无创产前检测对于胎儿染色体拷贝数变异的检测价值

目的探讨无创产前检测(non-invasive prenatal testing,NIPT)对于胎儿染色体拷贝数变异(copy number variations,CNVs)的检测价值。方法收集18661例接受NIPT检测的孕妇的临床资料,为提示胎儿携带CNVs的孕妇提供羊水染色体核型或/及染色体微阵列分析,并分析结果的一致性。结果在全部样本中,NIPT共提示21三体58例、18三体18例、13三体19例、18/21三体1例。88例孕妇接受了介入性产前诊断,59例的染色体微阵列分析结果与NIPT一致,符合率为67.05%。NIPT还检出CNVs 37例,其中19例(微缺失15例、微重复4例)接受了介入性产前诊断,14例的验证结果与NIPT一致,符合率为73.68%。结论NIPT检测具有较高的灵敏度和准确性,对检测提示的CNVs应考虑进行介入性产前诊断,追溯其亲代起源,为临床提供指导。     

Chromosome microarray analysis should be offered to all invasive prenatal diagnostic testing following a normal rapid aneuploidy test result

Chromosomal microarray analysis (CMA) has now replaced karyotyping in the analysis of prenatal cases with a fetal structural anomaly, whereas in those pregnancies undergoing invasive prenatal diagnosis with a normal fetal ultrasound, conventional karyotyping is still performed. The aims of this study were to establish the diagnostic yield of CMA in prenatal diagnosis, and to provide new data that might contribute to reconsider current practices. We reviewed 2905 prenatal samples with a normal rapid aneuploidy detection test referred for evaluation by CMA testing. Our study revealed pathogenic and reported susceptibility copy number variants associated with syndromic disorders in 4.8% (n = 138/2905) of cases, being 2.8% (n = 81/2905) the estimated added diagnostic value of CMA over karyotyping. Clinically significant CMA abnormality was detected in 5.4% (107/1975) of the fetuses with ultrasound anomalies and in 1.4% (5/345) of those considered as low-risk pregnancies. Our series shows that in prenatal samples, CMA increases 2-fold the diagnostic yield achieved by conventional karyotyping.     

Chromosomal microarray analysis as a first-line test in pregnancies with a priori low risk for the detection of submicroscopic chromosomal abnormalities

In this study, we aimed to explore the utility of chromosomal microarray analysis (CMA) in groups of pregnancies with a priori low risk for detection of submicroscopic chromosome abnormalities, usually not considered an indication for testing, in order to assess whether CMA improves the detection rate of prenatal chromosomal aberrations. A total of 3000 prenatal samples were processed in parallel using both whole-genome CMA and conventional karyotyping. The indications for prenatal testing included: advanced maternal age, maternal serum screening test abnormality, abnormal ultrasound findings, known abnormal fetal karyotype, parental anxiety, family history of a genetic condition and cell culture failure. The use of CMA resulted in an increased detection rate regardless of the indication for analysis. This was evident in high risk groups (abnormal ultrasound findings and abnormal fetal karyotype), in which the percentage of detection was 5.8% (7/120), and also in low risk groups, such as advanced maternal age (6/1118, 0.5%), and parental anxiety (11/1674, 0.7%). A total of 24 (0.8%) fetal conditions would have remained undiagnosed if only a standard karyotype had been performed. Importantly, 17 (0.6%) of such findings would have otherwise been overlooked if CMA was offered only to high risk pregnancies.The results of this study suggest that more widespread CMA testing of fetuses would result in a higher detection of clinically relevant chromosome abnormalities, even in low risk pregnancies. Our findings provide substantial evidence for the introduction of CMA as a first-line diagnostic test for all pregnant women undergoing invasive prenatal testing, regardless of risk factors.     

Intrauterine phenotype features of fetuses with Williams–Beuren syndrome and literature review

