Study Of Second-trimester Screening For Down Syndrome In Dried Blood Spots

ObjectiveTo obtain the stable and optimal assays of AFP, Freeβ-hCG and uE3 in dried blood spots (DBS) as screening methods for detecting Down syndrome (DS) in the second-trimester.To determin screening positive cut-off of screening for DS in DBS and explore DBS screening efficiency.To investigate the consistency between dried blood spots and fresh serum screening for DS in the second trimester pregnancy.Materials and MethodsThe serum samples and DBS of 3362 gravidas were collected from the obstetric clinics of Haidian Women and Children hospital, from December,2009 to September, 2010. Clinical information was collected simultaneously. A self-matching design for DBS and serum sampls, we measured all AFP, freeβ-HCG and uE3 concentrations of serum and DBS samples. Coherence study of second-trimester screening for DS in dried blood spots and sera. The detection rates of DBS and serum prenatal screening program were compared, and their correlation was evaluated.Results1. The sensitivitise of AFP, free-β-HCG and uE3 in DBS were 0.26u/ml,0.54ng/ml,0.29nmol/1.2. Multiples of medians (MoM) of freeβ-HCG and uE3 distribution in DBS were described as unimodal curves with their medians and modes close to 1. The AFP MoM median of DBS was higher than that of serum.3. Follow-up rate was 90.81%.91 gravidas accepted amniocentesis. Four abnormal choromosome karyotypes were diagnosed as 2 fetals with DS (incidence rate 0.65%o), 1 fetal with 45,X,1 fetal with 13-trisome.There were 1 fetal with NTD and 44 other malformations among these 3053 gravidas.4. The values at risk of DBS double test (AFP+free-βHCG) and DBS triple test (AFP +free-βHCG+uE3) were calculated by LifeCycle (LC) software respectively. When DS screening positive cut-off was 1/220, the false positive rate (FPR) of them were 2.85%,5.08%, the specificity of them were 97.15%,94.92%. When DS screening positive cut-off was 1/270, the FPR of them were 3.83%,6.22%, the specificity of them were 96.23%,93.83%.5. When DS screening positive cut-off was 1/270, the DS detective rate of DBS double test, DBS triple test and serum triple test was 100%, the FPR and specificity of serum triple test were 6.98% and 93.08%..6. When ONTD screening positive cut-off was AFP>2.5MoM, the FPR of serum screening and DBS screening were 0.7%,8.8%. When AFP≥3.0MoM, the FPR of DBS screening was3.9%. When 18-trisom screening positive cut-off was 1/350, the FPR of serum screening, DBS double test and DBS triple test were 0.21%,0.33% and 3%.7. The performance of DBS screening program was consistent with that of the serum screening program.8. The consistency between DBS and serum screening for DS among advanced maternal age (AMA) was perfect, the FPR of DBS test and serum test for AMA were 12.12%, 15.16%. The prenatal diagnose FPRof DBS double test, DBS triple test and serum screening for high risk gravidas were 9.52%,5.88% and 2.38%.Conclusions1.. The performance of DBS screening program was consistent with that of the conventional serum screening program.2. The DBS double test and DBS triple test were feasible. The DBS screening for DS in the second-trimester positive cut-off was 1/220.3. The coherence between them was perfect. However, the coherence between DBS screening and serum screening was unsatisfied. The DBS double test was more effective than DBS triple test. The DBS test was more efficient than serum screening for DS.4. The performance of DBS screening for DS high risk gravidas was not only more effective in Prenatal diagnose but also more cost-effective than serum screening in this study.