A New Strategy On Down Syndrome Screening Of Advanced Maternal Age

Down syndrome (DS), also known as Trisomy 21, is a common chromosomal disorder which seriously affecting the fetus mental and physical development. The incidence is considered to be 1/600-1/800 in our country, which accounts for most of the proportion of chromosomal diseases in birth defects. Nowadays, maternal serum, genetics ultrasound and amniocentesis have been widely used in prenatal screening and diagnosis. The first two methods are noninvasive, which are easy to be accepted by the pregnant women and their families. Amniocentesis is the gold standard for the diagnosis of DS, however,0.5%-1% fetal loss rate make many families hesitate to choose it. Integrating the existing means to improve the accuracy of screening for DS, meanwhile to reduce the rate of misdiagnosis and find a new better method for the chromosome disease diagnosis are becoming the direction in fetal medicine practitioners.Advanced maternal age (AMA) is becoming a huge and high-profile population with the socio-economic development and progress. In order to improve the quality of births, reduce the number of children with DS, at present, our country is generally recommended the AMA to directly carry out the amniocentesis and fetal chromosome examinations in proper gestational weeks. Most AMA want to avoid amniocentesis because of very hoping to have a child, or because of infertility treatment for many years, or because of IVF pregnancy or other reasons. In recent years, international society call on amendments of strategy of DS in AMA, amniocentesis directly is not the only choice for them. Therefore we hope to set up a prenatal screening model and scoring system for DS of AMA to improve screening accuracy while greatly reduce the chance of amniocentesis.In recent years, the use of the fetal cells or genetic materials in maternal blood for the diagnosis of DS has made some progresses. Professor Lo, from Chinese University of Hong Kong, first reported the presence of fetal DNA in maternal blood in 1997, and using RNA molecules expressed by a gene on chromosome 21 in subsequent studies, precisely calculated the proportion of the fetal RNA molecules by the father and mothers inheriting by Mass-Array technology to diagnose DS. The content of fetal DNA in maternal peripheral blood is between 5%-30%, the greater the gestational weeks, the higher the content of fetal DNA in the peripheral blood. Another change is the relative content of fetal free DNA of chromosome 21 from Down's in maternal plasma, and subtle changes of this content may be detected accurately by the high-throughput sequencing technology. Currently more mature method is the second-generation non-invasive high-throughput DNA sequencing technology, which has not been widely applied in our country.Our study will establish a noninvasive scoring system for DS, meanwhile exploring the value of non-invasive DNA testing technology for DS screening in AMA.Our subject contains two parts:First, the establishment of a noninvasive screening model and scoring system for DS. Second, the detection of the value of second-generation non-invasive high-throughput DNA sequencing technology in screening of DS of AMA.Part I:the establishment of a non-invasive screening model and scoring system for DSObjective:To establish a prenatal screening model and scoring system for DS of AMA. Aim at improving screening accuracy while greatly reducing the chance of amniocentesis by the use of this screening model and scoring system in AMA.Methods:A retrospective analysis of a total of 1192 cases of AMA (?35 years of age at delivery) from January 2009 to January 2014 in Obstetrics and Gynecology Hospital of Fudan University, including six cases of DS. The maternal age, the adverse pregnancy history, the history of drugs exposure in early pregnancy, the first trimester DS screening results including PAPP-A and ?-HCG testing and NT, second trimester DS triple serological screening results and second-trimester genetic sonography results were recorded. All screening informations and pregnancy outcomes were registered in accordance with the standard of our hospital. According to the statistical analysis of 1192 cases of AMA, the factors that affect Down's positive result of AMA were selected by univariate and multivariate logistic regression analysis and noninvasive prenatal screening model and scoring system for DS was created. Receiver operating characteristics curve (ROC curve)and the area under ROC curve(AUC)were used to show the accuracy of the self-built model for predicting the risk of DS.Results:1.Comparison between DS negative group and positive group, maternal age, history of exposure to drugs during the first trimester, fetal ventriculomegaly, thickened nuchal fold, shortened femur, shortened humerus and heart malformations have obvious correlation with DS positive result and there are statistics difference(p<0.05); 2.By univariate and multivariate logistic regression analysis on 1192 cases of AMA, we have filtered out seven meaningful indicators for Down prediction:maternal age, exposure history of drugs and other adverse factors during the first trimester, fetal ventriculomegaly, thickened nuchal fold, shortened femur, shortened humerus, heart malformations; 3.The self-built model: Logit(P)=-24.595+0.474×age+3.045×exposure history of drugs and other adverse factors during the first trimester+2.864×fetal ventriculomegaly+1.081×thickened nuchal fold+2.823×shortened femur-0.602× shortened humerus+3.654×heart malformations.4.The AUC of self-built model for predicting the risk of DS in AMA is over 0.8, indicating that self-built model have good predictive value for the risk of DS in AMA.Conclusion:The self-built model can better predict the risk of DS in AMA.Part ?:the detection of the value of second-generation non-invasive high-throughput DNA sequencing technology in screening of DS of AMAObjective:To disclose the value of non-invasive DNA testing technology for the screening of DS in AMA. And to provide an important complement method for prenatal screening of DSMethods:With Double-blind trial design,8ml of disposable peripheral venous blood after 12 weeks of pregnancy were collected and sent to Beijing BerryGenomics Co.,Ltd. for high-throughput testing by 12-plex Hiseq2000 platform. All cases were recorded with unique cards or detailed clinical data and followed over time to delivery. Those who underwent amniocentesis chromosome examination would consider the amniotic fluid fetal karyotyping as the gold standard for diagnosis of DS; while without it the birth outcomes (neonatology doctor's inspection result) would be the replacement. Then according to the statistics of 87 cases of AMA, we calculated the sensitivity, specificity and other indicators of non-invasive DNA testing technology in the data.Results:87 cases of AMA were collected. Five cases of the number of chromosomal abnormalities (three cases of trisomy 21, one case of trisomy 18, one case of 47, XXX) were accurately diagnosed.Conclusion:Our study supports that non-invasive DNA testing is a useful method of AMA screening of DS with the accuracy and specificity both 100%, and it may be an important complement screening methods for DS in AMA.