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Nasal bone length: prenasal thickness ratio: a strong 2D ultrasound marker for Down syndrome
Andrea Szabó1, Károly Szili, János Tamás Szabó
1MEDISONO Fetal and Adult Health Research Center, Szeged, Hungary; Department of Medical Genetics, University of Szeged, Szeged, Hungary.
Objectives:
To evaluate the feasibility of incorporating two-dimensional ultrasound measurements of nasal bone length (NBL) and prenasal thickness (PT) into the second-trimester anomaly scan and to determine whether the NBL : PT ratio could help in differentiating euploid and Down syndrome fetuses.
Method:
Two-dimensional measurements of NBL and PT were obtained from the midsagittal plane of the fetal head at 14-28 weeks of gestation in a Caucasian population at risk for aneuploidy. The screening performances of NBL, PT, and the ratios NBL : PT and PT : NBL were analyzed in euploid (n = 1330) and Down syndrome (n = 33) fetuses.
Results:
Nasal bone length and PT alone showed strong correlations with Down syndrome (sensitivity: 76% at 1.88% and 2.35% false positive rate, respectively). However, the NBL : PT ratio showed an even stronger correlation with Down syndrome (false positive rate: 0.9%, sensitivity: 97%). The mean NBL : PT ratio showed a gradual increase from 1.48 to 1.79 (a 21.2% increase) between 14 and 28 weeks of gestation.
Conclusion:
Two-dimensional ultrasound measurements of NBL and PT, particularly the NBL : PT ratio, are highly sensitive markers for Down syndrome fetuses.
