The nuchal fold It is a region of the neck of the fetus where fluid accumulates in a physiological or natural way. This accumulation of fluid can be seen by ultrasound and is used to detect early suspicion of Down syndrome or Trisomy 21. Measurement of the baby's nuchal fold in pregnancy is performed between weeks 10 and 14 of gestation, using a marker ultrasound is called nuchal translucency. This test is performed on all pregnant women.
The nuchal translucency test (TN) allows to obtain reliable results around the 12th week of pregnancy when the fetus has a column length between the neck and the sacrum, between 38 mm and 84 mm. The specialist measures the maximum thickness of the subcutaneous translucency between the skin and the soft tissue that lines the cervical spine. Increased thickness of the nuchal translucency is associated with Down syndrome. In numbers, it is considered that if the thickness of the nuchal fold exceeds 3 mm, there is a risk of chromosomal abnormalities. It is the most sensitive and specific early ultrasound marker for suspected Trisomy 21 or Down syndrome.
The excessive accumulation of fluid is due to overexposure of type VI collagen encoded by a gene on chromosome 21. The cut-off point is 1/270. When the result is less than 1/270, there are greater possibilities of chromosomal alterations, on the contrary, when the result is greater than 1/270, it means that there are less possibilities that they exist.
Nuchal translucency, which is performed on the 12 week ultrasound, is a test of presumption or suspicion. It does not make a diagnosis, it is only an indicator of chromosomal or developmental abnormalities. In this same ultrasound, the growth of the nasal bone is also evaluated according to the weeks of pregnancy, a marker that also establishes the suspicion of Down syndrome.
The results of the ultrasound at week 12 are compared with those obtained by another test of the first trimester of pregnancy: the Triple Screening, which is used to detect possible chromosomal abnormalities related to trisomy 21 (Down syndrome) and trisomy 18 (syndrome of Edwards) using a blood sample from the mother that combines three parameters. These results are in turn compared with the values of other relevant data such as the mother's age, race, and weight, and the percentage of probability that there are chromosomal abnormalities is evaluated, but none of them is capable of giving a reliable diagnosis. .
Chorionic biopsy (tissue sample) or amniocentesis (removal of a small amount of amniotic fluid from the maternal uterus) are the only prenatal tests that are 99 percent reliable in diagnosing chromosomal abnormalities, including Down's Syndrome.
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