American Board of Obstetrics & Gynecology (ABOG) Qualifying Practice Exam 2026 - Free Obstetrics & Gynecology Practice Questions and Study Guide

The nuchal translucency (NT) measurement is most accurate for diagnosing aneuploidy during the gestational age of 11 to 13 weeks, particularly when performed between 11 weeks and 13 weeks and 6 days. At this stage, the NT measurement is a well-established screening tool for conditions such as Down syndrome (trisomy 21) and other chromosomal abnormalities.

The reason around the 13-week mark is optimal is due to the physiological changes occurring in early pregnancy. Between 11 and 13 weeks, the nuchal fold is still present and more measurable, allowing for better accuracy. After this period, the NT measurement begins to decrease as the nuchal space becomes less defined and the overall risk assessment for aneuploidy changes.

In summary, the accuracy of nuchal translucency measurements for detecting aneuploidy peaks around 11 to 13 weeks, making a measurement taken at approximately 13 weeks highly reliable for screening purposes.