Towards the end of the first trimester of pregnancy, around week 12, shown to all pregnant women performing the test measurements of nuchal (TN), an analysis of ultrasound that measured the fetal nuchal fold.
But, what is nuchal fold, do you measure and for what? Fluid accumulates in the region from the neck of the baby of physiological and transient form at this stage of gestation. This accumulation can be seen through an ultrasound from the ninth week of gestation and to obtain reliable results is measured between 14 and 10 weeks when the fetus has a length of caudal skull, i.e. head to bum, between 38 mm and 84 mm.
How to measure the nuchal fold?
For measuring the nuchal fold the specialist looks for baby to stand sideways so you can see a longitudinal cut. It then proceeds to measure the maximum thickness of the subcutaneous translucency between skin and soft tissue overlying the cervical spine.
Measurements nuchal thickness increased, or when the measurement exceeds 3mm thickness, is associated with an increased risk of chromosomal abnormalities. Excessive fluid accumulation can be explained by an overexposure of collagen type VI encoded by a gene on chromosome 21. It is the scoreboard early ultrasound more sensitive and specific of suspected Trismomia 21 or Down’s syndrome.
Of the 12 week ultrasound, which measures the fetal nuchal fold, is a test of presumption or suspect. The analysis carried out ultrasound by a medical specialist serves to detect indicators that the baby may have Down syndrome. It is not a diagnostic test, but that certain detectable by ultrasound images tend to be indicators of chromosomal abnormalities or developmental. Thus also evaluates the presence of nasal bone and growth of the fetus according to the weeks of pregnancy.
The measurement that has thrown the nuchal fold merges with other prenatal testing that is performed in the first trimester of pregnancy: the Triple Screening, also known as “triple test” or “proof of the first trimester prenatal risk index” (it there is also the second quarter) which serves for detecting possible chromosomal abnormalities associated with trisomy 21 (Down syndrome) and Trisomy 18 (Edwards syndrome).
The Triple screening and nuchal fold
The Triple screening is a non-invasive through a blood sample from the mother that combines three parameters, hence its name. It is a biochemical analysis that is performed between the week 11 and 13 of gestation that measured two substances produced by the placenta and embryo, a protein and a hormone: A protein in the blood plasma associated with the pregnancy (PAPP-A) and the beta subunit free chorionic gonadotropin human (Fβhcg). The third parameter is the measurement of crease nuchal which has thrown the ultrasound.
With the results is carried out a screening, i.e. Comparing the values with other relevant data such as the age of mother, race, weight and evaluates the percentage of probability that there are chromosomal abnormalities.
The test is a way of detected at an early stage the possibility that the baby may have some chromosomal alteration and helps prevent unnecessary amniocentesis, however, it is a test that cannot support absolute results, can also become a double-edged weapon causing undue distress in pregnant women.
The measurement of the nuchal plieque
The results of the Triple screening toss the calculation of an index of risk based on the Protocol of the Fetal Medicine Foundation, applied in measurements of nuchal measurements.
The cut-off point is situated in 1/270, is that when the result which is less than 1/270, it means that there are greater possibilities that exist a chromosomal alteration, on the other hand, when dropping a result greater than 1/270, means there is less chance that there is.
When the result is less than 1/270 it is recommended to proceed with the study, either chorionic biopsy or an amniocentesis, unique prenatal tests that throw a 99% reliable chromosomal diagnosis. Without however, the decision to make one of these tests always is a final couple’s choice, since they are invasive which are not exempt of risks testing.