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© 2004 by the American Institute of Ultrasound in Medicine
J Ultrasound Med 23:1613-1618 • 0278-4297

Reproducibility of the Fetal Nasal Bone Length Measurement

Mireille N. Bekker, MD, Jos W. R. Twisk, PhD and John M. G. van Vugt, MD, PhD

Departments of Obstetrics and Gynecology (M.N.B., J.M.G.v.V.) and Clinical Epidemiology and Biostatistics (J.W.R.T.), Vrije Universiteit Medical Center, Amsterdam, the Netherlands.

Address correspondence and reprint requests to Mireille N. Bekker, MD, Vrije Universiteit Medical Center, Stafgebouw L-348, de Boelelaan 1117, 1081 HV Amsterdam, the Netherlands. E-mail: mn.bekker{at}vumc.nl.

Objective. To investigate the reproducibility of the fetal nasal bone length measurement in the first trimester. Methods. In this prospective study, crown-rump length, nuchal translucency, and nasal bone length were measured in 90 singleton pregnancies between 11 and 14 weeks of pregnancy. The study was divided into 2 equal substudies. Three investigators measured the nasal bone in study I. After an intensive 3-month training program, the same 3 investigators measured the nasal bone in study II. Measurement of the nasal bone was standardized. All investigators were blinded and measured the nasal bone 3 times. The intraclass correlation coefficient (intra-CC) and interclass correlation coefficient (inter-CC) were calculated. Results. Nasal bone length measurement was successfully performed in all cases. The median nasal bone lengths were 2.3 (range, 1.5–3.2), 2.6 (range, 1.4–4.2), and 2.9 (range, 2.1–3.8) mm between 77 and 83, 84 and 90, and 91 and 98 days’ gestational age, respectively; median crown-rump length was 63.0 (range, 45.0–83.3) mm; and median nuchal translucency measurement was 1.3 (range, 0.9–2.5) mm. The correlation between the 3 observers was poor (inter-CC, 0.32) in the first study. After the training program, the interobserver correlation improved but was still moderate (inter-CC, 0.64). In both studies the interobserver variability did not differ between 11, 12, and 13 weeks’ gestational age. There was no relationship between the mean nasal bone length and interobserver difference in both studies. The intraobserver variability was good for each investigator in both studies (intra-CC: study I, 0.93, 0.95, and 0.97; study II, 0.98, 0.97, and 0.97, respectively). Conclusions. This study shows that the reproducibility of the fetal nasal bone length measurement in the first trimester is inadequate.

Key Words: Down syndrome • nasal bone length • prenatal • reproducibility • sonography

Abbreviations: CRL, crown-rump length • inter-CC, interclass correlation coefficient • intra-CC, intraclass correlation coefficient • NT, nuchal translucency

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