Analysis of cell-free DNA in maternal blood in screening for fetal aneuploidies: updated meta-analysis

Patient choice and clinical outcomes following positive noninvasive prenatal screening for aneuploidy with cell-free DNA (cfDNA)

OBJECTIVE

Evaluate patient choices and outcomes following positive cfDNA.

METHOD

Retrospective cohort study of women with positive cfDNA through two academic centers between March 2012 and December 2014. Patients were screened based on ACOG indications. Medical records reviewed for counseling, ultrasound findings, diagnostic testing, karyotype and outcome.

RESULTS

CfDNA was positive in 114 women; 105 singletons and 9 twin pairs. CfDNA was positive for autosomal trisomy (21, 18, 13) in 96 (84.2%) and sex chromosome aneuploidy in 18 (15.8%). Certified genetic counselors performed 95% of post-cfDNA counseling. Prenatal diagnostic testing was pursued by 71/114 (62%). Karyotype was available in 91/105 (86.7%) singletons and confirmed aneuploidy in 75/91 (82.4%); the PPV of cfDNA with any ultrasound finding was 93.6% versus 58.6% without a finding. An abnormal sonographic finding was seen in 4/16 (25%) singletons with false positive cfDNA. Fetal termination occurred in 53/79 (67%) singletons and 3/5 (60%) twins with prenatal abnormal or unknown karyotype for autosomal trisomy. Eleven fetuses (11/56, 19.6%) were terminated for suspected autosomal trisomy without karyotype confirmation.

CONCLUSION

Patient choices following positive cfDNA are varied. Ultrasound modifies the PPV of cfDNA. Termination rates for aneuploidy are not higher than historical controls. Recommendation for karyotype confirmation prior to termination is not universally followed. © 2016 John Wiley & Sons, Ltd.

Women's Experiences and Preferences for Service Delivery of Non-Invasive Prenatal Testing for Aneuploidy in a Public Health Setting: A Mixed Methods Study

Non-invasive prenatal testing (NIPT) for aneuploidy is currently only available in the UK through the private sector outside of the research arena. As part of an implementation study in the UK National Health Service we conducted a mixed methods study to assess women’s experience of being offered NIPT using validated measures of decisional conflict, decisional regret and anxiety. Clinical service preferences were also explored. Women with a Down syndrome screening risk >1:1000 were invited to take part in the study and offered NIPT, NIPT and invasive testing (for women with a risk above 1:150) or no further testing. A cross-sectional survey and semi-structured interviews were conducted at two time points; at the time of testing and one month following receipt of results (or equivalent for NIPT decliners). In total, 845 questionnaires and 81 interviews were analysed. The main motivation to accept NIPT was for reassurance (30.8%). Decisional conflict occurred in a minimal number of cases (3.8%), however, none of the participants experienced decisional regret. Around a third (29.9%) of women had elevated anxiety at the time of testing, including intermediate risk women who traditionally would not be offered further testing (54.4% high risk; 20.1% medium risk), a finding supported through the qualitative interviews where prolonged or additional anxiety was found to occur in some medium risk cases. Women were overwhelmingly positive about the opportunity to have a test that was procedurally safe, accurate, reduced the need for invasive testing and identified cases of Down syndrome that might otherwise have been missed. Reassurance was identified as the main motivator for accepting NIPT, particularly amongst medium risk women, with high risk women inclined to accept NIPT to inform decisions around invasive testing. The current turnaround time for test result was identified as a key limitation. All the women interviewed thought NIPT should be adopted as part of NHS clinical practice, with the majority favouring NIPT offered as a first-line test. Our study highlights the potential that NIPT has to positively impact women’s experience of prenatal testing for aneuploidy.

Inverted Pyramid of Care

First-trimester pregnancy evaluation using fetal and maternal parameters not only allows for diagnoses to be made early in gestation but can also assess the risk of complications that become clinically evident later in pregnancy. This evaluation makes it possible for pregnancy care to be individualized. In select cases, treatment that reduces the risk of complications can be started early in pregnancy. Even though cell free DNA is a significant advance in diagnosing fetal aneuploidy, the combination of first-trimester ultrasound and maternal serum biochemistries casts a much wider diagnostic net; therefore, the 2 technologies are best used in combination.

Strategies for Implementing Cell-Free DNA Testing

Maternal plasma cell-free (cf) DNA testing has higher discriminatory power for aneuploidy than any conventional multi-marker screening test. Several strategies have been suggested for introducing it into clinical practice. Secondary cfDNA, restricted only to women with positive conventional screening test, is generally cost saving and minimizes the need for invasive prenatal diagnosis but leads to a small loss in detection. Primary cfDNA, replacing conventional screening or retaining the nuchal translucency scan, is not currently cost-effective for third-party payers. Contingent cfDNA, testing about 20% of women with the highest risks based on a conventional test, is the preferred approach.

Novel Epigenetic Markers on Chromosome 21 for Noninvasive Prenatal Testing of Fetal Trisomy 21

Until now, fetal placenta-specific epigenetic markers for noninvasive prenatal testing of fetal trisomy 21 (T21) have been identified based only on differences in tissue-specific epigenetic characteristics between placenta and maternal blood, but these characteristics have not been validated in T21 placenta. We aimed to discover novel epigenetic markers on chromosome 21 that show a hypermethylated pattern in fetal placenta compared with blood, regardless of the presence of T21. We performed a high-resolution tiling array analysis of chromosome 21 using the methylated-CpG binding domain protein-based method. We identified 93 epigenetic regions that showed fetal placenta-specific differential methylation patterns; among these, three regions showed fetal placenta-specific methylation patterns in T21 placenta samples. The methylation patterns of these three regions in the array were confirmed by bisulfite direct sequencing. The three regions were detectable in first-trimester maternal plasma. Moreover, a combination of their methylation ratio achieved high diagnostic accuracy for noninvasive prenatal testing of fetal T21 by further statistical analysis. These three novel regions with fetal placenta-specific differential methylation patterns on chromosome 21 were identified irrespective of the presence of T21. Our findings suggest that epigenetic characteristics of markers according to the presence or absence of T21 should be considered in the development of noninvasive prenatal testing of fetal T21 using fetal placenta-specific epigenetic markers.

