Reproducibility study of crown-rump length and biparietal diameter measurements in the first trimester

Abstract

Objective: This study aims to investigate the intra‐observer and inter‐observer variability of crown–rump length (CRL) and biparietal diameter (BPD) measurements in the first trimester. Methods: A prospective observational study on 592 fetuses between 8 and 14 gestational weeks was conducted. Intra‐class correlation coefficients (ICCs) were computed, and Bland–Altman analysis was carried out. Results: The ICCs (95% confidence interval) and the 95% limits of agreement, expressed as a percentage of the average, for CRL's intra‐observer and inter‐observer variability were 0.979 (0.974–0.982, p < 0.001), +8.53% to −8.376%, and 0.968 (0.952–0.978, p < 0.001), +9.06% to −7.69%, respectively. The corresponding figures for BPD were 0.981 (0.977–0.984, p < 0.001), +7.41% to −7.51%, and 0.968 (0.952–0.978, p < 0.001), +6.65% to −7.25%. After conversion in days, the ICCs and 95% limits of agreement for CRL's intra‐observer and inter‐observer variability were 0.983 (0.980–0.986, p < 0.001), +2.88% to −2.84%, and 0.971 (0.957–0.980, p < 0.001), 2.83% to −2.60%, respectively. The corresponding figures for BPD were 0.982 (0.979–0.986, p < 0.001), +3.36% to −3.40%, and 0.968 (0.953–0.978, p < 0.001), +3.06% to −3.38%. CRL's standard deviation of the differences increased with gestation for intra‐observer (r = 0.289, p < 0.001) and inter‐observer (r = 0.197, p = 0.023) variability. Conclusion: The BPD and CRL are highly reproducible measurements. CRL's measurement error increased with the magnitude of CRL, whereas BPD's reproducibility was not affected by gestational age. © 2012 John Wiley & Sons, Ltd.