How imprecise may the measurement of fetal nuchal translucency be without worsening the firsttrimester screening?

P. Schmidt; I. Staboulidou; C. Hörmansdörfer; M. Elsässer; P. Hillemanns; A. Scharf

doi:10.1055/s-2007-988938

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Ultraschall Med 2007; 28 - V_3_27
DOI: 10.1055/s-2007-988938

How imprecise may the measurement of fetal nuchal translucency be without worsening the firsttrimester screening?

P Schmidt ¹, I Staboulidou ¹, C Hörmansdörfer ¹, M Elsässer ², P Hillemanns ¹, A Scharf ²

¹Medical University of Hannover, Department of Obstetrics and Gynecology, Hannover, Germany
²University of Heidelberg, Department of Obstetrics and Gynecology, Heidelberg, Germany

Congress Abstract

Objective: The firsttrimester screening (FTS) has a trisomy 21 detection rate of about 90%. Despite a profound training, the pracitically reached measurement quality of the nuchal translucency (NT) is probably not optimal. This study investigated the impact of measurement errors on the FTS.

Methods: The data of 10116 combined FTSs had been acquired in a multicenter study. Risk assessment was performed by the JOY software in accordance to Nicolaides. To investigate the impact of measurement errors, the NT values were artificially altered and the adjusted risks were recalculated. Test performance parameters were obtained and compared to the correct measurements.

Results: In this study 85 fetuses were gentically affected. The screening was wrongly unsuspicious in 12 cases and in 479 cases the FTS resulted false positive. An assumed NT error of±0.1mm already causes a high significant change of the false positive rate. A difference of -0.2mm leads to a visible change of the false negatives.

Discussion: This study demonstrates that even by smallest deviations the false negative rate will be significantly affected. The detection of really diseased fetuses is influenced at -0.2mm measurement error. Therefor the NT measuremtent has to be as precise as any possible.