不同颈项透明层厚度中位数对孕早期唐氏筛查效能的影响

Effect of different nuchal translucency thickness medians on Down’s syndrome screening efficacy in first-trimester

目的探讨不同颈项透明层(NT)厚度中位数对孕早期唐氏综合征筛查效能的影响。方法选择我院产前诊断中心11位具有孕早期NT检查资格的超声医师,对23 446例单胎妊娠孕妇行NT筛查。NT测值通过英国胎儿医学基金会(FMF)推荐预期中位数转换为NT中位数的倍数(NT-Mom),监测超声医师测量的NT-Mom中位数是否位于0.9~1.1,按NT-Mom中位数所属区间将超声医师分为测量不足组(NT-Mom<0.9)、在控组(NT-Mom 0.9~1.1)、测量过度组(NT-Mom>1.1)。再分别用本地中心特有的和NT测量操作者特有的中位数将NT值转换为NT-Mom,观察各组测得的NT-Mom数据分布情况,评估其对唐氏综合征的筛查效能。应用指数加权移动平均(EWMA)质控图分析各组失控率;应用多元Logistic回归分析FMF中位数筛查唐氏综合征的假阳性率与其相关影响因素的关系。结果 23 446例胎儿中,21-三体综合征胎儿57例,NT中位数3.40 mm;18-三体综合征胎儿24例,NT中位数5.40 mm;13-三体综合征胎儿6例,NT中位数2.00 mm;Turner综合征23例,NT中位数5.60 mm;其他染色体异常胎儿10例,NT中位数2.25 mm。11位超声医师中,测量不足组2位,在控组6位,测量过度组3位。测量不足组和测量过度组的NT测值使用本地中心特有的中位数转换为NT-Mom后,其中位数所在区间属性不变;而使用操作者特有的中位数转换后,其NT-Mom中位数回归0.9~1.1。唐氏综合征风险截断值为1∶250时,FMF、本地中心特有及操作者特有NT中位数对唐氏综合征的检出率分别为77.19%、77.19%、78.95%,差异无统计学意义;假阳性率分别为6.58%、6.23%、6.43%,差异有统计学意义(P<0.05)。多元Logistic回归分析显示,以唐氏综合征筛查风险值1∶250为截断值,FMF中位数的假阳性率与操作者特有的NT-Mom、EWMA失控率及妊娠年龄均有关,OR值分别为453.72(95%CI:108.05~1922.97)、1.39(95%CI:1.10~1.75)、1.30(95%CI:1.28~1.31)。结论使用NT操作者特有的中位数可一定程度上降低NT测量结果的变异性,提高NT测值对唐氏综合征的筛查效能,保持适当的NT筛查效能需要持续监测超声操作者的检测质量。

Objective To investigate the effect of different nuchal translucency thickness(NT) thickness medians on screening efficacy for Down’s syndrome in first-trimester.Methods Eleven NT credentialed sonographers of the prenatal diagnosis center in our hospital were picked out,who conducted NT scans on 23 446 cases of singleton pregnancies in firsttrimester.NT measurements were firstly transformed into multiply of NT median(NT-Mom) by the expected medians from the recommendation of Fetal Medicine Foundation(FMF) in order to survey whether the median NT-Mom measured by sonographers was in the range of 0.9~1.1.The sonographers were grouped three categories,including <0.9 undermeasuring group,0.9~1.1 incontrol group,and>1.1 overmeasuring group in terms of their medians.Then local center-specific or practitioner-specific medians were used to convert NT measurements into NT-Mom.The changes of NT-Mom distributions from the three different categories were investigated and their performance of NT screening for Down’s syndrome were also evaluated.Furthermore,out of control rate of ultrasound practitioner were calculated by exponentially weighted moving average(EWMA) chart for NT quality.Multiple Logistic regression was applied to analyze the correlation between the false positive rate of FMF median and its related influencing factors.Results In 23 446 fetuses,NT median was 3.40 mm for 57 fetuses affected by trisomy 21 syndrome,5.40 mm for 24 fetuses affected by trisomy 18 syndrome,2.00 mm for 6 fetuses affected by trisomy 13 syndrome,5.60 mm for 23 fetuses affected by Turner’s syndrome,2.25 mm for 10 fetuses affected by other chromosome abnormalities,respectively.Among 11 sonographers,there were 2 sonographers classified as undermeasuring group,6 as in-control group,3 as overmeasuring group.NT-Mom medians in both undermeasruing group and overmeasuring groups after using local center-specific NT medians still stayed in the original interval,whereas their NT-Mom medians transformed with practitioner-specific NT medians returned into 0.9~1.1.The detection rates of Down’s syndrome using FMF,local central-specific and practitioner-specific NT median were77.19%,77.19% and 78.95%,respectively,with no statistically significant difference at a risk cutoff value as 1:250,but the false positive rate were 6.58%,6.23%,6.43%,which were significantly different(P<0.05).Multiple Logistic regression analysis demonstrated that with a risk cutoff value as 1:250,the false positive rate of FMF median was associated with practitionerspecific NT medians,out of control rate of EWMA,and gestational age and OR were 453.7(95%CI:108.05~1922.97),1.39(95%CI:1.10~1.75) and 1.30(95%CI:1.28~1.31),respectively.Conclusion Utilization of practitioner-specific NT medians to a certain extent reduces variation of NT value and improves the screening performance for Down’s syndrome.Maintaining the appropriate performance of NT screening requires continuous supervision of NT measurement quality from sonographers.