Clinical validation of a novel automated cell-free DNA screening assay for trisomies 21, 13, and 18 in maternal plasma

Early Non-Invasive Prenatal Testing at 6-9 Weeks of Gestation

Non-invasive prenatal testing (NIPT) is usually performed beyond 10 weeks of gestation, because earlier in pregnancy, the fetal fraction is low, resulting in failure to obtain reliable results. This study aimed to evaluate the clinical performance of NIPT earlier in pregnancy using a method for cell-free DNA (cfDNA) analysis that eliminates the need for polymerase chain reaction (PCR), DNA sequencing, or microarrays (Vanadis® system, PerkinElmer, Waltham, MA, USA). Cell-free DNA was extracted from the maternal plasma of 30 singleton pregnancies at 6-9 weeks of gestation (group 1) and at 11-14 weeks of gestation of the same patients (group 2). The mean crown-rump length (CRL) and gestational age in group A was 16.12 mm and that in group B was 61.45 mm. In group A, results were obtained in all, but one, cases (97%). From the remaining pregnancies, one miscarried at 8 weeks and, therefore, the follow-up NIPT at 12 weeks could not be performed. The fetal sex was diagnosed correctly in the 28 cases that had a successful early test, and the results were in accordance with the examination at 12 weeks. There were no cases of aneuploidies and disomy was diagnosed correctly in all. The "Vanadis" prenatal NIPT assay can successfully be used early during the first trimester at 6-9 weeks of gestation (early NIPT) to identify the fetal sex. Further studies are needed to explore the diagnostic potential for aneuploidies.

Cell-free DNA screening for common autosomal trisomies using rolling-circle replication in twin pregnancies

OBJECTIVE

To evaluate the performance of prenatal screening for common autosomal trisomies in twin pregnancies through the use of rolling-circle replication (RCR)-cfDNA as a first-tier test.

METHOD

Prospective multicenter study. Women who underwent prenatal screening for trisomy (T) 21, 18 and 13 between January 2019 and March 2022 in twin pregnancies were included. Patients were included in two centers. The primary endpoint was the rate of no-call results in women who received prenatal screening for common autosomal trisomies by RCR-cfDNA at the first attempt, compared to that in prospectively collected samples from 16,382 singleton pregnancies. The secondary endpoints were the performance indices of the RCR-cfDNA.

RESULTS

862 twin pregnancies underwent screening for T21, T18 and T13 by RCR-cfDNA testing at 10-33 weeks' gestation. The RCR-cfDNA tests provided a no-call result from the first sample obtained from the patients in 107 (0.7%) singleton and 17 (2.0%) twin pregnancies. Multivariable regression analysis demonstrated that significant independent predictors of test failure were twin pregnancy and in vitro fertilization conception. All cases of T21 (n = 20/862; 2.3%), T18 (n = 4/862; 0.5%) and T13 (n = 1/862; 0.1%) were correctly detected by RCR-cfDNA (respectively, 20, 4 and 1 cases). Sensitivity was 100% (95% CI, 83.1%-100%), 100% (95% CI 39.8%-100%) and 100% (95% CI 2.5%-100%) for T21, T18 and T13, respectively, in twin pregnancies.

CONCLUSION

The RCR-cfDNA test appears to have good accuracy with a low rate of no-call results in a cohort of twin pregnancies for the detection of the most frequent autosomal trisomies.

Cell-free DNA-based prenatal screening via rolling circle amplification: Identifying and resolving analytic issues

OBJECTIVE

A rolling circle amplification (RCA) based commercial methodology using cell-free (cf)DNA to screen for common trisomies became available in 2018. Relevant publications documented high detection but with a higher than expected 1% false positive rate. Preliminary evidence suggested assay variability was an issue. A multi-center collaboration was created to explore this further and examine whether subsequent manufacturer changes were effective.

METHODS

Three academic (four devices) and two commercial (two devices) laboratories provided run date, chromosome 21, 18, and 13 run-specific standard deviations, number of samples run, and reagent lot identifications. Temporal trends and between-site/device consistency were explored. Proportions of run standard deviations exceeding pre-specified caps of 0.4%, 0.4% and 0.6% were computed.

