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BY 4.0 license Open Access Published by De Gruyter August 12, 2022

Non-invasive prenatal screening tests – update 2022

Elena Kypri, Marios Ioannides, Achilleas Achilleos, George Koumbaris, Philippos Patsalis and Markus Stumm
From the journal LaboratoriumsMedizin

Abstract

Since 2012, non-invasive prenatal testing (NIPT) using cell-free DNA from maternal plasma is applied all over the world as highly efficient first-line or contingent screening approach for trisomy 13, 18 and 21. With further technical development the screening has expanded to other genetic conditions such as sex chromosome anomalies (SCAs), rare autosomal trisomies (RATs), microdeletions/microduplications, structural chromosomal aberrations and monogenic diseases. Meanwhile, commercial providers are offering a number of different tests, with variable performance, the application of which needs to be carefully evaluated to apply to the true needs of clinical practice. In our review we present the different NIPT methodologies and discuss the main strengths and limitations in the context of providing a responsible pregnancy management.

Introduction

Non-invasive prenatal testing (NIPT) is a screening method for detecting potential fetal genetic abnormalities from cell-free DNA (cfDNA) in maternal circulation. NIPT analyses residual amounts of cfDNA that is circulating in the mother’s blood which consists of both maternal and fetal components [1]. NIPT is now widely adopted in the clinical setting as it provides no risk for the pregnancy compared to traditional invasive methods which entail a modest but significant risk of miscarriage of about 0.1–2% [2]. Furthermore, its accuracy is improved compared to other non-invasive screening approaches such as measurement of maternal serum biochemical markers combined with fetal ultrasound markers. NIPT has been endorsed by professional bodies and organizations as a primary screening method regardless of the pregnancy risk status [3] and is rapidly being adopted as a first choice for aneuploidy screening for trisomy 13, 18, 21. A number of NIPT tests based on whole genome and targeted methods employing Next Generation Sequencing (NGS) have been developed and applied in clinical practice [4], [5], [6], [7], [8]. With further technical developments the screening is expanded to other genetic conditions such as sex chromosome anomalies (SCAs), rare autosomal trisomies (RATs), microdeletions/microduplications, structural chromosomal aberrations and monogenic diseases. In this review we compare the different technologies that provide the framework for NIPT, discuss implementation, recommendations from professional societies and highlight important considerations for genetic counselling.

Current NIPT technologies

The discovery of cell-free fetal DNA (cffDNA) in the maternal circulation and the introduction of NGS has allowed the use and analysis of cffDNA in NIPT applications. The fetal fraction represents the percentage of fetal cfDNA in relation to the overall circulating cell-free DNA in maternal plasma, and it is a major determinant of assay sensitivity [9]. The average fetal fraction is 10–15% between 10 and 20 weeks of gestation [10]. Such retrievable quantities of cfDNA thus led to the use as an important screening tool in early pregnancy. The most common commercially available techniques that utilize cfDNA analysis are described herein with their corresponding strengths and limitations (Table 1).

Table 1:

NIPT technologies comparison.

Methodology Whole genome technology Target amplification SNP technology Target amplification array technology Target capture enrichment technology Rolling circle amplification technology
Trisomy 21 18 13
Sex chromosome aneuploidies ×
Microdeletions ×
RATs and SAs × × × ×
Fetal fraction measured and reported ×
Analysis of original cfDNA fragments × × ×
Twin pregnancies

Whole genome sequencing

Whole genome sequencing (WGS) was the first generation technology for NIPT that uses massively parallel shotgun sequencing (MPSS) to randomly sequence cfDNA extracted from a pregnant woman’s blood in a genome-wide manner [4, 5, 11]. This approach allows for tens of millions of short-sequence DNA fragments to be sequenced rapidly and simultaneously in a single run. The aneuploidy status of fetal chromosome of interest is determined by the number of sequence reads obtained from the chromosome of interest vs. the reads obtained from the reference chromosomes. Almost all MPSS based NIPT methods employ counting based (using read depth information) statistical methods to identify fetal chromosomal and sub-chromosomal copy number aberrations. As such, the main limitations comprise (i) amplification variability leading to GC content and mappability bias that result in variable ratios of reads between chromosomes of interest, i.e., accuracy of fetal aneuploidy detection is not the same for all chromosomes and (ii) the need for pre-determined cut-offs based on past data, in an attempt to alleviate the aforementioned biases. Furthermore, the number of samples run together is an important consideration with this technology, as a high level of multiplexing can place a limitation on the total number of sequence reads carried out on each sample resulting in a reduced read depth, which in consequence can also affect accuracy in fetal fraction estimation. On the contrary, Whole Genome based NIPT allows for a simpler and faster laboratory pipeline and low assay complexity as it does not require an enrichment step. Whole Genome NIPT testing allows for prenatal screening of aneuploidies 21, 18, and 13, SCAs and has expanded to detect partial duplications and deletions, structural aberrations and testing of Rare Autosomal Trisomies (RATs) [4, 5, 12], [13], [14], [15]. The positive predictive value for the latter conditions has been reported to be quite low while the clinical utility is highly debatable [16].

