Department of Ultrasound and Fetal Medicine, Centre Médico-Chirurgical et Obstétrical-Syndicat Inter-Hospitalier de la Communauté Urbaine de Strasbourg, Strasbourg, France.
Ultrasound Obstet Gynecol. 2009 Oct;34(4):404-9. doi: 10.1002/uog.6439.
Fetal biometric data are a major part of prenatal ultrasound screening in the general population. The aim of this study was to analyze the effect of choice of reference curve on the quality of screening for growth abnormalities, using a statistical tool based on Z-scores.
The biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) were measured in 9699 ultrasound scans during the second trimester (20-24 weeks of gestation) and 8100 scans during the third trimester (30-34 weeks of gestation). These biometric data were all transformed retrospectively into Z-scores, calculated using five reference curves: those published by Snijders and Nicolaides (1994), Chitty et al. (1994), Kurmanavicius et al. (1999) and Salomon et al. (2006), and curves used at our ultrasound unit generated from a sample of the local population. The Z-score distribution was compared with the expected normal distribution by calculation of the mean and SD, and using the Kolmogorov-Smirnov test. The sensitivity and specificity of each reference curve were calculated to determine the capacity of these curves to identify fetuses with measurements < 5(th) percentile or > 95(th) percentile for each parameter.
Most of the distribution curves determined from the Z-scores of the measurements taken differed significantly from a non-skewed standard normal curve (mean of 0 and SD of 1). In our population, the Chitty reference curves gave the best results for identifying fetuses with abnormal (< 5(th) percentile or > 95(th) percentile) BPD (sensitivity, 100%; specificity, 97.24%), HC (sensitivity, 96.07%; specificity, 98.89%) and FL (sensitivity, 96.46%; specificity, 98.80%). The best reference for AC was the Salomon curve (sensitivity, 72.25%; specificity, 99.64%).
Checking for good concordance between the study population and chosen reference data is a key initial step in quality control. Z-scores are a simple tool for evaluating the performance of each reference curve for a given population in order to optimize the sensitivity and specificity of screening for fetal growth abnormalities.
胎儿生物测量数据是一般人群产前超声筛查的重要组成部分。本研究旨在使用基于 Z 分数的统计工具分析选择参考曲线对生长异常筛查质量的影响。
在孕中期（20-24 周妊娠）测量了 9699 次超声扫描的双顶径（BPD）、头围（HC）、腹围（AC）和股骨长（FL），在孕晚期（30-34 周妊娠）测量了 8100 次扫描。这些生物测量数据均被 retrospective 转化为 Z 分数，使用 5 条参考曲线计算：Snijders 和 Nicolaides（1994 年）、Chitty 等人（1994 年）、Kurmanavicius 等人（1999 年）和 Salomon 等人（2006 年）发布的曲线，以及我们超声单位使用当地人群样本生成的曲线。通过计算平均值和标准差，并使用 Kolmogorov-Smirnov 检验，比较 Z 分数分布与预期正态分布。计算每个参考曲线的灵敏度和特异性，以确定这些曲线识别每个参数<第 5 百分位数或>第 95 百分位数的胎儿的能力。
从测量的 Z 分数确定的大多数分布曲线与非偏斜标准正态曲线（平均值为 0，标准差为 1）显著不同。在我们的人群中，Chitty 参考曲线在识别 BPD（灵敏度为 100%，特异性为 97.24%）、HC（灵敏度为 96.07%，特异性为 98.89%）和 FL（灵敏度为 96.46%，特异性为 98.80%）异常（<第 5 百分位数或>第 95 百分位数）的胎儿方面给出了最好的结果。AC 的最佳参考曲线是 Salomon 曲线（灵敏度为 72.25%，特异性为 99.64%）。
检查研究人群与所选参考数据之间的良好一致性是质量控制的关键初始步骤。Z 分数是一种简单的工具，可用于评估给定人群中每条参考曲线的性能，以优化胎儿生长异常筛查的灵敏度和特异性。