Williams–Beuren syndrome (WBS) is a well-defined multisystem chromosomal disorder that is caused by a chromosome 7q11.23 region heterozygous deletion. We explored prenatal diagnosis of WBS by ultrasound as well as multiple genetic methods to characterize the structural variants of WBS prenatally. Expanded noninvasive prenatal testing (NIPT-plus) was elected as a regular prenatal advanced screen for risk assessments of fetal chromosomal aneuploidy and genome-wide microdeletion/microduplication syndromes at the first trimester. At the second and three trimester, seven prenatal cases of WBS were evaluated for the indication of the invasive testing, the ultrasound features, cytogenetic, single-nucleotide polymorphism array (SNP array), and fluorescent quantitative PCR (QF-PCR) results. The NIPT-plus results for seven fetuses were low risk. All cryptic aberrations were detected by the SNP array as karyotyping analyses were negative. Subsequently, QF-PCR further confirmed the seven deletions. Combining our cases with 10 prenatal cases from the literature, the most common sonographic features were intrauterine growth retardation (82.35%, 14/17) and congenital cardiovascular abnormalities (58.82%, 10/17). The manifestations of cardiovascular defects mainly involve supravalvar aortic stenosis (40%, 4/10), ventricular septal defect (30%, 3/10), aortic coarctation (20%, 2/10), and peripheral pulmonary artery stenosis (20%, 2/10). To the best of our knowledge, this is the first largest prenatal study of WBS cases with detailed molecular analysis. Aortic coarctation combined with persistent left superior vena cava and right aortic arch cardiovascular defects were first reported in prenatal WBS cases by our study.     

2473例双胎妊娠的无创产前检测结果分析

目的分析探讨无创产前检测(non-invasive prenatal testing,NIPT)对于双胎妊娠胎儿非整倍体的检测价值。方法选取2016年1月至2019年12月在本中心接受NIPT检测的2473例双胎孕妇,利用高通量测序和生物信息学分析测算胎儿染色体非整倍体的风险率,为高风险孕妇提供羊膜腔或绒毛穿刺,并对结果进行随访。结果在2473例孕妇中,共检出31例(1.25%)胎儿染色体高风险,其中5例为21-三体,1例为21号染色体缺失,4例为18-三体,7例为性染色体异常,14例为微缺失/微重复。经产前诊断或新生儿外周血染色体核型分析,共确诊5例21-三体、3例18-三体,1例性染色体异常,2例微缺失/微重复,其阳性预测值分别为100%、75%、25%和25%。结论NIPT筛查双胎妊娠胎儿染色体非整倍体的准确性较高,是一种安全有效的筛查手段,对21-三体的筛查效率高于其他染色体。     

限制性胎盘嵌合对无创产前检测的影响及临床分析

目的探讨限制性胎盘嵌合(confined placental mosaicism,CPM)对无创产前检测(non-invasive prenatal testing,NIPT)以及妊娠结局的影响。方法应用低深度全基因组测序(copy number variation sequencing,CNV-seq)和单核苷酸多态性微阵列技术(single nucleotide polymorphism array,SNP-array)对8例NIPT假阳性病例进行胎盘多个位置的遗传学检测,结合临床资料分析CPM对NIPT以及妊娠结局的影响。结果在8例NIPT假阳性病例中,5例为CPM,分别为9号三体、13三体、21三体、22三体以及X三体CPM;胎盘不同区域的染色体异常比例差异明显(4%~80%)。5例CPM中,2例表现为胎儿生长受限(fetal growth restriction,FGR)合并其他超声异常,1例表现为孤立性FGR,其余2例生长发育正常。结论CPM是NIPT假阳性的重要原因,NIPT对CPM有较高的敏感性;CPM可能与FGR相关。重视CPM对于NIPT检测前后的遗传咨询以及妊娠管理有重要帮助。     

0.5 Mb Array as a First‐Line Prenatal Cytogenetic Test in Cases without Ultrasound Abnormalities and Its Implementation in Clinical Practice

Using whole‐genome array testing instead of karyotyping in prenatal diagnosis for all indications may be desirable because of the higher diagnostic yield and shorter reporting time. The goal of this research was finding the optimal array resolution that could replace routine prenatal karyotyping in cases without ultrasound abnormalities, for example, referred for advanced maternal age or abnormal first trimester screening. As variants of unknown clinical significance (VOUS), if reported, might complicate decision‐making about continuation of pregnancy, such an optimal array resolution should have a high abnormality detection rate and reveal a minimal amount of VOUS. The array data of 465 fetuses were retrospectively evaluated with several resolution levels, and the Decipher microdeletion/microduplication syndrome list was reviewed to assess what could be theoretically missed with a lower resolution. A 0.5‐Mb resolution showed a high diagnostic yield potential and significantly minimized the number of VOUS. Based on our experience, we recommend genomic SNP array as a first‐tier test in prenatal diagnosis. The resolution should be chosen based on the indication. In cases of fetal ultrasound abnormalities or intrauterine fetal death (IUFD), high‐resolution analysis should be done. In other cases, we advise replacing karyotyping by SNP array analysis with 0.5 Mb resolution.     