Targeted technologies

SNP-based NIPT technology

SNPs are genetic variations among individuals. SNP based NIPT techniques are targeted technologies that determine the difference between parent and child DNA, and the relative dosage of genetic variation is utilized to infer copy number. This approach involves a multiplex amplification of SNP sequences in a single PCR reaction carried out on the plasma DNA followed by next-generation sequencing [17]. cfDNA is amplified by PCR using the specific SNP targets. Following sequencing, a set of statistical hypotheses that represent the different possible fetal genotypes and fetal fraction values are tested within a Bayesian-based maximum likelihood statistical method to get the fetal fraction and copy number state of each chromosome of interest. The ability to selectively sequence specific regions of the genome in cfDNA allows for a focused analysis of clinically important chromosomes. This technology can be applied for the detection of trisomies 13, 18, 21, SCAs and microdeletion syndromes and has been expanded to screening of monogenic diseases. SNP based NIPT technologies allow the identification of triploidy and can also provide zygocity information in twin pregnancies [18]. The limitations of this technology include its high overall no-call rate and its inability to be applied to egg donation, surrogate pregnancies and consanguinity. Overall, SNP based NIPT is a highly validated technology, allows for high levels of multiplexing and can be easily scalable.

Microarray NIPT technology

In this technology, probes designed to target specific sequences of the genome are synthesized onto specific areas on the microarray. Targeted cfDNA fragments are amplified by PCR, tagged with a fluorescent probe and bind to complimentary sequences on the microarray. Deviations in expected fluorescent counts indicate relative chromosome representation and aneuploidy. Targeting of SNPs also allows for fetal fraction estimation. Similarly to MPSS based NIPT methods, enrichment biases resulting in variable metrics between chromosomes of interest are also present in microarray NIPT technologies. This technology allows for high levels of multiplexing and can be scalable and cost effective. This technology is currently available for the detection of trisomies 13, 18, 21, SCAs and Di George microdeletion syndrome [7].

Rolling Circle amplification NIPT technology

In the Rolling Circle amplification method, cfDNA fragments are hybridized to probes designed to form circular DNA complexes and replicate by a rolling mechanism to generate replication products. The DNA circles are copied approximately 1,000 times by rolling-circle-replication to generate fluorescently labelled molecules. A nano filter plate then captures labelled molecules for counting. Deviations in expected fluorescent counts indicate aneuploidy. A strength of this technology is that it offers a simpler cost-effective laboratory pipeline and assay complexity with faster turnaround times. This technology has an inherent major disadvantage of not being able to simultaneously measure the fetal faction, an important consideration affecting assay accuracy. This technology is currently available for the detection of trisomy 13, 18, 21 [19, 20].

TACS NIPT technology

TACS Technology uses synthetic long DNA probes called Target Capture Sequences (TACS) [6] that are specifically designed for selected regions of the genome using targeted enrichment and next generation sequencing (NGS) avoiding regions that potentially reduce the sensitivity and specificity of the test. A key feature of this technology is the enrichment of only a small portion of the genome which reduces the number of sequencing reads resulting in an uncompromised read depth and high levels of sample multiplexing overcoming the limitations of whole genome based NIPT. Furthermore, due to the high read-depth levels, this technology ensures a very accurate and robust fetal fraction estimation [6]. Unlike amplicon based NIPTs, it analyses the original cfDNA fragments extracted from the maternal blood, thus allowing the use of additional information to be incorporated in the bioinformatics analysis pipelines, i.e., allowing a more accurate alleviation of potential enrichment biases that can affect chromosomes representation in each sample. TACS technology can be easily scaled and tailored to the needs of the market. It is currently available for testing of trisomies 13, 18, 21, SCAs [21] and specific microdeletion syndromes [22].