RESULTS

Overall, 661 RCA runs between April 2019 and July 30, 2022 tested 39,756 samples. In the first 24, subsequent 9, and final 7 months, proportions of capped chromosome 21 runs dropped from 39% to 22% to 6.0%; for chromosome 18, rates were 76%, 36%, and 4.0%. Few chromosome 13 runs were capped using the original 0.60%, but capping at 0.50%, rates were 28%, 16%, and 7.6%. Final rates occurred after reformulated reagents and imaging software modifications were fully implemented across all devices. Revised detection and false positive rates are estimated at 98.4% and 0.3%, respectively. After repeat testing, failure rates may be as low as 0.3%.

CONCLUSION

Current RCA-based screening performance estimates are equivalent to those reported for other methods, but with a lower test failure rate after repeat testing.

Overview of Noninvasive Prenatal Testing (NIPT) for the Detection of Fetal Chromosome Abnormalities; Differences in Laboratory Methods and Scope of Testing

Although nearly all noninvasive prenatal testing is currently based on analyzing circulating maternal cell-free DNA, the technical methods usedvary considerably. We review the different methods. Based on validation trials and clinical experience, there are mostly relatively small differences in screening performance for trisomies 21, 18, and 13 in singleton pregnancies. Recent reports show low no-call rates for all methods, diminishing its importance when choosing a laboratory. However, method can be an important consideration for twin pregnancies, screening for sex chromosome abnormalities, microdeletion syndromes, triploidy, molar pregnancies, rare autosomal trisomies, and segmental imbalances, and detecting maternal chromosome abnormalities.

Non-Invasive prenatal testing with rolling circle amplification: Real-world clinical experience in a non-molecular laboratory

BACKGROUND

Non-invasive prenatal testing (NIPT) using cell-free DNA (cfDNA) circulating in maternal blood provides a sensitive and specific screening technique for common fetal aneuploidies, but the high cost and workflow complexity of conventional methodologies limit its widespread implementation. A unique rolling circle amplification methodology reduces cost and complexity, providing a promising alternative for increased global accessibility as a first-tier test.

METHODS

In this clinical study, 8160 pregnant women were screened on the Vanadis system for trisomies 13, 18, and 21, and positive results were compared to clinical outcomes where available.

RESULTS

The Vanadis system yielded a 0.07% no-call rate, a 98% overall sensitivity, and a specificity of over 99% based on available outcomes.

CONCLUSION

The Vanadis system provided a sensitive, specific, and cost-effective cfDNA assay for trisomies 13, 18, and 21, with good performance characteristics and low no-call rate, and it eliminated the need for either next-generation sequencing or polymerase chain reaction amplification.

Next-Generation Digital Polymerase Chain Reaction: High-Dynamic-Range Single-Molecule DNA Counting via Ultrapartitioning

Digital PCR (dPCR) was first conceived for single-molecule quantitation. However, current dPCR systems often require DNA templates to share partitions due to limited partitioning capacities. Here, we introduce UltraPCR, a next-generation dPCR system where DNA counting is performed in a single-molecule regimen through a 6-log dynamic range using a swift and parallelized workflow. Each UltraPCR reaction is divided into >30 million partitions without microfluidics to achieve single template occupancy. Combined with a unique emulsion chemistry, partitions are optically clear, enabling the use of a three-dimensional imaging technique to rapidly detect DNA-positive partitions. Single-molecule occupancy also allows for more straightforward multiplex assay development due to the absence of partition-specific competition. As a proof of concept, we developed a 222-plex UltraPCR assay and demonstrated its potential use as a rapid, low-cost screening assay for noninvasive prenatal testing for as low as 4% trisomy fraction samples with high precision, accuracy, and reproducibility.