Benefits and Burdens of Using a SNP Array in Pregnancies at Increased Risk for the Common Aneuploidies

We present the nature of pathogenic SNP array findings in pregnancies without ultrasound (US) abnormalities and show the additional diagnostic value of SNP array as compared with rapid aneuploidy detection and karyotyping. 1,330 prenatal samples were investigated with a 0.5‐Mb SNP array after the exclusion of the most common aneuploidies. In 2.7% (36/1,330) of the cases, pathogenic chromosome aberrations were found; a microscopically detectable abnormality in 0.7% and a submicroscopic aberration in 2%. Our results show that in addition to the age‐ or screening‐related aneuploidy risk, in pregnancies without US abnormalities, there is a risk of 1:148 (9/1,330) for a (sub)microscopic abnormality associated with an early‐onset often severe disease, 1:222 (6/1,330) for a submicroscopic aberration causing an early‐onset disease, 1:74 (18/1,330) for carrying a susceptibility locus for a neurodevelopmental disorder, and 1:443 (3/1,330) for a late‐onset disorder (hereditary neuropathy with liability to pressure palsies in all three cases). These risk figures are important for adequate pretest counseling so that prospective parents can make informed individualized choices between targeted prenatal testing and broad testing with SNP array. Based on our results, we believe if invasive testing is performed, SNP array should be the preferred cytogenetic technique irrespective of the indication.     

Experience of chromosomal microarray applied in prenatal and postnatal settings in Hong Kong

Chromosomal microarray (CMA) is recommended as a first tier investigation for patients with developmental delay (DD), intellectual disability (ID), autistic spectrum disorder (ASD), and multiple congenital anomalies (MCA). It is widely used in the prenatal and postnatal settings for detection of chromosomal aberrations. This is a retrospective review of all array comparative genomic hybridization (aCGH/ array CGH) findings ascertained in two major prenatal and postnatal genetic diagnostic centers in Hong Kong from June 2012 to December 2017. Medical records were reviewed for cases with pathogenic and variants of uncertain clinical significance (VUS). Classification of copy number variants (CNVs) was based on current knowledge and experience by August 2018. The aims of this review are to study the diagnostic yield of array CGH application in prenatal and postnatal settings in Hong Kong and to describe the spectrum of abnormalities found. Prenatal indications included abnormal ultrasound findings, positive Down syndrome screening, abnormal noninvasive prenatal test results, advanced maternal age and family history of chromosomal or genetic abnormalities. Postnatal indications included unexplained DD, ID, ASD, and MCA. A total of 1,261 prenatal subjects and 3,096 postnatal patients were reviewed. The prenatal diagnostic yield of pathogenic CNV and VUS (excluding those detectable by karyotype) was 3.5%. The postnatal diagnostic yield of pathogenic CNV was 15.2%. The detection rates for well‐defined microdeletion and microduplication syndromes were 4.6% in prenatal and 6.1% (1 in 16 index patients) in postnatal cases, respectively. Chromosomes 15, 16, and 22 accounted for over 21 and 25% of pathogenic CNVs detected in prenatal and postnatal cohorts, respectively. This review provides the first large scale overview of genomic imbalance of mostly Chinese patients in prenatal and postnatal settings.     

Singleton exome sequencing of 90 fetuses with ultrasound anomalies revealing novel disease-causing variants and genotype–phenotype correlations

Exome sequencing has been increasingly implemented in prenatal genetic testing for fetuses with morphological abnormalities but normal rapid aneuploidy detection and microarray analysis. We present a retrospective study of 90 fetuses with different abnormal ultrasound findings, in which we employed the singleton exome sequencing (sES; 75 fetuses) or to a lesser extent (15 fetuses) a multigene panel analysis of 6713 genes as a primary tool for the detection of monogenic diseases. The detection rate of pathogenic or likely pathogenic variants in this study was 34.4%. The highest diagnostic rate of 56% was in fetuses with multiple anomalies, followed by cases with skeletal or renal abnormalities (diagnostic rate of 50%, respectively). We report 20 novel disease-causing variants in different known disease-associated genes and new genotype–phenotype associations for the genes KMT2D, MN1, CDK10, and EXOC3L2. Based on our data, we postulate that sES of fetal index cases with a concurrent sampling of parental probes for targeted testing of the origin of detected fetal variants could be a suitable tool to obtain reliable and rapid prenatal results, particularly in situations where a trio analysis is not possible.Subject terms: Genetics research, Disease genetics     

Clinical implementation of NIPT – technical and biological challenges

Non‐invasive prenatal testing (NIPT) for fetal aneuploidy detection is increasingly being offered in the clinical setting. Whereas the majority of tests only report fetal trisomies 21, 18 and 13, genome‐wide analyses have the potential to detect other fetal, as well as maternal, aneuploidies. In this review, we discuss the technical and clinical advantages and challenges associated with genome‐wide cell‐free fetal DNA profiling.     