Clinical implementation and management

Common aneuploidies

The use of NIPT screening for chromosomal abnormalities such as trisomy 21, 18, 13 has consistently increased in both low and high-risk populations. NIPT testing for chromosomes 13, 18 and 21 is highly reliable. According to a recent meta-analysis of NIPT screening using cfDNA in maternal blood in singleton pregnancies the detection rate (DR) was reported more than >99% for fetuses with trisomy 21, 98% for trisomy 18 and 99% for trisomy 13 at a combined False positive rate (FPR) of 0.13%. Specifically, the DRs and FPRs in singletons were reported at 99.7% and 0.04% for trisomy 21, 97.9% and 0.04% for trisomy 18, 99.0% and 0.04% for trisomy 13 [23]. Meta-analysis data assessing NIPT for common trisomies in twin pregnancies is still limited. Nevertheless, a recent study by Gil et al. revealed somewhat lower sensitivity and specificity. Specifically, the DRs and FPRs in twins were 98.2% and 0.05% for trisomy 21, 88.9% and 0.03% for trisomy 18 and 66.7% and 0.19% for trisomy 13 [24]. In addition to sensitivity and specificity, the positive and negative predictive values (PPV and NPV) are important clinical parameters. These values depend partly on the performance of the test, but also vary with the prevalence of the tested condition in the population. Thus, the PPV value is expected to be decreased in low risk population and should be considered when evaluating an NIPT result.

Sex chromosomes

In addition to common autosomal trisomies, NIPT has expanded for sex chromosome aneuploidies which include Turner (45, X), Klinefelter (47, XXY), Triple X (47, XXX) and 47, XYY and 48, XXYY constitutions. Although individually each condition is relatively rare, cumulatively SCAs occur in approximately 0.3% of all live births [25]. A meta-analysis by Gil et al. reported a DR for monosomy X varying between 66.7 and 100% and the FPR varied between 0 and 0.52%. The pooled weighted DR and FPR were 90.3% (95% CI, 85.7–94.2%) and 0.23% (95% CI, 0.14–0.34%), respectively [26]. There are known biological reasons that are responsible for discrepant NIPT results leading to a lower PPV, including confined placental mosaicism, true fetal mosaicism or mosaic maternal karyotype. In fact, as previously reported, monosomy X has a high incidence of CPM which explains why NIPT testing for monosomy X results have lower PPV. A study by Grati et al. using a retrospective analysis of 67,030 samples has indicated that the PPV is much lower for 45, X especially in cases without ultrasound anomalies which can be as low as 51% [2729].

Microdeletions and microduplications

The application of NGS technologies has further advanced the application of NIPT to microdeletions and microduplications [30]. In fact, about 1 in 1,000 births are affected with a microdeletion or microduplication syndrome, due to a small gain or loss of genetic material, regardless of maternal age. The most common microdeletion is 22q11.2 deletion syndrome also known as DiGeorge microdeletion, with an incidence of about 1 in 992 in low-risk population [31]. Many of these syndromes present with variable clinical phenotypes and lack characteristic ultrasound markers, therefore are often non-detectable by sonographic fetal screening. Traditionally the detection of sub-chromosomal deletions and duplications is performed by invasive testing of fetal genetic material using microarray technology. Recent technological advances have allowed microdeletion testing non-invasively. Nevertheless, there is still limited validation data regarding microdeletion NIPT performance. Many factors influence the PPV of NIPT for microdeletions, including the prevalence of the disorder in the population, size of the copy number variant, fetal fraction of the sample and laboratory methodology. Inevitably the detection of small-size aberrations requires high read depth to achieve statistical significance in a positive call. Current guidelines are divided regarding microdeletion testing, some stating that microdeletion testing should not be endorsed [32] while others endorsing screening following a comprehensive pre-test counselling [33, 34].

