![]() Contingent screening has the potential to reduce invasive diagnostic test and to increase the detection rate of fetal Down syndrome, depending on the different traditional screening risk cut-offs 18, 19, 20. Recent studies show that a contingent strategy was more cost-effective, in which a high risk group is identified through traditional screening methods and only pregnancies in this group are offered NIPS screening 11, 12, 13, 14, 15, 16, 17. ![]() While NIPS as first-line screening has been suggested, but it was too expensive to be popularized in developing countries. A plenty of researches have indicated the excellent performance of NIPS in fetal Down syndrome screening 7, 8, 9, 10. In the past decade, NIPS based on massively parallel genomic sequencing (MPS) technology has been widely applied for the clinical detection of trisomy 21, trisomy 18, and trisomy 13 6. Different countries and regions adopt different screening strategies. The efficiency of screening tests are related to the screening strategies, which can vary with the number of biochemical makers, the timing of screening, cut-off value and positive detection rate that we set. Over time, the screening has evolved by using double screening, triple screening, quadruple screening, CFTS, integrated screening and sequential screening. When serum biochemical screening was introduced in the China, a hybrid approach was implemented in which amniocentesis was offered to all patients ≥35 years old and to patients <35 years old who were at increased risk based on the maternal serum markers available at that time. ![]() Providing high risk pregnancies prenatal diagnosis, the analysis of fetus chromosome collected via amniocentesis or chorionic villus sampling 4, 5. It is mainly to find pregnancies considered to be at high risk as determined by prenatal aneuploidy screening. At present, there is no effective treatment for Down syndrome, which can effectively reduce the birth rate of Down syndrome. Down syndrome usually has multiple system complications 3, causing serious mental and economic burden to the family and society. ![]() DS patients have characteristic facial features, such as wide eye distance, low bridge of nose, eyelid cleft and so on, which are often manifested as moderate to severe inherited intellectual disability and abnormal growth and development 2. According to local health and economic conditions, adopting appropriate traditional screening with suitable cut-offs as first-line screening will contributed to a cost-effective screening model.ĭown syndrome (DS), also known as trisomy 21 syndrome, is the most common chromosomal abnormality, with incidence of 1 in 1000 to 1 in 700 live births 1, 2. Our study demonstrated if only one traditional screening was allowed to screen pregnant women, CFTS was recommended as the first choice. Other screening tests as the first-line screening with intermediate risk of 1:51~1:1000 had the lowest cost, there DR were 90.91%, 84.62%, 91.67%, respectively. When intermediate risk was 1:51 ~1:1500, CFTS as first-line screening had the lowest cost with DR of 93.94%. Compared with other screening tests, combined first-trimester screening (CFTS) had the lowest proportion of high risk (≥1:270) with the highest detection rate (DR) (78.79%) and the lowest proportion of intermediate risk (1:271~1:1000). We analyzed cost and performance of various screening models with contingent screening of different risk cut-offs. The 9 contingent models were combined by high risk cut-offs of 1:50, 1:100, 1:270 and intermediate risk cut-offs of 1:1000, 1:1500, 1:2000. Pregnant women underwent one of four traditional screening tests. To discuss combinations of traditional screening and noninvasive prenatal screening (NIPS) and to compare which traditional screening is the most suitable first-line screening approach to NIPS, pregnant women were recruited in this retrospective observational study.
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