What is the association of nuchal translucency greater than 3 mm?

Nuchal translucency (NT) measurements play an important role in prenatal screening, particularly in assessing the risk of chromosomal abnormalities in the fetus. An NT measurement greater than 3 mm indicates a higher risk of aneuploidies, specifically Trisomy 21 (Down syndrome), as well as other chromosomal abnormalities such as Trisomy 18 and 13.

Several studies have demonstrated that an increased NT measurement is associated with a significant increase in the likelihood of these aneuploidies. The threshold of 3 mm is a commonly used cutoff during the first trimester screening, whereby a measurement exceeding this value prompts further diagnostic testing and counseling, leading to a more informed decision-making process for expectant parents.

This elevated risk does not imply that every baby with increased NT will have an anomaly, but it certainly warrants closer evaluation through additional testing, such as chorionic villus sampling (CVS) or amniocentesis, for definitive diagnosis and appropriate management. Thus, the association between a nuchal translucency greater than 3 mm and aneuploidies, notably Trisomy 21, is well recognized in obstetric practice.