect an increased risk of Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith–Lemli–Opitz syndrome, and steroid sulfatase ...