Positive predictive values and outcomes for uninformative cell-free DNA tests: An Italian multicentric Cytogenetic and cytogenomic Audit of diagnOstic testing (ICARO study)

OBJECTIVES

To establish the positive predictive values (PPV) of cfDNA testing based on data from a nationwide survey of independent clinical cytogenetics laboratories.

METHODS

Prenatal diagnostic test results obtained by Italian laboratories between 2013 and March 2020 were compiled for women with positive non-invasive prenatal tests (NIPT), without an NIPT result, and cases where there was sex discordancy between the NIPT and ultrasound. PPV and other summary data were reviewed.

RESULTS

Diagnostic test results were collected for 1327 women with a positive NIPT. The highest PPVs were for Trisomy (T) 21 (624/671, 93%) and XYY (26/27, 96.3%), while rare autosomal trisomies (9/47, 19.1%) and recurrent microdeletions (8/55, 14.5%) had the lowest PPVs. PPVs for T21, T18, and T13 were significantly higher when diagnostic confirmation was carried out on chorionic villi (97.5%) compared to amniotic fluid (89.5%) (p < 0.001). In 19/139 (13.9%), of no result cases, a cytogenetic abnormality was detected. Follow-up genetic testing provided explanations for 3/6 cases with a fetal sex discordancy between NIPT and ultrasound.

CONCLUSIONS

NIPT PPVs differ across the conditions screened and the tissues studied in diagnostic testing. This variability, issues associated with fetal sex discordancy, and no results, illustrate the importance of pre- and post-test counselling.

Increased nuchal translucency can be ascertained using transverse planes

BACKGROUND

The detection of increased nuchal translucency is crucial for the assessment risk of aneuploidies and other fetal anomalies.

OBJECTIVE

This study aimed to investigate the ability of a transverse view of the fetal head to detect increased fetal nuchal translucency at 11 to 13 weeks of gestation.

STUDY DESIGN

This was a prospective study enrolling a nonconsecutive series of women who attended our outpatient clinic from January 2020 to April 2021 for combined screening and were examined by operators certified by the Fetal Medicine Foundation. In each patient, nuchal translucency measurements were obtained both from a median sagittal view and from a transverse view. A second sonologist blinded to the results of the first examination obtained another measurement to assess intermethod and interobsever reproducibility.

RESULTS

A total of 1023 women were enrolled. An excellent correlation was found between sagittal and transverse nuchal translucency measurements, with a mean difference of 0.01 mm (95% confidence interval, -0.01 to 0.02). No systematic difference was found between the 2 techniques. The inter-rater reliability (intraclass correlation coefficient, 0.957; 95% confidence interval, 0.892-0.983) and intrarater reliability (intraclass correlation coefficient, 0.976; 95% confidence interval, 0.941-0.990) of axial measurements were almost perfect. Transverse measurements of 3.0 mm identified all cases with sagittal measurements of ≥3.0 with a specificity of 99.7%; transverse measurements of >3.2 mm identified all cases with sagittal measurements of 3.5 mm with a specificity of 99.7%. The time required to obtain transverse nuchal translucency measurements was considerably shorter than for sagittal measurements, particularly when the fetus had an unfavorable position.

CONCLUSION

When the sonogram is performed by an expert sonologist, the difference in nuchal translucency measurement obtained with a transverse or sagittal plane is minimal. Increased nuchal translucency can be reliably identified by using transverse views, and in some cases, this may technically be advantageous.

Assessment of a Simplified Cell-Free DNA Method for Prenatal Down Syndrome Screening

Background

Prenatal screening for common trisomies via cell-free (cfDNA) is usually implemented by technologies utilizing massively parallel sequencing, stringent environmental controls, complex bioinformatics, and molecular expertise. An alternative and less complex methodology utilizes rolling circle amplification (RCA). Further evaluation of its performance and related requirements are warranted.

Methods

At 16 sites, women at 10 to 20 weeks gestation provided informed consent, relevant information, and 2 to 3 blood samples. Samples shipped for testing were processed and stored. Women were enrolled at primary cfDNA screening, or following such screening at referral for diagnostic testing. RCA testing occurred post-enrollment, over 11 months. Diagnostic results and delivery notes determined clinical truth. Detection rates were based on confirmed trisomic pregnancies; false-positive rates were based on unaffected pregnancies from the general population.

