Salomon L J, Bernard J P, Duyme M, Buvat I, Ville Y
Service de Gynécologie-Obstétrique, Centre Hospitalier Intercommunal de Poissy-St Germain, Poissy, France.
Ultrasound Obstet Gynecol. 2005 Jun;25(6):559-65. doi: 10.1002/uog.1901.
The assessment of fetal biometry is usually based on the comparison of measured values with predicted values derived from reference charts or equations in a normal population. This study was undertaken to assess the impact of the choice of reference charts and to develop a Z-score-based tool that could help sonographers to choose the reference charts that best fit their practice.
Fetal biparietal diameter, head circumference, abdominal circumference and femur diaphysis length measurements were made at 20-24 and 30-34 weeks' gestation by four experienced sonographers. All measurements were transformed into Z-scores calculated according to three prediction equations (Snijders and Nicolaides, 1994; Chitty et al., 1994 and Kurmanavicius et al., 1999). Distributions of Z-scores were compared to the expected standard normal distribution based on mean, SD and Kolmogorov-Smirnov test. Simulations were made to assess sensitivity (Se), specificity (Sp) and Youden's index (Se + Sp - 1) of each reference equation, reflecting their ability to identify fetuses with abnormal biometry in our population. The reference that best fitted our practice was determined based on these results.
The Z-scores of all biometric parameters were significantly different (P < 0.001) when using any of the three reference equations, and none of the Z-score distributions could be considered similar to the standard normal distribution. The number of measurements that would be considered as abnormal according to these references ranged from 2.6% to 23.6%. Se and Sp ranged from 39.59% to 67.12% and 90.14% to 99.69%, respectively.
Assessment of fetal biometry is largely dependent on the choice of reference charts. We suggest that the choice of reference charts for fetal biometry could be controlled using Z-scores in each institution and that this could be the first step towards any quality assessment policy. The method we describe for the choice of the most appropriate fetal biometry reference chart might be used for all size charts.
胎儿生物测量评估通常基于将测量值与从正常人群参考图表或公式得出的预测值进行比较。本研究旨在评估参考图表选择的影响，并开发一种基于Z评分的工具，以帮助超声检查人员选择最适合其实际操作的参考图表。
由四名经验丰富的超声检查人员在妊娠20 - 24周和30 - 34周时测量胎儿双顶径、头围、腹围和股骨干长度。所有测量值均根据三个预测方程（斯奈德和尼古拉ides，1994年；奇蒂等人，1994年；库马纳维丘斯等人，1999年）转换为Z评分。基于均值、标准差和柯尔莫哥洛夫-斯米尔诺夫检验，将Z评分分布与预期的标准正态分布进行比较。进行模拟以评估每个参考方程的敏感性（Se）、特异性（Sp）和尤登指数（Se + Sp - 1），反映它们在我们的人群中识别生物测量异常胎儿的能力。根据这些结果确定最适合我们实际操作的参考标准。
使用三个参考方程中的任何一个时，所有生物测量参数的Z评分均有显著差异（P < 0.001），且没有一个Z评分分布可被认为与标准正态分布相似。根据这些参考标准被视为异常的测量次数在2.6%至23.6%之间。Se和Sp分别在39.59%至67.12%和90.14%至99.69%之间。
胎儿生物测量评估在很大程度上取决于参考图表的选择。我们建议在每个机构中使用Z评分来控制胎儿生物测量参考图表的选择，这可能是迈向任何质量评估政策的第一步。我们描述的选择最合适胎儿生物测量参考图表的方法可能适用于所有尺寸图表。
