Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
Ultrasound Obstet Gynecol. 2010 Nov;36(5):542-7. doi: 10.1002/uog.7663.
This study was carried out to examine the performance of a contingent policy in first-trimester screening for trisomy 21, in which the estimated risk was first derived by a combination of maternal age, fetal nuchal translucency (NT) thickness, presence/absence of the nasal bone, blood flow in the ductus venosus or flow across the tricuspid valve, and biochemical testing was carried out only in those who were found to have an intermediate risk. We also examined the performance of a policy in which the estimated risk was first derived by a combination of maternal age and biochemical testing, and ultrasound examination was carried out only in those with an intermediate risk.
The data for this study were derived from prospective screening for trisomy 21 in singleton pregnancies, using, as markers, a combination of maternal age, fetal NT thickness and maternal-serum free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A), in a one-stop clinic for first-trimester assessment of risk at 11 + 0 to 13 + 6 weeks of gestation. Assessment of the fetal nasal bone, ductus venosus flow and tricuspid flow were also routinely performed by appropriately trained sonographers. The performance of different screening policies was examined.
The study population consisted of 19 614 pregnancies with a normal karyotype or delivery of a phenotypically normal baby (euploid group) and 122 cases of trisomy 21. The best performance was achieved by a contingent policy in which first-stage screening was based on maternal age, fetal NT thickness and either tricuspid valve or ductus venosus blood flow, followed by biochemical testing only those with an intermediate risk, of 1 in 51 to 1 in 1000 (which constituted about 20% of the total). The performance of contingent screening in which first-stage testing relies on biochemistry was poorer than when first-stage screening was performed by ultrasound examination because, in order to achieve the same detection rate, the false-positive rate was twice as high.
Effective first-trimester screening for trisomy 21 can be achieved by a contingent policy in which first-stage testing is based on ultrasound examination and second-stage biochemical testing is carried out in only 20% of the patients.
本研究旨在检验在孕早期唐氏综合征筛查中， contingent 策略的表现。在这种策略中，首先通过结合母亲年龄、胎儿颈项透明层（NT）厚度、鼻骨是否存在、静脉导管或三尖瓣血流，来估计风险，仅对处于中等风险的孕妇进行生化检测。我们还研究了另一种策略的表现，该策略首先通过母亲年龄和生化检测的组合来估计风险，仅对处于中等风险的孕妇进行超声检查。
本研究的数据来源于在 11+0 至 13+6 孕周的一站式早孕期风险评估诊所，对单胎妊娠进行唐氏综合征的前瞻性筛查，标志物为母亲年龄、胎儿 NT 厚度和母血清游离 β-人绒毛膜促性腺激素（β-hCG）和妊娠相关血浆蛋白-A（PAPP-A）的组合。由经过适当培训的超声医生常规评估胎儿鼻骨、静脉导管血流和三尖瓣血流。研究了不同筛查策略的表现。
研究人群包括 19614 例正常核型或表型正常婴儿（整倍体组）和 122 例唐氏综合征。表现最好的是 contingent 策略，该策略的第一阶段筛查基于母亲年龄、胎儿 NT 厚度和三尖瓣或静脉导管血流，仅对处于中等风险的孕妇进行生化检测，风险为 1/51 至 1/1000（约占总数的 20%）。依赖于生化检测的 contingent 筛查的表现不如仅通过超声检查进行第一阶段筛查，因为为了达到相同的检出率，假阳性率要高出两倍。
通过 contingent 策略，可以有效地进行唐氏综合征的早孕期筛查，该策略的第一阶段基于超声检查，仅对 20%的孕妇进行生化检测。