Results

Detection rate for the common trisomies was 95.9% (117/122, 95% CI, 90.5%–98.5%); overall false-positive rate was 1.00% (22/2,205, 0.65%–1.51%). Test failure rate after repeat testing was 0.04%. When assay standard deviations were below pre-specified levels, the overall false-positive rate was much lower at 0.30% (P &lt; 0.001). Fetal sex calls were correct for 99.7%. One technician analyzed 560 samples over 2 weeks, a rate of 14 000/year.

Conclusions

Our assessment of this simplified cfDNA-based system for prenatal screening for common trisomies performed in a prenatal screening laboratory is encouraging. Improved detection, low failure rates and rapid reporting can be achieved by collecting 2 samples. Future priorities should include achieving higher run precision using a single collection tube.

Clinicaltrials.gov Registration Number: NCT03087357.

A Critical Evaluation of Validation and Clinical Experience Studies in Non-Invasive Prenatal Testing for Trisomies 21, 18, and 13 and Monosomy X

Non-invasive prenatal testing (NIPT) for trisomies 21, 18, 13 and monosomy X is widely utilized with massively parallel shotgun sequencing (MPSS), digital analysis of selected regions (DANSR), and single nucleotide polymorphism (SNP) analyses being the most widely reported methods. We searched the literature to find all NIPT clinical validation and clinical experience studies between January 2011 and January 2022. Meta-analyses were performed using bivariate random-effects and univariate regression models for estimating summary performance measures across studies. Bivariate meta-regression was performed to explore the influence of testing method and study design. Subgroup and sensitivity analyses evaluated factors that may have led to heterogeneity. Based on 55 validation studies, the detection rate (DR) was significantly higher for retrospective studies, while the false positive rate (FPR) was significantly lower for prospective studies. Comparing the performance of NIPT methods for trisomies 21, 18, and 13 combined, the SNP method had a higher DR and lower FPR than other methods, significantly so for MPSS, though not for DANSR. The performance of the different methods in the 84 clinical experience studies was consistent with validation studies. Clinical positive predictive values of all NIPT methods improved over the last decade. We conclude that all NIPT methods are highly effective for fetal aneuploidy screening, with performance differences across methodologies.

The History and Future of Basic and Translational Cell-Free DNA Research at a Glance

We discuss the early history of the structure of DNA and its involvement in gene structure as well as its mobility in and between cells and between tissues in the form of circulating cell-free DNA (cfDNA). This is followed by a view of the present status of the studies on cfDNA and clinical applications of circulating cell-free tumor DNA (ctDNA). The future developments and roles of ctDNA are also considered.

Cost of providing cell-free DNA screening for Down syndrome in Finland using different strategies

OBJECTIVES

A financial analysis is carried out to assess costs and benefits of providing cell-free DNA screening in Finland, using different strategies.

METHODS

Three cell-free DNA screening strategies are considered: Primary, all women; Secondary, those with positive Combined test; and Contingent, the 10-30% with the highest Combined test risks. Three costs are estimated: additional cost for 10,000 pregnancies compared with the Combined test; 'marginal' cost of avoiding a Down syndrome birth which occurs in a pregnancy that would have been false-negative using the Combined test; and marginal cost of preventing the iatrogenic loss of a non-Down syndrome birth which occurs in a pregnancy that would have been false-positive.

RESULTS

Primary cell-free DNA will require additional funds of €250,000. The marginal cost per Down syndrome birth avoided is considerably less than the lifetime medical and indirect cost; the marginal cost per unaffected iatrogenic fetal loss prevented is higher than one benefit measure but lower than another. If the ultrasound component of the Combined test is retained, as would be in Finland, the additional funds required rise to €992,000. Secondary cell-free DNA is cost-saving as is a Contingent strategy with 10% selected but whilst when 20-30% costs rise they are much less than for the Primary strategy and are cost-beneficial.