Rare autosomal aneuploidies

Rare autosomal aneuploidies (RATs) are chromosomal aneuploidies which involve chromosomes other than 13, 18, 21 and the sex chromosomes. RATs are most often confined to the placenta, specifically to the cytotrophoblastic tissue [16]. Genome wide screening applications have been applied to detect RATs. National Implementation studies of Genome-Wide NIPT screening as a first-Tier testing in a large cohort of samples confirmed a low PPV for RATs [30]. Trident-2 study has reported an overall PPV of 6%. The low PPV in NIPT for RATs confirms that most RATs are confined to the placenta. While the association of trisomy 16 with a higher risk of adverse pregnancy outcome is well established [35], this association remains controversial for the other RATs [16]. Currently, the clinical consequences of RATs are poorly studied and larger studies with follow-up information are required to determine the clinical significance. Furthermore, there are no clearly defined steps for patient management. It is evident that providing genome wide testing can be problematic from patient perspective as most RATs are expected to be mosaic and of unclear clinical significance and testing can lead to an unnecessary increase in invasive procedures [16].

Structural aberrations

The recent application of genome-wide NIPT screening studies has allowed the identification of structural aberrations [30]. National implementation studies of genome-wide NIPT screening have reported structural aberrations with a PPV of 32% [36]. This PPV is lower than what was described when applied to a previous cohort of high-risk pregnancies (PPV 50%) [36]. The identification of secondary findings and the debatable clinical significance, stress the necessity for the need of guidelines for counselling and clinical management.

The efforts to extend NIPT to as many genetic questions as possible and to implement it as a screening procedure must be critically questioned. Every additional test option leads to a cumulative increase in the false positive rate and thus also to a reduction in specificity. The direct consequence would then be an increase in the resulting invasive interventions and uncertainty among patients.

Monogenic disorders

Higher resolution analyses of cfDNA at the level of single genes and mutations are also offered by different laboratories [30]. The analysis of genetic variations which can be deduced based on the absence or presence of foreign alleles in the maternal plasma is highly reliable and in certain cases has reached the diagnostic level. Therefore, such analyses as Rhesus-D (RhD) blood typing [37] point mutations of paternal origin and de novo mutations [38], are defined as non-invasive prenatal diagnostic (NIPD). The detection of point mutations that derive from the mother is still challenging.

NIPT in monogenic diseases has already been demonstrated using approaches such as relative mutation dosage (RMD) for b-thalassemia [39], haemophilia [40] and sickle-cell disease [41]. Different studies have targeted SNPs for whole genome sequencing and relative haplotype dosage for congenital adrenal hyperplasia (CAH) [42] and b-thalassemia [43] as well as direct linear amplification and quantification for Wilson’s disease [44]. The use of high precision and high throughput technologies such as digital PCR, allowed the development of higher sensitivity assays for the detection of monogenic inherited mutant alleles in cfDNA [39]. It is important to note that parental haplotype is utilized to interpret the fetal inheritance pattern. Another proof of concept study indicated the feasibility of integrating three tests in a single NIPT for the detection of aneuploidies, large copy number variants (>20 Mb) and a limited number of single gene diseases utilizing capture enrichment. Nevertheless, additional technological optimizations are needed prior to implementation [45]. Furthermore, TACS technology has been utilized for the determination of the fetal risk for monogenic diseases based on parental carrier status, combining an extended carrier screening test with NIPT [46]. The progress achieved in NIPT and the increasing availability of NGS technologies has resulted in the initial successful attempts for non-invasive prenatal WGS [38] which in turn enables the genome-wide NIPT of monogenic diseases. While the first achievements of genome-wide monogenic NIPT have been published, this method has not yet become clinically applicable. This could be attributed to assay limitations, the need for more cost-effective options as well as improved computational methods [47].

