The clinical impact of the first-trimester nuchal translucency between the 95th-99th percentiles

Objectives: To evaluate the clinical significance of nuchal translucency (NT) between the 95th-99th percentile in terms of typical and atypical chromosomal abnormalities (ACAs), associated fetal congenital defects and postnatal outcome. Methods: A retrospective cohort study of fetuses with NT between the 95th-99th percentile. Data regarding the rate of associated fetal defects, genetic abnormalities and postnatal outcome were collected. Results: A total of 306 cases of fetuses with an NT between the 95th-99th percentiles were included. The overall rate of genetic abnormalities was 12.1% (37/306). Chromosomal abnormalities were found in 10.1% (31/306) of cases and 2% were ACA (6/306). Within this group, two were pathogenic Copy Number Variants (CNVs) and four were single gene disorders. The overall rate of fetal congenital defects was 13.7% (42/306). All ACAs were found in fetuses with congenital defects. Postnatally, a new diagnosis of a single gene disorder was made in 0.85% of cases (2/236). Conclusions: The presence of an NT between the 95th-99th percentiles carries a 10-fold increased risk of fetal defects, representing an indication for referral for a detailed fetal anatomy evaluation. The risk of ACA is mainly related to the presence of fetal defects, irrespective of the combined test risk.