ad. 9. What is nuchal translucency? Increased NT
Nuchal translucency i.e. a fluid accumulated beneath the skin on the fetal neck is a typical characteristic of a baby at the stage of 11+0-13+6 weeks of pregnancy. Increased volume of the fluid (increased nuchal translucency, increased NT) is a symptom, not a disorder. Such a situation occurs in about 9% of all the examinations performed. In this case, the examiner is obliged to clarify the potential reasons of this situation, i.e. first to exclude the genetic syndromes (10% of fetuses with increased NT) and then possible congenital defects.
Very often an increased nuchal translucency is not connected with any anomaly. It is just an indication to exclude most common reasons: aneuploidies with the use of chorionic villus sampling and amniocentesis, and anatomical defects through an early fetal anatomy assessment together with the heart assessment. If the results turn out to be normal, the whole problem can be considered non-important.
The measurement of NT is reliable only if performed in the right time, i.e. 11+0-13+6 weeks of pregnancy and carried out by a specialist with a certificate of the Fetal Medicine Foundation (FMF). The list of the specialists can be found on the following website: wwww.fetalmedicine.com. Please take note that since 2008 the FMF has not required taking a practical exam, and the requirements have been lowered significantly in order to bring this method into general use. At present, a specialist can obtain the certificate after sending only three images showing NT measurement and taking part in an online course on the Foundation’s website.
In our opinion, the measurement of nuchal translucency is one of the most difficult measurements performed during the whole pregnancy, requiring a comprehensive training and good reproducibility. The difficulty consists in seizing a fetus in a particular position, proper adjusting of the machine and, in many cases, patience of a specialist and a patient. The measurement of NT has no strict norms or so-called absolute values, nevertheless, it influences the final result of an examination, i.e. the value of the computer calculated risk of chromosomal aberrations. The result in the form of a description with the calculations, but without an image showing the method of carrying out the NT measurement is incomplete (a clear documentation of the measurement is essential). In our opinion, in this area, the specialist’s experience in the first trimester examinations and detecting genetic syndromes is of the greatest importance, e. g. the Down syndrome occurs on average in 1 in 1000 pregnancies. In order to detect only 20 such cases, statistically speaking, the number of 20,000 screening tests would have to be performed, or the specialist would have to examine patients with already suspected anomalies by another specialist and analyze the further outcome of these pregnancies.