Isolated Increased Nuchal Translucency with Normal Karyotype: A Narrative Literature Review

Introduction: Nuchal translucency (NT) measurement during first-trimester ultrasound is an important marker for chromosomal abnormalities and fetal malformations. However, a significant proportion of fetuses with increased NT have a normal karyotype, raising challenges for prognosis and management. Objective: This narrative review summarizes the current literature on isolated increased NT with normal karyotype, focusing on causes, prognosis, and prenatal management strategies. Methods: A literature search was conducted in PubMed, Scopus, and ScienceDirect databases for articles published from 2010 to 2024 using keywords such as "nuchal translucency," "normal karyotype," and "prenatal diagnosis." Studies addressing isolated increased NT cases with normal chromosomal results were included. Results: Isolated increased NT may be linked to congenital heart defects, genetic syndromes undetected by standard karyotyping, infections, or structural anomalies, or remain idiopathic. Prognosis correlates with NT thickness and includes risks of miscarriage, fetal anomalies, and neurodevelopmental delay. Advanced genetic testing (chromosomal microarray, exome sequencing) increases diagnostic yield. Prenatal monitoring with detailed ultrasound and genetic counseling are essential. Conclusion: Isolated increased NT with normal karyotype is associated with a variable risk of adverse outcomes, requiring careful prenatal assessment and follow-up.