| Background and Objective China is a country with a high incidence of birth defect,and has maintained a birth defect rate of 5.6%.Approximate 900,000 infants with congenital defects are born per year.Chromosome anomalies are the main cause for birth defects,and there is no effective treatment at present.Prenatal screening and prenatal diagnosis are essential for the prevention of birth defects.As conventional serological prenatal screening is limited by its high false positive rate,and invasive prenatal diagnosis has a certain of surgery abortion risk,the compliance of women with high risk pregnancy is relatively low,which leads to the birth of birth defects.Along with the execution of the second-child policy,the portion of pregnant women over 35 years has significantly enlarged.According to Measures for the Implementation of the Law of the People’s Republic of China on Mother and Infant Health care and Management Measures of Prenatal Diagnosis Technology,pregnant women over 35 years are advised for invasive prenatal diagnosis,which being great pressure to prenatal diagnosis institutions.A new screening and diagnosing strategy with higher accuracy,higher safety and higher reliability are demand.So the purpose of this study is to explore the application value of noninvasive prenatal test(NIPT)in prenatal screening and prenatal diagnosis.Method From Feb.2015 to Dec.2017,321,788 pregnant women were provided with second trimester serological prenatal screening,and 38,862 cases of NIPT has been carried out for those who were defined as high risk,critical high risk,aged risk,etc.Trisomy 21,trisomy 18,trisomy 13 and other abnormal result of NIPT(such as sex chromosome anomalies or autosome CNVs)were counted.Amniocentesis karyotype analysis was provide to those with NIPT high risk of trisomy 21,trisomy 18 and trisomy 13 and chromosomal microarray analysis(CMA)was provided to those with NIPT suggestion of sex chromosome anomalies or autosome CNVs.Results(1)Among the 38,862 pregnant women who had accepted NIPT,538 cases of fetal aneuploidies and other chromosomal anomalies were screened out,reaching a total NIPT positive rate of 1.38%,including 245 cases of trisomy 21 high risk,46 cases of trisomy 18 high risk,9 cases of trisomy 13 high risk,149 cases of sex chromosome anomalies high risk and 89 cases of autosome CNVs risk.(2)In total 460 pregnant women which had voluntarily accepted amniocentesis,308 cases of chromosomal abnormal fetus were diagnosed,including 214 cases of trisomy 21,38 cases of trisomy 18,2 cases of trisomy 13,33 cases of sex chromosome anomalies and 21 cases of autosome anomalies(4 cases of balanced translocation and 17 cases of CNVs).Two NIPT high risk pregnant women who had refuse prenatal diagnosis for religion reason lately reported in the telephone follow-up that they both gave birth to a Down’s syndrome baby.By statistic,the positive predictive value of NIPT to trisomy 21,trisomy 18,trisomy 13,sex chromosome anomalies and autosome CNVs is 91.91%(216/235),82.61%(38/46),25%(2/8),35.87%(33/92)and 25.93%(21/81),respectively.(3)For cases with sex chromosome anomalies and autosome CNVs suggested by NIPT,CMA has higher diagnosis rate over chromosome karyotype analysis.(4)The high risk ratio of serological screening,the positive rate of NIPT and the portion of the diagnosed chromosome abnormal fetus of the pregnant women over 35 years are all significantly higher than that of the women under 35 years(P< 0.05).Conclusion(1)NIPT has both extreme accuracy towards the screening of trisomy 21 and outstanding screening accuracy for trisomy 18 and trisomy 13,making it a safe,effective and well-accepted method of prenatal screening that worth wide spreading,especially for pregnant women over 35 years.However,there are still notable false positive incidence,prevent it from completely replacing amniocentesis karyotype test.(2)NIPT has promising value in detection of sex chromosome anomalies and autosome CNVs.The prenatal diagnosis rate can be increased by combining CMA with chromosomal karyotype analysis. |
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