CONCLUSIONS

When considering the place of cell-free DNA screening it is important to make explicit the additional and marginal costs of different screening strategies and the associated benefits. Under most assumptions the balance is favorable for Contingent screening.

Clinical Validation of Fetal cfDNA Analysis Using Rolling-Circle-Replication and Imaging Technology in Osaka (CRITO Study)

BACKGROUND

Noninvasive prenatal genetic testing (NIPT) has been adopted as the first choice for aneuploidy screening. The purposes of this study were to investigate the accuracy of Vanadis^® NIPT (hereafter CRITO-NIPT) in order to gain a deeper insight into the reasons for discrepancies, as well as to discuss the role of fetal ultrasound.

METHODS

Between 2019 and 2020, CRITO-NIPT was performed in 1218 cases of patients who underwent CVS or amniocentesis after a detailed fetal ultrasound exam and genetic counseling. The CRITO-NIPT results were compared with the genetic results. In cases of test discrepancies, the placentae were collected for detailed genetic research, and the pre-procedure fetal ultrasound findings were referred to.

RESULTS

The positive predictive value of T21, T18, and T13 was 93.55%, 88.46%, and 100%, respectively. In 90% of the of false positive (FP) cases, the placentae were examined. In 75% of the CRITO FP-T21 cases, placental mosaicism, or a demised twin's T21, were confirmed. There were complicated mosaic cases, including tetrasomy 21/trisomy7 and monosomy 21/trisomy21 cases. In one of three no-call cases, an intermediate deletion of chromosome 13 was detected.

CONCLUSIONS

The CRITO study investigated the mechanism of false positives, and the detailed mechanisms in mosaic and no-call cases. There have hitherto been no reports that have provided insight by partitioning the placenta to compare the NIPT and invasive test results, nor that have provided detailed ultrasound findings in the cases of discordant results, revealing the demonstrated importance of, and necessity for, detailed ultrasonography. This article describes the potential of rolling-circle replication as a powerful biosensing platform, as well as the importance of examining the fetus in detail with ultrasound. However, we should remember that the potential applications raise ethical and social concerns that go beyond aneuploidy and its methodology.

Cell-free DNA screening for fetal aneuploidy using the rolling circle method: A step towards non invasive prenatal testing simplification

OBJECTIVE

To assess the efficacy of cell-free (cf)DNA screening for aneuploidy using the automated system based on rolling circle replication.

METHODS

A prospective study among women referred for invasive prenatal diagnosis between July 2018 and December 2019. The plasma fraction was extracted within 5 days from blood collection, stored at -20°C and cfDNA measured between January and December 2019.

RESULTS

A total of 805 women were recruited; 778 with singleton pregnancies and 27 twins. There were 48 Down syndrome, 25 Edwards syndrome and 3 Patau syndrome cases. Overall, the no-call rate was 2.6% (95% confidence interval 1.6%-3.9%) which reduced from 4.7% to 1.1% after relocation of the system (p < 0.002) to ensure a constant ambient temperature below 25°C. In singletons the Down syndrome detection rate (DR) was 100% (93%-100%) and false-positive rate (FPR) 0.14% (0.00%-0.79%). The Edwards syndrome DR was 96% (80%-100%) and FPR 0.78% (0.29%-1.7%). One false-positive had a confined placental trisomy 18 and the remaining five a z-score requiring sample repetition; all the false-positives occurred before system relocation (p < 0.005). Patau syndrome DR and FPR were 67% (9.4%-99%) and 0.26% (0.03%-0.95%).

CONCLUSION

The cfDNA rolling circle method yields similar results to other methods provided that room temperature is adequately controlled.

