Snijders R J, Platt L D, Greene N, Carlson D, Krakow D, Gregory K, Bradley K
Department of Obstetrics and Gynecology, Cedars-Sinai Medical Center, Cedars-Sinai Medical Center Burns & Allen Research Institute, UCLA School of Medicine, Los Angeles, CA, USA.
Ultrasound Obstet Gynecol. 2000 Aug;16(2):142-5. doi: 10.1046/j.1469-0705.2000.00198.x.
This study assesses two methods used to define relatively short femur in screening for trisomy 21 and examines changes in performance of screening with gestational age.
Retrospective analysis of data on menstrual age, femur length (FL) and biparietal diameter (BPD) in 49 trisomy 21 pregnancies and 6069 normal controls. Reference ranges were derived for BPD/FL versus menstrual age and for FL versus BPD. Two methods of defining short femur (BPD/FL and observed-to-expected FL ratio) were examined for false-positive rates and detection rates for trisomy 21 at different gestational ages.
In the control group the BPD/FL ratio and its standard deviation decreased with menstrual age. Trisomy 21 was associated with a significantly higher BPD/FL ratio (P < 0.001) and the deviation increased significantly with menstrual age (P < 0.05). Eleven percent of 28 fetuses examined at 15-17 weeks had a BPD/FL above the 95th centile compared with 24% of 21 fetuses examined at 18-20 weeks (P = 0.40). The median observed-to-expected FL ratio in the control group was 1.0 throughout the gestational age range but the standard deviation decreased significantly with menstrual age (P < 0.01). Trisomy 21 was associated with a significantly reduced observed-to-expected FL ratio (P < 0.001) and the deviation increased significantly with menstrual age (P < 0.05). A fixed cut-off of 0.91 for observed-to-expected FL ratio provided a false-positive rate of 12% at 15-17 weeks compared with 6% at 18-20 weeks of gestation (P < 0.001) with detection rates of 29 and 38%, respectively (P = 0.73).
Irrespective of the definition used to define the condition, relatively short femur is a poor marker for trisomy 21 particularly when the assessment takes place before 18 weeks of gestation.
本研究评估了在筛查21三体综合征时用于定义相对短股骨的两种方法，并研究了筛查性能随孕周的变化。
对49例21三体妊娠和6069例正常对照的月经年龄、股骨长度（FL）和双顶径（BPD）数据进行回顾性分析。得出了BPD/FL与月经年龄以及FL与BPD的参考范围。研究了两种定义短股骨的方法（BPD/FL和观察到的与预期的FL比值）在不同孕周时21三体综合征的假阳性率和检出率。
在对照组中，BPD/FL比值及其标准差随月经年龄下降。21三体综合征与显著更高的BPD/FL比值相关（P<0.001），且该偏差随月经年龄显著增加（P<0.05）。在15 - 17周检查的28例胎儿中，11%的胎儿BPD/FL高于第95百分位数，而在18 - 20周检查的21例胎儿中这一比例为24%（P = 0.40）。对照组中观察到的与预期的FL比值中位数在整个孕周范围内均为1.0，但标准差随月经年龄显著下降（P<0.01）。21三体综合征与显著降低的观察到的与预期的FL比值相关（P<0.001），且该偏差随月经年龄显著增加（P<0.05）。观察到的与预期的FL比值固定截断值为0.91时，在15 - 17周时假阳性率为12%，而在妊娠18 - 20周时为6%（P<0.001），检出率分别为29%和38%（P = 0.73）。
无论用于定义该情况的定义如何，相对短股骨对于21三体综合征都是一个较差的标志物，尤其是在妊娠18周之前进行评估时。
