Smith-Bindman R, Hosmer W, Feldstein V A, Deeks J J, Goldberg J D
Department of Radiology, University of California, San Francisco, 1600 Divisadero St, San Francisco, CA 94115, USA.
JAMA. 2001 Feb 28;285(8):1044-55. doi: 10.1001/jama.285.8.1044.
Second-trimester prenatal ultrasound is widely used in an attempt to detect Down syndrome in fetuses, but the accuracy of this method is unknown.
To determine the accuracy of second-trimester ultrasound in detecting Down syndrome in fetuses.
English-language articles published between 1980 and February 1999 identified through MEDLINE and manual searches.
Studies were included if they recorded second-trimester findings of ultrasonographic markers, chromosomal abnormalities, and clinical outcomes for a well-described sample of women. A total of 56 articles describing 1930 fetuses with Down syndrome and 130 365 unaffected fetuses were included.
Articles were independently reviewed, selected, and abstracted by 2 reviewers. Discrepancies in data abstraction were resolved by consensus with a third reviewer. Overall estimates of sensitivity, specificity, and positive and negative likelihood ratios were calculated for the following markers: choroid plexus cyst, thickened nuchal fold, echogenic intracardiac focus, echogenic bowel, renal pyelectasis, and humeral and femoral shortening. Results were stratified by whether markers were identified in isolation or in conjunction with fetal structural malformations.
When ultrasonographic markers were observed without associated fetal structural malformations, sensitivity for each was low (range, 1%-16%), and most fetuses with such markers had normal outcomes. A thickened nuchal fold was the most accurate marker for discriminating between unaffected and affected fetuses and was associated with an approximately 17-fold increased risk of Down syndrome. If a thickened nuchal fold is used to screen for Down syndrome, 15 893 average-risk women or 6818 high-risk women would need to be screened for each case of Down syndrome identified. For each of the other 6 markers, when observed without associated structural malformations, the marker had marginal impact on the risk of Down syndrome. Because the markers were detected in only a small number of affected fetuses, the likelihood of Down syndrome did not decrease substantially after normal examination findings (none of the negative likelihood ratios were significant).
A thickened nuchal fold in the second trimester may be useful in distinguishing unaffected fetuses from those with Down syndrome, but the overall sensitivity of this finding is too low for it to be a practical screening test for Down syndrome. When observed without associated structural malformations, the remaining ultrasonographic markers could not discriminate well between unaffected fetuses and those with Down syndrome. Using these markers as a basis for deciding to offer amniocentesis will result in more fetal losses than cases of Down syndrome detected, and will lead to a decrease in the prenatal detection of fetuses with Down syndrome.
孕中期产前超声被广泛用于尝试检测胎儿唐氏综合征，但该方法的准确性尚不清楚。
确定孕中期超声检测胎儿唐氏综合征的准确性。
通过医学文献数据库（MEDLINE）检索和手工检索，获取1980年至1999年2月发表的英文文章。
如果研究记录了孕中期超声标志物的检查结果、染色体异常情况以及对描述详细的一组孕妇的临床结局，则纳入该研究。共纳入56篇文章，描述了1930例患有唐氏综合征的胎儿和130365例未受影响的胎儿。
由2名审阅者独立对文章进行审阅、选择和摘要。数据摘要中的差异通过与第三名审阅者达成共识来解决。计算了以下标志物的敏感性、特异性、阳性似然比和阴性似然比的总体估计值：脉络丛囊肿、颈部褶皱增厚、心内强回声光斑、肠管强回声、肾盂扩张以及肱骨和股骨短小。结果根据标志物是单独发现还是与胎儿结构畸形同时发现进行分层。
当超声标志物单独出现而无相关胎儿结构畸形时，每个标志物的敏感性都很低（范围为1% - 16%），大多数有此类标志物的胎儿结局正常。颈部褶皱增厚是区分未受影响胎儿和受影响胎儿最准确的标志物，与唐氏综合征风险增加约17倍相关。如果使用颈部褶皱增厚来筛查唐氏综合征，每发现一例唐氏综合征病例，平均需要筛查15893名平均风险孕妇或6818名高风险孕妇。对于其他6种标志物中的每一种，当单独出现而无相关结构畸形时，该标志物对唐氏综合征风险的影响很小。由于仅在少数受影响胎儿中检测到这些标志物，正常检查结果后唐氏综合征的可能性并未大幅降低（所有阴性似然比均无统计学意义）。
孕中期颈部褶皱增厚可能有助于区分未受影响的胎儿和患有唐氏综合征的胎儿，但这一发现的总体敏感性过低，无法作为唐氏综合征的实际筛查试验。当单独出现而无相关结构畸形时，其余超声标志物无法很好地区分未受影响的胎儿和患有唐氏综合征的胎儿。以这些标志物为基础决定是否进行羊膜穿刺术，将导致更多的胎儿丢失，而检测出的唐氏综合征病例数却很少，并会导致唐氏综合征胎儿的产前检测率下降。
