(692) What’s the Significance of Nuchal Translucencies <3mm but >95th Percentile in the Era of NIPT?

An increased nuchal translucency (NT) is a well-known marker for genetic and structural anomalies. Increased NT is typically defined either as a measurement > 3mm or by values > 95th percentile. However, there is limited data on the significance of NT > 95th percentile but < 3mm. We hypothesize that using the 95th percentile as a threshold for evaluation may enhance detection of anomalies in pregnancies with normal non-invasive prenatal testing (NIPT).

Study Design:

This retrospective study included patients who received prenatal ultrasounds at a large, academic center between 2018 and 2023. Participants with an NT< 3mm, normal NIPT and a completed early or comprehensive anatomy ultrasound were included. Patients were divided into two groups- increased (>95th percentile) vs normal (< 95th percentile) NT. Other data collected included invasive genetic testing, fetal echocardiography, and perinatal outcomes. Analysis was performed via Student’s t-test, Mann Whitney’s U test, Chi square or Fisher’s Exact test.

Results:

A total of 176 cases were included: 58 (33.0%) had an increased NT and 118 (67.0%) had a normal NT. Results are in Table 1. Although odds of detecting anomalies were 78% higher with an increased NT, this was not significant (OR 1.78, 95% CI 0.54–5.84). No association was seen between an increased NT and anomaly detection on either early (p=0.82) or full anatomy (p=0.53). Patients with increased NT were more likely to get invasive genetic testing (p=0.0004) and fetal echocardiograms (p=< 0.0001). Increased testing did not improve detection of genetic (p=1.00) or cardiac (p=1.00) anomalies. Of note, patients with increased NT were more likely to be Asian/Pacific Islander or White (p< 0.0001) and have a male fetus (p=0.011).

Conclusion:

In patients with normal NIPT, an increased NT >95th percentile but < 3mm was not linked to a higher rate of anomaly detection. Patients were more likely to pursue additional testing despite similar outcomes. Thus, an increased NT >95th percentile but < 3mm may have limited clinical utility and could contribute to unnecessary testing and patient anxiety.