Department of Obstetrics and Gynecology, St Antonius Hospital, Nieuwegein, Utrecht, The Netherlands.
Ultrasound Obstet Gynecol. 2012 Feb;39(2):185-90. doi: 10.1002/uog.9047. Epub 2011 Dec 5.
To study the ratio of prenasal thickness (PT) to nasal bone length (NBL) in normal and trisomy-21 fetuses in the second and third trimesters of pregnancy.
The PT and NBL were measured retrospectively in 106 normal fetuses (in three-dimensional (3D) volumes) and in 30 fetuses with trisomy 21 (10 on two-dimensional (2D) images and 20 in 3D volumes).
In normal fetuses the mean PT and NBL increased between 15 and 33 weeks' gestation from 2.3 to 6.1 mm (r = 0.85, P < 0.001) and from 3.3 to 9.6 mm (r = 0.87, P < 0.001), respectively. The PT : NBL ratio was stable throughout gestation, with a mean of 0.61 (95% CI, 0.59-0.63; r = - 0.04, P = 0.7). The 5(th) and 95(th) percentiles were 0.48 and 0.80, respectively. In trisomy-21 fetuses the mean PT and NBL increased between 14 and 34 weeks from 3.0 to 9.2 mm (r = 0.86, P < 0.001) and from 1.9 to 7.8 mm (r = 0.85, P < 0.001), respectively. The PT : NBL ratio was significantly higher than in normal fetuses (P < 0.001) but also stable throughout gestation, with a mean of 1.50 (95% CI, 1.20-1.80; r = - 0.35, P = 0.07). Twenty-three (77%) of the 30 fetuses with trisomy 21 had a PT above the 95(th) percentile and 20 (67%) had an NBL below the 5(th) percentile. All the trisomy-21 fetuses had a PT : NBL ratio above the 95(th) percentile. When the 95(th) percentile of the PT : NBL ratio was used as a cut-off value the detection and false positive rates for trisomy 21 were 100 (95% CI, 89-100)% and 5 (95% CI, 2-11)%, respectively. The positive likelihood ratio was 21.2.
The PT : NBL ratio is stable in the second and third trimesters of pregnancy in both normal and trisomy-21 fetuses, but all trisomy-21 fetuses in this series had a PT : NBL ratio above the 95(th) percentile. The ratio is therefore a strong marker for trisomy 21.
研究正常妊娠和 21 三体胎儿在妊娠第二和第三 trimester 中鼻前厚度（PT）与鼻骨长度（NBL）的比值。
回顾性测量了 106 例正常胎儿（三维容积）和 30 例 21 三体胎儿（二维图像 10 例，三维容积 20 例）的 PT 和 NBL。
在正常胎儿中，PT 和 NBL 在 15 至 33 周妊娠期间分别从 2.3 至 6.1mm（r=0.85，P<0.001）和从 3.3 至 9.6mm（r=0.87，P<0.001）增加。PT：NBL 比值在整个妊娠期间保持稳定，平均值为 0.61（95%置信区间，0.59-0.63；r=-0.04，P=0.7）。第 5 百分位数和第 95 百分位数分别为 0.48 和 0.80。在 21 三体胎儿中，PT 和 NBL 分别从 14 至 34 周妊娠期间从 3.0 至 9.2mm（r=0.86，P<0.001）和从 1.9 至 7.8mm（r=0.85，P<0.001）增加。PT：NBL 比值明显高于正常胎儿（P<0.001），但在整个妊娠期间也保持稳定，平均值为 1.50（95%置信区间，1.20-1.80；r=-0.35，P=0.07）。30 例 21 三体胎儿中有 23 例（77%）PT 值高于第 95 百分位数，20 例（67%）NBL 值低于第 5 百分位数。所有 21 三体胎儿的 PT：NBL 比值均高于第 95 百分位数。当 PT：NBL 比值的第 95 百分位数用作截断值时，21 三体的检测和假阳性率分别为 100%（95%置信区间，89-100）和 5%（95%置信区间，2-11）。阳性似然比为 21.2。
在正常妊娠和 21 三体胎儿中，PT：NBL 比值在妊娠第二和第三 trimester 均保持稳定，但本系列中所有 21 三体胎儿的 PT：NBL 比值均高于第 95 百分位数。因此，该比值是 21 三体的一个强有力的标志物。
