Nuchal dating scan which came first ramones or sexpistols
This leaves the measurement of nuchal transparency as a potentially useful first trimester screening tool.
Abnormal findings allow for early careful evaluation of chromosomes and possible structural defects on a targeted basis.
Between 65 and 85% of trisomic fetuses will have a large nuchal thickness.
Further, other, non-trisomic abnormalities may also demonstrate an enlarged nuchal transparency.
Until recently, the only reliable ways to determine if the fetus has a chromosomal abnormality was to have an invasive test such as amniocentesis or chorionic villus sampling, but such tests carry a risk of causing a miscarriage estimated variously as ranging between 1% Most women, especially those with a low risk of having a child with Down syndrome, may wish to avoid the risk to the fetus and the discomfort of invasive testing.In pregnancies affected by Down syndrome there is a tendency for the levels of human chorionic gonadotropin (h CG) to be increased and pregnancy-associated plasma protein A (PAPP-A) to be decreased.The advantage of nuchal scanning over the previous use of just biochemical blood profiling is mainly the reduction in false positive rates.At 12 weeks of gestational age, an "average" nuchal thickness of 2.18mm has been observed; however, up to 13% of chromosomally normal fetuses present with a nuchal translucency of greater than 2.5mm.Thus for even greater accuracy of predicting risks, the outcome of the nuchal scan may be combined with the results of simultaneous maternal blood tests.
This method identifies about 75% of affected fetuses while screening about 5% of pregnancies.