Measuring Up Before Birth: The New Normal.
Measuring Up Before Birth: The New Normal.
复制标题
出生前测量：新常态。
DOI：
10.1161/circimaging.118.008008
复制
发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Peyvandi,Shabnam
中科院分区：
文献类型：
--
作者：
Moon-Grady,AnitaJ;Peyvandi,Shabnam
用于疾病检测的胎儿超声心动图具有挑战性。不仅存在技术障碍（仅举几例），例如母体体型、多变且常常不利的胎位等，而且在大多数产科和许多心脏病学实践中，绝大多数胎儿都是正常的。由于危险因素，大量患者被转介进行心脏成像，作为常规筛查的一部分，或者在异常筛查（例如颈项透明层超过 95%）之后；只有一小部分会出现异常。除此之外，由于胎儿分流的存在以及胎儿胎盘循环在保持氧气输送在正常范围内的同时改变血流方向的能力，几乎所有胎儿心脏异常在胎儿生命中都是无症状的。因此，细微的异常很容易被忽视，主观上几乎没有异常的瓣膜或血管可能会在繁忙的诊所中错误地通过检查，或者被认为是操作员甚至胎儿的不良形象。但随着几十年来成像平台和操作员专业知识的不断提高，我们也认识到，即使是妊娠早期到中期与正常情况明显微小的偏差也可能对新生儿产生可怕的后果，即使对于看似微小的病变，准确、精确地分配正常与异常值的需求也正在成为主流。 1 然而，胎儿超声心动图技师在这里遇到了另一个问题，即在整个妊娠期间判断胎儿心脏结构尺寸的尺子不断变化的问题。幸运的是，这个问题对于儿科心脏病专家来说很熟悉：心脏结构随患者体型的不同而变化，而患者体型的变化也随着患者年龄的变化而变化，其方式可预测、可建模。表达给定患者的瓣膜和血管尺寸的最常见方法是将测量值转换为 Z 分数或高于或低于相似规模人群的预期平均值的 SD 数量。在实践中，一旦为正常人群的一组测量值定义了最佳拟合关系，就可以得出每个体型点的标准差和平均值。尽管概念看似简单，但心脏人体测量的行为使得正态分布可能因不同患者体型而异，尤其是在极端情况下；称为异方差性的属性。因此，为了对正常范围有信心，在生成正常值方程时，每种体型的患者数量都必须相当大。胎儿的体重无法直接测量，而是通过线性测量来估计。如果孕龄已知，则可用于推断胎儿体重；然而，值得注意的是，胎儿的大小随胎龄的不同而变化，并且胎儿存在一系列正常的身体大小，这是一种具有其固有异方差性的衡量标准。 2
Fetal echocardiography for disease detection is challenging. Not only are there technical obstacles—maternal body habitus, variable and often unfavorable fetal position, to name a few—but in most obstetric and many cardiology practices, the vast majority of fetuses will be normal. Large numbers are referred for cardiac imaging either as part of routine screening because of risk factors or after an abnormal screen, such as nuchal translucency above 95th percentile; only a small subset will be abnormal. Add to this that nearly all fetal cardiac abnormalities are asymptomatic in fetal life because of the presence of the fetal shunts and the ability of the fetoplacental circulation to redirect flow while maintaining oxygen delivery in a normal range. Hence, a subtle abnormality becomes easy to overlook, a valve or vessel that is just barely subjectively abnormal may incorrectly pass muster in a busy clinic or be passed off as a poor image blamed on the operator or even the fetus. But as imaging platforms and operator expertise have been improving over the decades, so too has our understanding that even apparently minor deviations from normal in early to mid-gestation may have dire consequences for the newborn and the need to accurately and precisely assign a value of normal versus abnormal even for seemingly minor lesions is moving into mainstream. 1 Here, though, the fetal echocardiographer encounters another issue, that of the constantly changing ruler by which to judge the fetal cardiac structure dimensions throughout gestation. Luckily, this issue is familiar to pediatric cardiologists: cardiac structures vary with patient size, and patient size varies with patient age in predictable, model-able ways. The most common method for expressing a given patient’s valve and vessel dimensions is to transform a measurement to a Z score or the number of SDs above or below the expected mean value for a population of similar size. In practice, once a best-fit relationship is defined for a set of measurements from the normal population, an SD and mean can be derived at each body size point. Although seemingly simple in concept, the behavior of cardiac anthropometric measurements is such that the normal distribution may vary at different patient sizes, especially at extremes; a property termed heteroscedasticity. Therefore, to have confidence in a normal range, a fairly large number of patients at each body size is necessary when generating normal value equations. In the fetus, weight is not directly measurable but rather estimated from linear measurements. If gestational age is known, it can be used to extrapolate the fetal weight; however, it is important to note that fetal size varies with gestational age and that there is a range of normal body sizes in the fetus, a measure with its own innate heteroscedasticity. 2