Department of Obstetrics and Gynecology, University of Tuebingen, Tuebingen, Germany.
Ultrasound Obstet Gynecol. 2010 May;35(5):525-9. doi: 10.1002/uog.7599.
Screening for trisomy 21 by fetal nuchal translucency (NT) thickness at 11 to 13 + 6 weeks' gestation requires an appropriate examination of the NT. Errors in the assessment of NT may lead to an under- or overestimation of the NT and to incorrect patient-specific risks. In this study we aimed to examine the importance of the mid-sagittal section and whether the acquired plane of the head and face influences the measurement of the fetal NT thickness.
Sixty three-dimensional volumes of the fetal head and face in a mid-sagittal plane were acquired. NT thickness was firstly measured in the mid-sagittal plane according to the guidelines of The Fetal Medicine Foundation. The head was then rotated by steps of 5 degrees up to 25 degrees around the mid-point of the biparietal diameter and occipitofrontal diameter and NT was measured again. All six NT measurements were taken by the same operator, Operator A, who on completion of the assessment of the 60 volumes repeated all the measurements. The whole process was then repeated by Operator B. Both operators were blinded to each others' measurements.
In the true mid-sagittal plane, the mean NT was 1.9 mm and it was above the expected median in 72.5% of the measurements. At a deviation of 15 degrees , mean NT was 1.5 mm, and 36.3% of the measurements were above the expected median. At a deviation of 25 degrees , mean NT was reduced to 1.3 mm and 17.9% of the measurements were above the expected median.
Fetal NT thickness is greatest in the mid-sagittal plane. Increasing deviation away from the mid-sagittal plane results in progressive underestimation of the fetal NT thickness and so to a corresponding underestimation of the patient-specific risk.
通过在 11 至 13+6 孕周时对胎儿颈项透明层（NT）厚度进行检测，筛查 21 三体。对 NT 进行评估时的误差可能导致 NT 的低估或高估，以及对患者特异性风险的错误估计。本研究旨在检查正中矢状切面的重要性，以及头面部获取的切面是否会影响胎儿 NT 厚度的测量。
获取 63 例胎儿头面部正中矢状切面的三维容积。首先根据胎儿医学基金会的指南在正中矢状切面上测量 NT 厚度。然后，头以双额径和枕额径中点为中心，以 5 度为一个单位向上旋转 25 度，再次测量 NT。所有 6 个 NT 测量均由同一位操作人员（Operator A）进行，Operator A 在完成 60 个容积的评估后，重复所有测量。然后由另一位操作人员（Operator B）重复整个过程。两位操作人员均不知道彼此的测量结果。
在真正的正中矢状切面上，平均 NT 为 1.9mm，其中 72.5%的测量值高于预期中位数。在 15 度偏差时，平均 NT 为 1.5mm，其中 36.3%的测量值高于预期中位数。在 25 度偏差时，平均 NT 降低至 1.3mm，其中 17.9%的测量值高于预期中位数。
胎儿 NT 厚度在正中矢状切面上最大。从正中矢状面偏离程度增加，导致胎儿 NT 厚度逐渐低估，从而导致患者特异性风险相应低估。