无创产前筛查技术在产前筛查与诊断技术体系中的效能分析

目的评价无创产前检测(non-invasive prenatal testing,NIPT)技术在产前筛查中的效能及其在产前诊断体系中的作用。方法对22649例单胎孕妇的产前筛查结果及诊断路径进行效能分析。对同期接受介入性产前诊断的9268例本院和转诊孕妇的指征及结局进行效能分析。结果孕妇选择唐筛比例为60.24%,年龄主要为35岁以下;选择NIPT者比例为34.74%,年龄主要为35~39岁。NIPT对于胎儿21、18、13三体高风险的总体检出率为0.89%,阳性预测值为75.71%,其中唐筛临界风险孕妇的NIPT高风险检出率为0.30%。高龄孕妇和唐筛高风险孕妇人数占产前诊断孕妇63.04%和21.22%,阳性预测值为5.1%和5.13%。NIPT高风险孕妇人数占产前诊断孕妇的2.30%,阳性预测值为54.46%。结论随着中国孕妇年龄结构的改变和妊娠复杂性的增加,以NIPT为主的筛查模式将有助于提升现有产前筛查和诊断技术体系的效能。     

Microarray comparative genomic hybridization (CGH)-based prenatal diagnosis for chromosome abnormalities using cell-free fetal DNA in amniotic fluid

Cell-free fetal DNA (cffDNA) in the supernatant of amniotic fluid, which is usually discarded, can be used as a sample for prenatal diagnosis. For rapid prenatal diagnosis of frequent chromosome abnormalities, for example trisomies 13, 18, and 21, and monosomy X, using cffDNA, we have developed a targeted microarray-based comparative genomic hybridization (CGH) panel on which BAC clones from chromosomes 13, 18, 21, X, and Y were spotted. Microarray-CGH analysis was performed for a total of 13 fetuses with congenital anomalies using cffDNA from their uncultured amniotic fluid. Microarray CGH with cffDNA led to successful molecular karyotyping for 12 of 13 fetuses within 5 days. Karyotypes of the 12 fetuses (one case of trisomy 13, two of trisomy 18, two of trisomy 21, one of monosomy X, and six of normal karyotype) were later confirmed by conventional chromosome analysis using cultured amniocytes. The one fetus whose molecular-karyotype was indicated as normal by microarray CGH actually had a balanced translocation, 45,XY,der(14;21)(q10;q10). The results indicated that microarray CGH with cffDNA is a useful rapid prenatal diagnostic method at late gestation for chromosome abnormalities with copy-number changes, especially when combined with conventional karyotyping of cultured amniocytes.     

Trisomy 18: Fetal ultrasound findings at different gestational ages

The aim of this article is evaluate the sonograhic findings in fetuses with trisomy 18 at different gestational ages. The cases were recruited from pregnant women, who underwent to prenatal diagnosis in the period from October 1995 to September 2006. Seventy-one fetuses with trisomy 18 were diagnosed. On review of the sonograms the majority of these cases had ultrasound anomalies (sensitivity of 91.5%). The most frequent anomalies were abnormalities of extremities (40.8%) and fetal growth restriction (35.2%). More frequently (54.9%) two or more anomalies were present. Nearly all fetuses with trisomy 18 had sonographic abnormalities. Likely improved high-resolution equipment and attention to details by skilled operators led to the detection of most anomalies to trisomy 18. Knowledge of types of specific ultrasound findings can improve prenatal diagnosis in order to provide invasive procedures only when indicated, and to avoid amniocentesis when ultrasound signs are not observed in women at high risk from positive biochemical testing.     

