Meta-analysis Of Non-invasive Prenatal Test And Research Of Prenatal Diagnosis Based On Cervical Trophoblast In The First Trimester

Research backgroundChromosomal aberrations are the most common cases of birth defects and mainly include the number and structure abnormalities of autosome or sex chromosome,such as Down’s syndrome(trisomy21 or T21),Edwards syndrome(trisomy 18 or T18)and Patau syndrome(trisomy 13 or T13).They may negatively affect fetus and cause organ abnormalities or even death in utero.Traditional non-invasive methods for detecting abnormal chromosomes such as ultrasound and prenatal serum screening may cause high proportion of false negatives and false positives.Whereas,invasive testing methods for accurate diagnosis such as chorionic villus sampling(CVS),amniocentesis(AC)and cordocentesis may lead to miscarriage and infection.The discovery of fetal DNA in the cell-free plasma of pregnant women and the development of next-generation sequencing(NGS)based methods enabled more accurate screening of fetal chromosomal abnormalities by non-invasive prenatal testing(NIPT).However,studies have found that an early gestation or a high maternal BMI may lead to an unsatisfactory cell free DNA(cfDNA)fetal fraction.Therefore,we systematically measure test accuracy of NIPT for Down,Edwards and Patau syndromes using cell-free fetal DNA and identify factors affecting accuracy.We aim to retrieve the trophoblast cells from the cervix canal to explore a new sampling method for NIPT.Instead of using separation before identification,we extract DNA directly and then perform the sequencing procedure.To a great extent,this avoids the possible loss of target cells.The successful isolation of trophoblast cells from the cervix canal early during gestation will enable an earlier application of NIPT to detect chromosomal abnormalities and will provide a new appropriate method and theoretical basis for the prospective prevention of birth defects.Research purposes1.To measure test accuracy of non-invasive prenatal testing(NIPT)based on cell-free fetal DNA for Down,Edwards and Patau syndromes and identify factors affecting accuracy.To compare the differences of the test accuracy among different risk populations and screening models.2.To retrieve the trophoblast cells from the maternal cervix to develop a new non-invasive sampling method which can directly obtain and analyze fetal genetic information without separation and enrichment.3.To explore a new method for identifying the fetal origin of cervical trophoblasts and aim to advance the non-invasive detection window earlier to 10 weeks gestation in order to detect birth defects such as chromosomal diseases,genomic diseases and monogenic diseases earlier.Research methods1.We searched multiple Chinese and English databases,analyzed the accuracy of non-invasive prenatal testing based on cell-free fetal nucleic acid of maternal blood,and explored its influencing factors through bivariate meta-analysis and subgroup analysis.2.We enrolled pregnant woman in the first trimester who wanted to undergo induced abortion at Beijing Hospital.Peripheral blood,cervix specimen,and the abortion tissue were collected and processed for each patient.The Sex Determining Region Y(SRY)gene was tested.3.We enrolled pregnant woman in the first trimester who wanted to undergo induced abortion at Beijing Hospital.Peripheral blood,cervix specimen,and the abortion tissue were collected and processed for each patient.Allele frequencies of the mutated gene loci of the maternal blood and the cervix sample were compared.Research results1.60,51 and 42 studies retrieved were included in the review for Down,Edwards and Patau syndromes.Quality appraisal identified high risk of bias in included studies,funnel plots showed evidence of publication bias.Pooled sensitivity was 98.6%(98.1%-99.0%)for Down,97.9%(96.7%-98.7%)for Edwards,and 93.0%(88.9%-95.9%)for Patau syndrome.Pooled specificities were all 99.9%(99.9%-100.0%).Sensitivity was lower in twin than singleton pregnancies and also lower in the first trimester of pregnancy.2.The allele frequencies of the mutated gene loci showed no significant difference between the maternal blood and the cervix sample.But we successfully detected signal of the SRY genes in the cervix sample of the patients carrying a male fetus without separation and identification.Conclusion:Non-invasive prenatal testing based on cell-free fetal DNA is very sensitive and specific for autosomal trisomies,but it cannot be applied to all subgroups and is not yet a substitute for current invasive prenatal diagnostic tests.The detection of the SRY gene in a cervix sample indicated a successful retrieval of trophoblast cells from the cervix canal.Further study needs to be conducted to verify our finding before its application to the clinical settings.