Towards the end of the first trimester of pregnancy, around week 12, all pregnant women are instructed to perform the nuchal translucency test (TN), an ultrasound analysis in which the nuchal fold of the fetus will be measured.
But what is it nuchal foldHow is it measured and for what? In the region of the baby's neck, fluid accumulates physiologically and transiently at this stage of pregnancy. This accumulation can be seen by means of an ultrasound from the ninth week of gestation and to obtain reliable results it is measured between week 10 and 14 when the fetus has a caudal skull length, that is, from head to toe, between 38mm and 84 mm
How is the nuchal fold measured?
For measure the nuchal fold The specialist looks for the baby to be placed sideways so that a longitudinal cut can be seen. It then proceeds to measure the maximum thickness of the subcutaneous translucency between the skin and the soft tissue that covers the cervical spine.
The increase in nuchal translucency thickness, that is, when the measurement exceeds the thickness of 3mm, is associated with an increased risk of chromosomal abnormalities. Excessive fluid accumulation can be explained by an overexposure of type VI collagen encoded by a gene on chromosome 21. It is the most sensitive and specific early ultrasound marker suspected of Trismomy 21 or Down Syndrome.
The ultrasound of week 12, in which the nuchal fold of the fetus is measured, is a presumption or suspicion test. The ultrasound analysis performed by a specialist doctor is used to detect indicators that the baby may have Down syndrome. It is not a diagnostic test, but certain ultrasound-detectable images are usually indicative of chromosomal or developmental abnormalities. This also evaluates the presence of nasal bone and a growth of the fetus according to the weeks of pregnancy.
The measurement that has produced the nuchal fold is combined with another prenatal test that is performed in the first trimester of pregnancy: Triple Screening, also known as “triple test” or “first trimester prenatal risk index test” (also the there is the second trimester) that serves to detect possible chromosomal abnormalities related to trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome).
Triple screening and nuchal fold
Triple screening is a non-invasive test performed through a blood sample from the mother that combines three parameters, hence its name. It is a biochemical analysis that is carried out between week 11 and 13 of gestation that measures two substances produced by the placenta and the embryo, a protein and a hormone: the protein A of the blood plasma associated with pregnancy (PAPP-A) and the subunit Free beta of human chorionic gonadotropin (fßhCG). The third parameter is the measurement of the nuchal fold that the ultrasound has thrown.
Screening is performed with the results, that is, the values are compared with other relevant data such as the mother's age, race, weight and the percentage of probability of chromosomal abnormalities is evaluated.
The test is a way of early detection of the possibility that the baby may have any chromosomal abnormality and it helps to avoid unnecessary amniocentesis, however, being a test that does not yield absolute results, it can also become a double-edged sword producing an unjustified anguish in the pregnant woman.
Results of the nuchal fold measurement
The results of triple screening They show the calculation of a risk index based on the Protocol of the Fetal Medicine Foundation, applied in nuchal translucency measurements.
The cut-off point is 1/270, that is to say that when the result is less than 1/270, it means that there is a greater possibility of a chromosomal alteration, on the contrary, when it yields a result greater than 1 / 270, means that there is less chance of it.
When the result is less than 1/270 it is recommended to continue with the study, or performed a chorionic biopsy or an amniocentesis, the only prenatal tests that give a 99% reliable diagnosis of chromosomal abnormalities. However, the decision to perform any of these tests is always a final choice of the couple, since they are invasive tests that are not without risk.