Expanding non‐invasive prenatal testing beyond chromosomes 21, 18, 13, X and Y

Non‐invasive prenatal testing (NIPT) based on cell‐free DNA in maternal plasma is being expanded to include additional chromosome abnormalities beyond those involving chromosomes 21, 18, 13, X and Y. Review of population cytogenetic data provides insight into the likely number of additional abnormalities detectable. Additional clinically significant and cytogenetically recognizable abnormalities are present in less than 0.1% of newborns but clinically significant, or potentially significant, sub‐microscopic imbalances are expected to be present in 1.7%. Cytogenetic studies on chorionic villus samples suggests that after excluding abnormalities involving chromosomes 21, 18, 13, X and Y, approximately 0.6% of NIPT results may be positive for an unbalanced abnormality attributable to mosaicism but most of these will not be confirmed at amniocentesis or in newborns. NIPT has also been developed for specific microdeletion syndromes and initial experience is now available. Laboratory procedures such as deeper sequencing and additional data analytics are rapidly evolving but even with existing protocols, it is already clear that NIPT does not necessarily need to be limited to trisomies 21, 18, 13 and the sex‐chromosome abnormalities. Patient educational materials and genetic counseling services need to be available for women offered expanded NIPT.     

Implementation of high‐resolution SNP arrays in the investigation of fetuses with ultrasound malformations: 5 years of clinical experience

Chromosome microarray analysis (CMA) has proven to be a powerful tool in postnatal patients with intellectual disabilities, and it is increasingly used in prenatal diagnosis. However, its diagnostic capabilities in prenatal diagnosis vary, and clinical experiences have failed to establish a consensus regarding CMA indications, the design and resolution of microarrays, and the notification and interpretation of copy number variations (CNVs). We present our 5 years of clinical experience using whole‐genome high‐resolution single nucleotide polymorphism (SNP) arrays to investigate 446 fetuses that had structural malformations detected with ultrasound but for which standard karyotyping analysis showed normal karyotypes. CMA revealed genomic CNVs in 323 (72.4%) cases and clinically significant CNVs in 11.4% of the fetuses (51/446), including 2 cases of uniparental disomy (UPD) as well as 1 case of cryptic mosaic monosomy of chromosome X. Variants of unknown significance (VOUS) existed in 2.0% of the tested fetuses (9/446). Our results demonstrate the value of whole‐genome high‐resolution SNP arrays in fetuses with congenital malformations and give a higher detection rate of clinically significant genomic imbalance, especially for detecting UPD. Sufficient communication between technicians and genetic counselors, along with parental testing and comparison with data from in‐house or international sources, can significantly reduce VOUS.     

Prenatal exome sequencing in fetuses with congenital heart defects

The genetic diagnosis of congenital heart defects (CHDs) is challenging because of genetic and phenotypic heterogeneity. The aim of our study was to evaluate the clinical value of whole exome sequencing (WES) in the prenatal diagnosis of CHDs in a large cohort. Trio-based WES was performed in 260 fetuses with CHDs negative for karyotype and chromosome microarray analysis results. WES produced a diagnostic yield of 10% (26/260) in the entire cohort. Relative high diagnostic rate was observed in cases with cardiac rhabdomyoma (60%), complex CHDs (16.7%), septal defect (14.0%), and conotruncal defect (9.9%). There was no significant difference between the diagnostic yields in simple and complex CHDs groups (9.9% vs 16.7%), and in non-isolated and isolated CHDs groups (15.7% vs 7.9%). The diagnostic yields in cases with CHDs with soft markers, CHDs with fetal growth restriction, and CHDs with other structural anomalies (syndromic CHDs) were 0 (0/13), 50% (1/2) and 18.2% (10/55), respectively. Variants of unknown significance were detected in 16 (6.2%) fetuses, and secondary findings in 7 (2.7%) cases. Variants in 14 candidate genes were identified. Our study demonstrates an incremental diagnostic yield by trio-based WES in the prenatal diagnosis of CHDs after routine tests, not as high as expected.     

Clinical Practice Guidelines for Prenatal Aneuploidy Screening and Diagnostic Testing from Korean Society of Maternal-Fetal Medicine: (2) Invasive Diagnostic Testing for Fetal Chromosomal Abnormalities

