What is the nuchal translucency scan and when is it done?

"Nuchal translucency is an important ultrasound marker that helps indicate the presence and risk of any chromosomal / genetic abnormalities or structural malformation," explains Dr. Mauro. 

The main chromosomal abnormalities are: chromosome abnormality 21 (Down syndrome), 18 (Edwards syndrome) and 13 (Patau syndrome). The last 2 are extremely serious conditions and incompatible with life. 

Specifically, nuchal translucency is an anatomical space located in the cervical region of the fetus, the thickness and structural features of which are assessed by abdominal ultrasound. Its values are entered into software that evaluates other characteristics of the fetus, the patient, and the pregnancy.

Combined Test

"In addition to nuchal translucency, nasal bone and cardiac flowmetries are examined, along with all fetal anatomy assessable in the first trimester of pregnancy. These data are supplemented with the result of a maternal blood draw called Bitest, which consists of the assay of the free fraction of pregnancy hormone (FreeBeta HCG) and PAPP-A (pregnancy-associated placental protein), in order to increase the sensitivity of the test, which, we recall, is not diagnostic, but probabilistic. 

Taken together, it is referred to as the Combined Test and, in addition, makes it possible to estimate the risk of developing hypertensive disorders peculiar to pregnancy in more advanced stages and to set up a prevention and surveillance program toward this fearsome problem".

The Combined Test aims to reassess the patient's age-related baseline risk. It takes into consideration several variables, both fetal and maternal. Among them, the mother's age is one of the risk elements for the development of chromosomal abnormalities: the greater the age, the greater the risk.

Ultrasound for combined or fetal DNA testing is performed between about 11 and 13 weeks. Its duration depends on: 

• positions of the fetus and its movements;
• physical characteristics of the patient and the tissues.

It can range from 10 to 15 minutes to about half an hour.

The result of the nuchal translucency examination does not have a fixed value, but depends on: 

• gestational age at which it is performed;
• fetal size, which should not exceed 84 mm, a value beyond which the translucency parameter loses reliability. 

"In cases when the Combined Test results highlight an increased risk, counseling will be done about the advisability of acquiring fetal karyotype (numerical and macrostructural assessment of chromosomes) with invasive procedures such as villocentesis or amniocentesis, while in intermediate (moderate) risk cases, the possibility of fetal DNA testing will be discussed with the patient.

Even for fetal DNA testing or NIPT, before we get to the blood draw, a very thorough ultrasound scan must be conducted, which includes the study of fetal anatomy (feasible at about 12 weeks) and measurement of nuchal translucency, which remains the most reliable ultrasound marker for identifying the risk of chromosomal abnormalities or malformations," the doctor continues.

Today, national, European, and international guidelines provide for the study of the fetus to ultrasound-assess organs and systems that were not considered until a few years ago. 

The experience and high resolution of the latest generation of ultrasound scanners make it possible to suspect or diagnose, in some cases, malformative pathologies or high-risk situations so as to set up a course of ultrasound and clinical counseling and/or surveillance to be implemented in a multidisciplinary manner with other specialists, such as the geneticist.

"Ospedale San Raffaele is active in in-depth diagnostics with invasive examinations for situations of increased risk arising from, among other things, abnormal nuchal translucency values. 

A study is being conducted by the Fetal Health Center at Ospedale San Raffaele that evaluates whether or not invasive procedures, which have a modest but real risk of complications, are appropriate in the presence of nuchal translucency values that are at or slightly above the upper limits in the presence of an overall low risk at the Combined Test," Dr. Mauro concludes.