General considerations in NIPT testing

The cell free DNA in maternal blood

The origin of cfDNA in maternal blood is a mixture of maternal (∼90%) and placental (∼10%) DNA fragments. That means, the ‘fetal’ DNA originates exclusively from the placenta, mainly from the syncytiotrophoblast layer [48]. The placental cfDNA is detectable in maternal blood from the 5th week after conception and the amount increases during pregnancy up to 20–30% in the third trimester. Following birth, the placental cfDNA is cleared from the maternal blood circulation within a few hours [49]. The fetal fraction is an important factor for test accuracy [50, 51]. Different tests have different thresholds for fetal fraction and published studies highlight a significant variation between methods [52]. It is now apparent that individual clinical laboratories should optimize their platform-specific fetal fraction estimation methods according to the lower limit of detection. It is also important that laboratories implement a robust quality assurance scheme and participate in external proficiency testing (ex. EMQN/EQA) to test for the whole analytical process. The fetal fraction can be affected by maternal parameters (e.g., obesity, autoimmune conditions, medications) or by the aneuploidy status of the placenta [49]. There are also emerging reports linking low molecular weight heparin (LMWH) with persistent low fetal fraction but the effect is currently not clear [9]. Furthermore, pregnancies with specific trisomies (e.g., trisomy 13 and 18) often have smaller placenta and therefore tend to also have lower fetal fraction [48]. Clinicians need to understand the biological influences on fetal fraction to be able to provide optimal post-test counselling. When NIPT results are inconclusive due to low fetal fraction, the clinician should be aware of several critical clinical implications. The options to bypass these problems are a re-collection at a later gestational stage (because the fetal fraction is increasing in ongoing pregnancies) or to go straight to an invasive diagnostic testing strategy (chorionic villi sampling or amniocentesis). Success of recollection with different technologies is reported to be high [41]. In this respect, it is important that the technology can estimate the precise fetal fraction in order to provide accurate information to the clinician for a re-draw recommendation. Thus, professional guidelines recommend that all laboratories should establish and monitor analytical and clinical validity for fetal fraction and should include a clearly visible fetal fraction on their report [33].

Twin gestations

NIPT is also of clinical importance in multiple gestations which pose considerably more difficult management issues, especially in relation to the risks of invasive procedures. Thus, recent studies have focused on the implementation of cfDNA analysis in this pregancy group. The dizygotic twin group poses additional challenges, because each fetus contributes different amounts of cfDNA in the maternal circulation [53]. Therefore, it is imperative to ensure that the lowest possible fetal fraction of each sample is considered for classification purposes, thus minimizing the possibility of incorrect classification that could arise from low proportions of fetal DNA by one of the two fetuses. In this respect, clinicians should evaluate the choice of NIPT testing so that they implement high fidelity NIPT testing which allows accurate fetal fraction quantification. In addition, it is important to consider that NIPT is not as accurate in twin gestations as it is in singleton pregnancies and thus this information should be incorporated into pre-test counselling for patients with multiple gestations [24, 53, 54].

Discordant result

There are different reasons for discordance between NIPT results and the genetic constitution of the fetus. The reasons could be separated into fetal/placental factors, vanishing twin pregnancies and maternal factors.

Fetal/placental factors

Because of the extra-embryonal origin, NIPT results harbor a risk for feto-placental discrepancies and this can lead to false positive or false negative results. Similar limitations have been known for many years in laboratories performing prenatal diagnostics on chorionic villi. Confined placental mosaicisms (CPMs) are reported in 1–2% of chorionic villi cases [27].

In most of these cases, a confined placental aneuploidy mosaicism may lead to a false positive NIPT result. Nevertheless, the reverse can also occur. For example, a postzygotic mitotic error can produce a fetal aneuploidy mosaicism, not present in the placenta, therefore not detectable by NIPT and leading to a false negative NIPT result [27, 55].

Vanishing twin

The interpretation of NIPT results is complex in the event of a vanished twin and should be interpreted with caution. It is possible that DNA from the demised fetus is still detectable for a prolonged time in the maternal blood leading to a false positive result, in the event that the diminished fetus was aneuploid. The reverse can also occur if a high fetal fraction from the vanished twin masks the DNA of the surviving fetus. Currently, it is unclear whether the size of a vanishing twin or the size of its amniotic cavity correlate with the amount of cell-free DNA in the maternal plasma. Furthermore, it needs to be clarified whether a vanishing twin event may lead to immediate flooding of specific cffDNA into the mother’s circulation. Further clinical studies monitoring the progress of a vanished twin are required to gain a better understanding [11, 55].

Maternal factors

Maternal factors leading to discrepant results include maternal aneuploidy (due to constitutive maternal mosaicism or malignancy), maternal CNVs or maternal transfusion or organ transplantation. Such conditions can distort the real chromosomal status, leading to false positive or false negative NIPT results [55] In regards to the above limitations, NIPT should be applied in the context of a screening test where positive results should always be confirmed using invasive testing with amniocentesis.

