In the context of a first trimester screen, what is considered an abnormal nuchal translucency (NT) measurement?

An abnormal nuchal translucency (NT) measurement during a first trimester screen is defined as greater than 3 mm. NT is a sonographic measurement taken during an ultrasound, usually between 11 and 14 weeks of gestation, and reflects the amount of fluid accumulation in the nuchal space at the back of the fetal neck.

An NT measurement greater than 3 mm is significant because studies have shown that it is associated with an increased risk of chromosomal abnormalities, such as Down syndrome (trisomy 21), as well as other congenital anomalies and adverse pregnancy outcomes. The measurement serves as a useful screening tool, prompting further assessment and counseling to manage potential risks effectively.

Measurements less than 2 mm are generally considered normal and associated with a lower risk of aneuploidies. While an NT measurement between 2 mm and 3 mm is often viewed as borderline, it does not carry the same heightened risk associated with measurements greater than 3 mm. Thus, understanding the implications of the NT measurement helps clinicians provide better care and counseling for expectant parents.