A recent study from Ontario, Canada, unveiled a strong link between the measurements of fetal nuchal translucency and the risk of chromosomal anomalies, including conditions less frequently screened for in current prenatal practices. The findings were published in the recent edition of Journal of American Medical Association.
The study involved a massive group of over 414,000 singleton pregnancies, that illuminated the significance of nuchal translucency measurements as an early indicator of genetic conditions by prompting a reevaluation of existing cutoff points for follow-up testing. Nuchal translucency (NT) measurement with ultrasonography is a common in prenatal screening that primarily targets trisomies 21 (Down syndrome) and 18. Traditionally, a cutoff of 3.5 mm or more was utilized to flag pregnancies for further investigation, like the cell-free DNA (cfDNA) screening or more detailed cytogenetic analysis. However, the findings of this study suggest that risks related with chromosomal anomalies may be significantly elevated even at NT measurements below the conventional 3.5 mm threshold.

This study utilized data from the Better Outcomes Registry & Network, Ontario's perinatal registry and spanned singleton pregnancies with estimated delivery dates from September 1, 2016 to March 31, 2021. The analysis revealed a risk, where increased NT measurements even that were less than 3.5 mm were linked with a increased likelihood of chromosomal anomalies beyond the most commonly screened conditions, such as trisomies 13, 18, 21 and sex chromosome abnormalities.
The study showed an adjusted risk ratio (ARR) of chromosomal anomalies at an alarming 20.33, with an adjusted risk difference (ARD) of 9.94% for the pregnancies with NT measurements between 3.0 and less than 3.5 mm. Also, when the analysis was restricted to less common chromosomal anomalies, the ARR was at 4.97 and the ARD was at 1.40% that underscored a significant increase in risk even for anomalies not routinely included in prenatal screening programs.
These findings were analyzed between March and August 2023 that challenged the adequacy of the current 3.5 mm NT cutoff and also illuminate the need for a precise approach to prenatal screening. The pregnancies with NT measurements less than 2.0 mm showed the lowest risk that indicated lower NT measurements could serve as a reassuring indicator for expecting parents and healthcare providers.
Reference:
Bellai-Dussault, K., Dougan, S. D., Fell, D. B., Little, J., Meng, L., Okun, N., Walker, M. C., Armour, C. M., & Potter, B. K. (2024). Ultrasonographic Fetal Nuchal Translucency Measurements and Cytogenetic Outcomes. In JAMA Network Open (Vol. 7, Issue 3, p. e243689). American Medical Association (AMA). https://doi.org/10.1001/jamanetworkopen.2024.3689