NIPT and first trimester screening (FTS)

Prenatal genetic screening and diagnostic testing options should be offered to all pregnant women [3] (ACOG 2020). NIPT is considered the most sensitive and specific screening test for the most common fetal aneuploidies. There are two main strategies to implement NIPT for early pregnancy aneuploidy screening. Each strategy has specific advantages and disadvantages.

Because cfDNA analysis is the most sensitive and specific screening test for common aneuploidies, NIPT is offered to all pregnant women, regardless of maternal age or background risk. Performed at 10th week of pregnancy as a first line screening test, the complete analysis and follow up can be managed in most cases in the first trimester. In test negative cases and in cases with test failures, further management can be oriented by the results of follow up ultrasound screening (FTS). Nevertheless, a baseline sonogram should always be performed before NIPT, because specific ultrasound findings are important for performing and interpreting the test (e.g., confirmation of viability, gestational age, number of embryos, and presence of vanishing twin). Patients with embryonal anomalies should be offered directly genetic counselling and invasive diagnostic testing instead of genetic screening [56].

Alternatively, NIPT is offered as contingent screening test to a group of pregnant women with an increased aneuploidy risk, e.g., by considering the results of FTS. This strategy further enhances the DR and decreases the FPR of NIPT, due to the higher incidence in that preselected group. This test strategy also maintains the additional information of FTS to screen for structural anomalies and placental disorders. The main disadvantage of this strategy is a possible shift of the diagnosis results to the second trimester for cases with test failures. NIPT currently allows reliable statements on the risk particularly, trisomy 21, 18, 13, but no statements on structural fetal malformations which make up the majority of perinatally relevant anomalies. Furthermore, most other chromosomal disorders and syndromal diseases cannot be detected. Therefore, all patients should be offered additionally a second trimester ultrasound (between 18th and 22nd week of gestation) for fetal structural defects, since these may occur with or without fetal aneuploidy [3, 57].

Genetic counseling

Every pregnant woman should make an informed choice regarding screening and/or diagnostic testing and advantages and limitations of diagnostic testing and NIPT should be clearly explained (Table 2). Therefore, patients should be counseled regarding their specific risk. Counseling should be performed in a clear, objective and non-directive fashion, allowing patients sufficient time to understand and make informed decisions regarding testing [3]. Pretest counseling should include information of the nature, significance and consequences of the genetic testing. After counseling, every patient has the right to pursue or decline prenatal genetic screening or diagnostic testing.

Table 2:

Comparison of prenatal screening vs. diagnostic testing.

Prenatal screening tests Prenatal diagnostic tests
  1. Non-invasive tests

  1. Definite answer, including karyotype. Small risk of false positive or negative results, depending on test type

  1. Applicable for all pregnancies

  1. Invasive tests

  1. No risk to the pregnant woman or fetus

  1. Small risk of miscarriage in singleton pregnancies

  1. Performed early during pregnancy

  1. Considerable risk of miscarriage in twin pregnancies

  1. Results are available fast

  1. Performed later during pregnancy

  1. Risk of being affected no definite answer

  1. Risk depends on practitioner and fetus (movement)

  1. All high-risk results have to be confirmed with a diagnostic test

  1. Small risk of infection

  1. Resting period recommended after procedure


Ultrasounds, serum screening (biochemical testing) NIPT CVS Amniocentesis

‘Traditional or Routine’ screening tests. Part of each country’s prenatal screening programs Newer test that analyses cell-free fetal DNA, which passes from the placenta into the maternal circulation Performed during weeks 11–14 of pregnancy, by taking a sample from the placenta Performed during weeks 15–20 of pregnancy, by taking a sample from the amniotic fluid
  1. Check for main chromosomal aneuploidies (T21, T18, T13)

  1. Can check for T21, T18, T13, and also for sex chromosome aneuploidies, and select microdeletions which have important clinical significance and prevalence in the population

  1. Check for physical abnormalities

  1. The most sensitive and specific screening test for common fetal aneuploidies (ACOG Practice Bulletin Number 226, 2020)

  1. Cannot identify other aneuploidies with critical significance and prevalence, such as sex chromosome aneuploidies and microdeletions

  1. Can be performed from 9–10 weeks of gestation

  1. High false positive rate (more referrals for diagnostic testing)

  1. Risk of not identifying affected pregnancies in younger patients


False positive and false negative results due to:

