Introduction
Nuchal translucency (NT) is a subcutaneous fluid collection behind fetal neck and it is physiologically present in the first trimester in all fetuses1. In the early ’90, Nicolaides introduced NT measurement as part of first trimester screening for trisomies 21, 13 and 182 and over the years an increased NT has been associated with several pathological conditions such as adverse pregnancy outcome3-4, chromosomal abnormalities other than common trisomies, genetic syndromes5-9, and structural anomalies3;8, in particular cardiac malformations10-11. Therefore, pregnancies with an increased NT are considered at high risk and detailed fetal ultrasound, fetal echocardiography, genetic counselling and chorionic villous sampling (CVS)/amniocentesis are usually offered to these patients.
Reference ranges and percentiles for NT based on gestational age have been established in a large study by Snijders et al.12. International guidelines, however, do not show complete agreement regarding the cut off of NT value or percentile that requires further investigations; the most commonly used are either 3.5 mm, 3 mm or the 99th percentile13-17(Table 1). Usually, cases of NT between the 95th-99th percentile are managed as healthy pregnancies.
Recently, the accuracy of ultrasonographic technology has markedly increased and new genetic tests such as CGH-array (Comparative Genomic Hybridization) and exome sequencing, have been introduced in clinical practice, allowing to be more accurate in the diagnosis of fetal anomalies, chromosomal abnormalities and genetic syndromes.
The aim of our multicentric study was to evaluate all women with NT between 95th and 99th percentile and discuss a possible new cut off for fetal and genetic tools usually provided to higher cut offs.