Oxford Maternal and Perinatal Health Institute, Green Templeton College and Nuffield Department of Obstetrics and Gynaecology, University of Oxford, John Radcliffe Hospital, Oxford, UK.
Ultrasound Obstet Gynecol. 2012 Mar;39(3):266-73. doi: 10.1002/uog.10082.
To assess intra- and interobserver variability of fetal biometry measurements throughout pregnancy.
A total of 175 scans (of 140 fetuses) were prospectively performed at 14-41 weeks of gestation ensuring an even distribution throughout gestation. From among three experienced sonographers, a pair of observers independently acquired a duplicate set of seven standard measurements for each fetus. Differences between and within observers were expressed in measurement units (mm), as a percentage of fetal dimensions and as gestational age-specific Z-scores. For all comparisons, Bland-Altman plots were used to quantify limits of agreement.
When using measurement units (mm) to express differences, both intra- and interobserver variability increased with gestational age. However, when measurement of variability took into account the increasing fetal size and was expressed as a percentage or Z-score, it remained constant throughout gestation. When expressed as a percentage or Z-score, the 95% limits of agreement for intraobserver difference for head circumference (HC) were ± 3.0% or 0.67; they were ± 5.3% or 0.90 and ± 6.6% or 0.94 for abdominal circumference (AC) and femur length (FL), respectively. The corresponding values for interobserver differences were ± 4.9% or 0.99 for HC, ± 8.8% or 1.35 for AC and ± 11.1% or 1.43 for FL.
Although intra- and interobserver variability increases with advancing gestation when expressed in millimeters, both are constant as a percentage of the fetal dimensions or when reported as a Z-score. Thus, measurement variability should be considered when interpreting fetal growth rates.
评估整个孕期胎儿生物测量值的观察者内和观察者间变异性。
对 140 例胎儿的 175 次扫描（共 175 次扫描）进行前瞻性研究，确保整个孕期均匀分布。从 3 名经验丰富的超声医师中，一对观察者独立地为每个胎儿获取了一套重复的七项标准测量值。观察者内和观察者间的差异以测量单位（mm）、胎儿尺寸的百分比和特定孕周的 Z 分数表示。对于所有比较，均使用 Bland-Altman 图来量化一致性界限。
当使用测量单位（mm）表示差异时，观察者内和观察者间的变异性均随孕周增加而增加。然而，当测量变异性并以百分比或 Z 分数表示时，其在整个孕期保持不变。以百分比或 Z 分数表示时，头围（HC）的观察者内差异的 95%一致性界限为±3.0%或 0.67；腹围（AC）和股骨长（FL）分别为±5.3%或 0.90 和±6.6%或 0.94。相应的观察者间差异值分别为±4.9%或 0.99 用于 HC，±8.8%或 1.35 用于 AC，±11.1%或 1.43 用于 FL。
尽管当以毫米表示时，观察者内和观察者间的变异性随孕周的增加而增加，但当以胎儿尺寸的百分比表示或以 Z 分数表示时，它们是恒定的。因此，在解释胎儿生长速度时应考虑测量变异性。