Assessment and Clinical Utility of a Non-Next-Generation Sequencing-Based Non-Invasive Prenatal Testing Technology

Background: Rolling-circle replication (RCR) is a novel technology that has not been applied to cell-free DNA (cfDNA) testing until recently. Given the cost and simplicity advantages of this technology compared to other platforms currently used in cfDNA analysis, an assessment of RCR in clinical laboratories was performed. Here, we present the first validation study from clinical laboratories utilizing RCR technology. Methods: 831 samples from spontaneously pregnant women carrying a singleton fetus, and 25 synthetic samples, were analyzed for the fetal risk of trisomy 21 (T21), trisomy 18 (T18) and trisomy 13 (T13), by three laboratories on three continents. All the screen-positive pregnancies were provided post-test genetic counseling and confirmatory diagnostic invasive testing (e.g., amniocentesis). The screen-negative pregnancies were routinely evaluated at birth for fetal aneuploidies, using newborn examinations, and any suspected aneuploidies would have been offered diagnostic testing or confirmed with karyotyping. Results: The study found rolling-circle replication to be a highly viable technology for the clinical assessment of fetal aneuploidies, with 100% sensitivity for T21 (95% CI: 82.35-100.00%); 100.00% sensitivity for T18 (71.51-100.00%); and 100.00% sensitivity for T13 analyses (66.37-100.00%). The specificities were >99% for each trisomy (99.7% (99.01-99.97%) for T21; 99.5% (98.62-99.85%) for T18; 99.7% (99.03-99.97%) for T13), along with a first-pass no-call rate of 0.93%. Conclusions: The study showed that using a rolling-circle replication-based cfDNA system for the evaluation of the common aneuploidies would provide greater accuracy and clinical utility compared to conventional biochemical screening, and it would provide comparable results to other reported cfDNA methodologies.

Evaluation of repeat testing of a non-sequencing based NIPT test on a Finnish general-risk population

Introduction

To evaluate the effect of repeating test failures using an automated, non‐sequencing based non‐invasive prenatal testing test on a general‐risk population in Finland.

Material and Methods

A total of 545 samples from women who represent the average‐risk population in Oulu, Finland were analyzed with Vanadis^® non‐invasive prenatal testing. Repeat testing of test failures was performed using a second sample. Results before and after repeat testing were compared with the reference outcome, as determined by clinical examination of neonates.

Results

There were eight test failures after first‐pass analysis, representing 1.5% of samples (95% CI 0.6%‐2.9%). Seven out of eight failures could be resolved by analysis of a second sample, thereby reducing the test failure rate from 1.5% to 0.2% (95% CI 0.0%‐1.0%).

Conclusions

Repeating test failures with a second plasma sample could significantly reduce the effective failure rate, thereby providing a way to effectively minimize test failures and further improving clinical utility and test performance.

Prenatal screening for trisomy 21: a comparative performance and cost analysis of different screening strategies

Background

Prenatal screening for chromosome aneuploidies have constantly been evolving, especially with the introduction of cell-free fetal DNA (cfDNA) screening in the most recent years. This study compares the performance, costs and timing of test results of three cfDNA screening implementation strategies: contingent, reflex and primary.

Methods

We modelled enhanced first trimester screening (eFTS) as the first-tier test in contingent or reflex strategies. cfDNA test was performed contingent on or reflex from eFTS results. A comparison was made between cfDNA screening using sequencing technology and Rolling Circle Amplification (RCA)/imaging solution. All model assumptions were based on results from previous publications or information from the Ontario prenatal screening population.

Results

At an eFTS risk cut-off of ≥1/1000, contingent and reflex cfDNA screening have the same detection rate (DR) (94%) for trisomy 21. Reflex cfDNA screening using RCA/Imaging solution provided the lowest false positive rate and cost. The number of women requiring genetic counselling and diagnostic testing was significantly reduced and women received their cfDNA screening result 9 days sooner compared with the contingent model. While primary cfDNA screening improved the trisomy 21 DR by 3–5%, it was more costly and more women required diagnostic testing.

Conclusion

Reflex cfDNA screening is the most cost-effective prenatal screening strategy. It can improve the efficiency of prenatal aneuploidy screening by reducing the number of patient visits and providing more timely results.