The Korean Society of Maternal Fetal Medicine proposed the first Korean guideline on prenatal aneuploidy screening and diagnostic testing, in April 2019. The clinical practice guideline (CPG) was developed for Korean women using an adaptation process based on good-quality practice guidelines, previously developed in other countries, on prenatal screening and invasive diagnostic testing for fetal chromosome abnormalities. We reviewed current guidelines and developed a Korean CPG on invasive diagnostic testing for fetal chromosome abnormalities according to the adaptation process. Recommendations for selected 11 key questions are: 1) Considering the increased risk of fetal loss in invasive prenatal diagnostic testing for fetal genetic disorders, it is not recommended for all pregnant women aged over 35 years. 2) Because early amniocentesis performed before 14 weeks of pregnancy increases the risk of fetal loss and malformation, chorionic villus sampling (CVS) is recommended for pregnant women who will undergo invasive prenatal diagnostic testing for fetal genetic disorders in the first trimester of pregnancy. However, CVS before 9 weeks of pregnancy also increases the risk of fetal loss and deformity. Thus, CVS is recommended after 9 weeks of pregnancy. 3) Amniocentesis is recommended to distinguish true fetal mosaicism from confined placental mosaicism. 4) Anti-immunoglobulin should be administered within 72 hours after the invasive diagnostic testing. 5) Since there is a high risk of vertical transmission, an invasive prenatal diagnostic testing is recommended according to the clinician''s discretion with consideration of the condition of the pregnant woman. 6) The use of antibiotics is not recommended before or after an invasive diagnostic testing. 7) The chromosomal microarray test as an alternative to the conventional cytogenetic test is not recommended for all pregnant women who will undergo an invasive diagnostic testing. 8) Amniocentesis before 14 weeks of gestation is not recommended because it increases the risk of fetal loss and malformation. 9) CVS before 9 weeks of gestation is not recommended because it increases the risk of fetal loss and malformation. 10) Although the risk of fetal loss associated with invasive prenatal diagnostic testing (amniocentesis and CVS) may vary based on the proficiency of the operator, the risk of fetal loss due to invasive prenatal diagnostic testing is higher in twin pregnancies than in singleton pregnancies. 11) When a monochorionic twin is identified in early pregnancy and the growth and structure of both fetuses are consistent, an invasive prenatal diagnostic testing can be performed on one fetus alone. However, an invasive prenatal diagnostic testing is recommended for each fetus in cases of pregnancy conceived via in vitro fertilization, or in cases in which the growth of both fetuses differs, or in those in which at least one fetus has a structural abnormality. The guidelines were established and approved by the Korean Academy of Medical Sciences. This guideline is revised and presented every 5 years.     

Molecular genetic analysis reveals atypical confined placental mosaicism with a small supernumerary marker chromosome derived from chromosome 18: A clinical report of discordant results from three prenatal tests

We present a case with discordant results in three prenatal screening methods, with additional genetic analyses. Non-invasive prenatal testing (NIPT) was performed on a 41-year-old Japanese woman at 10 weeks of gestation, and the result was positive for trisomy 18 with high accuracy. Amniocentesis was performed at 16 weeks of gestation. However, the result showed 47,XX,+mar[16]/47,XX,+18[2]. Fetal examination by ultrasound revealed no malformations. After termination of the pregnancy, we performed additional genetic analyses, and confirmed the presence of confined placental mosaicism (CPM). Furthermore, a small supernumerary marker chromosome (sSMC) was detected in fetal cells, which was derived de novo from the centromere of chromosome 18. Single nucleotide polymorphism array analysis revealed that fetal chromosome 18 was inherited with maternal uniparental disomy, with a relatively large copy-neutral loss of heterozygosity, including its centromere. Our genetic analyses strongly indicated the cause of result discrepancy in prenatal testing as incomplete trisomy 18 rescue leading to atypical CPM with a sSMC. These findings also offer insight into the mechanisms by which chromosomal aberrations form during human oogenesis and embryogenesis.     

Comparison of next generation sequencing-based and methylated DNA immunoprecipitation-based approaches for fetal aneuploidy non-invasive prenatal testing

Over the past few years, many researchers have attempted to develop non-invasive prenatal testing methods in order to investigate the genetic status of the fetus. The aim is to avoid invasive procedures such as chorionic villus and amniotic fluid sampling, which result in a significant risk for pregnancy loss. The discovery of cell free fetal DNA circulating in the maternal blood has great potential for the development of non-invasive prenatal testing (NIPT) methodologies. Such strategies have been successfully applied for the determination of the fetal rhesus status and inherited monogenic disease but the field of fetal aneuploidy investigation seems to be more challenging. The main reason for this is that the maternal cell free DNA in the mother’s plasma is far more abundant, and because it is identical to half of the corresponding fetal DNA. Approaches developed are mainly based on next generation sequencing (NGS) technologies and epigenetic genetic modifications, such as fetal-maternal DNA differential methylation. At present, genetic services for non-invasive fetal aneuploidy detection are offered using NGS-based approaches but, for reasons that are presented herein, they still serve as screening tests which are not readily accessed by the majority of couples. Here we discuss the limitations of both strategies for NIPT and the future potential of the methods developed.