Noninvasive prenatal screening is a long-established and widely used methodology to screen pregnancies for the most common prenatal chromosomal aneuploidies. Since 2017, positive result reports have typically included a positive predictive value to assist informed clinical decision-making. Positive predictive value is calculated based on an assay's sensitivity and specificity for a particular condition, and for the purpose of noninvasive prenatal screening, the aneuploidy's prevalence by maternal age, sometimes further adjusted by gestational age, are included in the calculation. Considering the ubiquitous use of positive predictive value by major noninvasive prenatal screeningproviders in the US, it is important to consider its limitations and consequent clinical implications. Here we discuss how the calculation of positive predictive value for screen positive results precludes the ability of positive predictive value to act as a risk metric that is accurate for and specific to an individual pregnancy, and suggest posttest risk based on the amount of target chromosome excess (Z-score-based posttest risk) as an alternative metric for consideration.

中文翻译：

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基于 Z 评分的后测风险作为阳性无创产前筛查后阳性预测值的替代风险指标


无创产前筛查是一种由来已久且广泛使用的方法，用于筛查最常见的产前染色体非整倍体。自 2017 年以来，阳性结果报告通常包括阳性预测值，以帮助做出明智的临床决策。阳性预测值是根据测定对特定情况的敏感性和特异性计算的，并且出于无创产前筛查的目的，非整倍体的患病率按产妇年龄计算，有时根据胎龄进一步调整，包括在计算中。考虑到美国主要的无创产前筛查提供者普遍使用阳性预测值，重要的是要考虑其局限性和随之而来的临床意义。在这里，我们讨论了筛查阳性结果的阳性预测值的计算如何排除阳性预测值作为准确且特定于个体妊娠的风险指标的能力，并根据目标染色体超量（基于 Z 评分的后测风险）建议后测风险作为考虑的替代指标。