Update on noninvasive prenatal testing: A review based on current worldwide research

Eight years have passed since noninvasive prenatal testing (NIPT) was clinically evaluated and data on NIPT for trisomy 21, 18 and 13 were collected. The data revealed that NIPT is more accurate than conventional first-trimester screening. However, there is still insufficient data regarding the clinical use of NIPT results in detecting sex chromosome aneuploidies or whole-genome regions. NIPT is already being used as a clinical screening method globally. However, it is an unconfirmed diagnostic test and the results must be interpreted with caution as they may yield false negatives, false positives or inconclusive results. Therefore, the aim of this review is to highlight the current status of information, including the different methodologies, shortcomings and implications, regarding NIPT after its adoption worldwide. It is important to include genetic counseling when implementing NIPT. Going forward, the knowledge obtained to date, including the associated shortcomings, must be considered in evaluating the effectiveness of NIPT in detecting genetic abnormalities.

The fragmentation patterns of maternal plasma cell-free DNA and its applications in non-invasive prenatal testing

The discovery of cell-free DNA (cfDNA) in maternal plasma has opened up new promises for the development of non-invasive prenatal testing (NIPT). Application of cfDNA in NIPT of fetus diseases and abnormalities is restricted by the low amount of fetal DNA molecules in maternal plasma. Fetus-derived cfDNA in maternal plasma are shorter than maternal DNA, thus leveraging the maternal and fetus-derived cfDNA molecules size difference has become a novel and more accurate method for NIPT. However, multiple biological properties such as size distribution of plasma DNA, proportion of fetal-derived DNA and methylation levels in maternal plasma across different gestational ages still remain largely unknown. Further insights into the size distribution and fragmentation pattern of circulating plasma cfDNA will shed light on the origin and fragmentation mechanisms of cfDNA during physiological and pathological processes in prenatal diseases and enhance our ability to take the advantage of plasma cfDNA as a molecular diagnostic tool. In the review, we start by summarizing the research techniques for the determination of the fragmentation profiles of cfDNA in maternal plasma. We then summarize the main progress and findings in size profiles of maternal plasma cfDNA and cffDNA. Finally, we discuss the potential diagnostic applications of plasma cfDNA size profiling.

Clinical validation of a novel automated cell-free DNA screening assay for trisomies 21, 13, and 18 in maternal plasma

Objective

To evaluate clinical performance of a new automated cell‐free (cf)DNA assay in maternal plasma screening for trisomies 21, 18, and 13, and to determine fetal sex.

Method

Maternal plasma samples from 1200 singleton pregnancies were analyzed with a new non–sequencing cfDNA method, which is based on imaging and counting specific chromosome targets. Reference outcomes were determined by either cytogenetic testing, of amniotic fluid or chorionic villi, or clinical examination of neonates.

Results

The samples examined included 158 fetal aneuploidies. Sensitivity was 100% (112/112) for trisomy 21, 89% (32/36) for trisomy 18, and 100% (10/10) for trisomy 13. The respective specificities were 100%, 99.5%, and 99.9%. There were five first pass failures (0.4%), all in unaffected pregnancies. Sex classification was performed on 979 of the samples and 99.6% (975/979) provided a concordant result.

Conclusion

The new automated cfDNA assay has high sensitivity and specificity for trisomies 21, 18, and 13 and accurate classification of fetal sex, while maintaining a low failure rate. The study demonstrated that cfDNA testing can be simplified and automated to reduce cost and thereby enabling wider population‐based screening.

What is already known about this topic?

Maternal plasma cell‐free (cf)DNA analysis with next-generation sequencing has a high sensitivity and specificity for fetal trisomy 21 and other common autosomal trisomies.

A new amplification-free, nonsequencing, and targeted cfDNA assay has been developed.

Proof‐of‐principle analysis found the new assay has promising results in screening for trisomy 21.

What does this study add?

The new assay has high sensitivity and specificity for trisomies 21, 18, and 13 in singleton pregnancies.

It can accurately determine fetal sex.

It is suitable for use in biochemical screening laboratories since it is highly automated and does not require specialized personnel.