  1. Result depending on statistical variables such as maternal age, weight and smoking history (not pregnancy-specific)

  1. Risk of placenta mosaicism, maternal mosaicism or malignancy

  1. Risk of placenta mosaicism

Posttest counseling should clearly explain the test results and offer, if necessary, additional test options. Patients with a positive screening result should undergo additional ultrasound examinations with an opportunity for an adequate diagnostic follow up analysis. Patients with negative test results should be made aware, that the test result only decreases the risk for the tested conditions but does not ensure that the fetus is unaffected. Patients with no-call test results should be informed that test failure is associated with an increased aneuploidy risk and be offered comprehensive ultrasound evaluation and optionally diagnostic analysis.

In Germany, NIPT requires medical information and genetic counselling according to the Genetic Diagnosis Act (GenDG). According to the guidelines of the German Genetic Diagnostics Commission (GEKO), NIPT is not classified as prenatal risk assessment. NIPT is classified as prenatal genetic analysis for determining genetic properties. This classification requires a specific qualification level for specialized genetic counselling. The counseling aspect will be particularly important following the decision of the Federal Joint Committee (G-BA) for government-funded health insurance to cover NIPT for trisomies 21, 18, or 13, in “justified individual cases” and after counselling.

Global adoption of NIPT

NIPT is becoming one of the fastest spreading genetic technologies worldwide starting with a commercial implementation in the private sector prior to its global implementation. Recent, market analysis estimates that the NIPT market is rapidly growing at 12% compounded annual growth rate (CAGR) by 2030. America counts for the largest market share followed by Europe (Mordon Intelligence report 2020). In Europe, a number of countries have adopted NIPT into a national policy/program. Two countries (Belgium and the Netherlands) offer NIPT for all pregnant women, whereas most other European countries have implemented NIPT as an offer for higher risk women after first trimester screening. In the USA, there are no national consensus policies on the use of NIPT; however, NIPT is widely implemented through individual insurance companies and State Medicaid programs [58]. The implementation and uptake are influenced by a number of factors including the structure of the healthcare system, the existence of a public funding program for prenatal testing as well as sociocultural, legal and political issues that render the implementation of unified policies highly complex. Currently there is significant heterogeneity regarding the public provision, regulation and funding of prenatal screening programs. For example, England, France and Germany, three European countries that offer NIPT as a second-tier test, define the threshold for giving free access to NIPT differently, which clearly indicates the overall complexity. Importantly, the implementation through the public healthcare systems such as the ones adopted by Netherlands, Belgium, France, UK, Germany and many others will provide further insights into the practical and logistical issues, test uptake, conditions tested, outcomes and counseling considerations. It is crucial that countries develop frameworks at the national and international level to guide implementation and to ensure an effective approach to screening. These frameworks should include the arrangements for data collection and monitoring, quality assurance, education and training of professionals and information for the public. Due to the many ethical aspects of the topic, a broad societal dialogue and debate should take place with all relevant stakeholders. Particular attention should be paid on counselling issues and the provision of high-quality information and high-quality testing. Quality-assured education and continuous further training of the professional groups involved in counselling is evidently very crucial.

Conclusions

Despite the different technologies and the need for objective assay performance evaluation, careful result interpretation, the need for counseling and clinical management strategies, the application of NIPT has revolutionized prenatal screening of common aneuploidies and other conditions of clinical relevance. NIPT is a powerful tool that provides clinicians and prospective parents with important clinical information and empowers them to make informed decisions regarding pregnancy management. With further technological advances and responsible innovation, NIPT remains a promising screening avenue for the detection of additional genetic conditions.


Corresponding author: Markus Stumm, PD Dr rer. nat., Medicover Genetics GmbH, Plauener Straße 163-165, 13053 Berlin, Germany, E-mail:

  1. Research funding: None declared.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  3. Competing interests: EK, MI, AA, GK and PP are employed by NIPD Genetics which is a NIPT provider. MS is employed by Medicover Genetics which is a NIPT provider.

  4. Informed consent: Not applicable.

  5. Ethical approval: Not applicable.

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Received: 2022-02-25
Accepted: 2022-07-13
Published Online: 2022-08-12
Published in Print: 2022-08-26

© 2022 the author(s), published by De Gruyter, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 International License.

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