Validation of two-channel sequencing-by-synthesis for noninvasive prenatal testing of fetal whole and partial chromosome aberrations

OBJECTIVE

To validate Illumina's two-channel NextSeq 500 sequencing system for noninvasive prenatal testing (NIPT) of fetal whole chromosome and partial aberrations.

METHODS

A total of 162 plasma samples, previously sequenced for NIPT on a SOLiD 5500xl platform, were sequenced on the NextSeq 500 using 75-bp single-end sequencing, followed by analysis using the WISECONDOR algorithm.

RESULTS

For whole chromosome aneuploidy detection, all samples were classified correctly (in total 3× T13, 3× T18, 8× T21 and 145× euploid). Three partial aberrations (36-Mb terminal loss of 5p, 14-Mb gain on 18p and 33-Mb terminal loss of 13q) were also correctly identified. Fetal fractions in 34 male samples sequenced on both the SOLiD 5500xl and NextSeq 500 platform showed no significant difference. To test robustness, two sample sets, containing both euploid and aneuploid samples, were sequenced on different NextSeq 500 machines, revealing identical results. With unchanged laboratory flow, the NIPT turnaround time could be reduced from 15-16 calendar days to 7-8 calendar days, after switching from the SOLiD 5500xl to the NextSeq 500 platform.

CONCLUSIONS

The NextSeq 500 platform can be used for NIPT to detect both whole and partial chromosome aberrations. It has fast turnaround times and is suitable for mid-sized laboratories.

Clinical evaluation of the IONA test: a non-invasive prenatal screening test for trisomies 21, 18 and 13

OBJECTIVE

To evaluate the clinical accuracy of the IONA® test for aneuploidy screening.

METHODS

This was a multicenter blinded study in which plasma samples from pregnant women at increased risk of trisomy 21 underwent cell-free DNA analysis utilizing the IONA test. For each sample, the IONA software generated a likelihood ratio and a maternal age-adjusted probability risk score for trisomies 21, 18 and 13. All results from the IONA test were compared against accepted diagnostic karyotyping.

RESULTS

A total of 442 maternal samples were obtained, of which 437 had test results available for analysis and assessment of clinical accuracy. The IONA test had a detection rate of 100% for trisomies 21 (n = 43; 95% CI, 87.98-100%), 18 (n = 10; 95% CI, 58.72-100%) and 13 (n = 5; 95% CI, 35.88-100%) with cut-offs applied to likelihood ratio (cut-off > 1 considered high risk for trisomy) and probability risk score incorporating adjustment for maternal age (cut-off ≥ 1/150 considered high risk for trisomy). The false-positive rate (FPR) was 0% for trisomies 18 and 13 with both analysis outputs. For trisomy 21, a FPR of 0.3% was observed for the likelihood ratio, but became 0% with adjustment for maternal age.

CONCLUSION

This study indicates that the IONA test is suitable for trisomy screening in a high-risk screening population. The result-interpretation feature of the IONA software should facilitate wider implementation, particularly in local laboratories, and should be a useful addition to the current screening methods for trisomies 21, 18 and 13.

IONA test for first-trimester detection of trisomies 21, 18 and 13

OBJECTIVE

To assess the potential performance of screening for fetal trisomies 21, 18 and 13 by cell-free DNA (cfDNA) analysis of maternal blood using the IONA® test.

METHODS

This was a nested case-control study of cfDNA analysis of maternal plasma using the IONA test. Samples were obtained at 11-13 weeks' gestation, before chorionic villus sampling, from 201 euploid pregnancies, 35 with trisomy 21, four with trisomy 18 and two with trisomy 13. Laboratory personnel were blinded to the fetal karyotype.

RESULTS

Probability scores for trisomies 21, 18 and 13 were given for 241/242 samples analyzed. No probability score was provided for one (0.5%) euploid pregnancy because of low fetal fraction. In all 35 cases of trisomy 21 the probability score for trisomy 21 was > 95% and the scores for trisomies 18 and 13 were ≤ 0.0001%. In all four cases of trisomy 18, the probability score for trisomy 18 was > 77% and the scores for trisomies 21 and 13 were ≤ 0.0001%. In the two cases of trisomy 13, the probability score for trisomy 13 was > 59% and the scores for trisomies 21 and 18 were ≤ 0.0001%. In the 200 euploid pregnancies with a test result, the probability score was < 0.08% for trisomy 21, < 0.001% for trisomy 18 and < 0.002% for trisomy 13. Therefore, the IONA test detected 100% of all three trisomies, with a false-positive rate of 0%.

CONCLUSION

The IONA test successfully differentiated all cases of trisomies 21, 18 and 13 from euploid pregnancies.

Antenatal reflex DNA screening for trisomy 18 and trisomy 13 in addition to Down's syndrome

OBJECTIVE

Antenatal reflex DNA screening for Down's syndrome has a high screening performance. We aimed to determine the performance of trisomy 18 and trisomy 13 reflex DNA screening when added to Down's syndrome screening.

METHODS

In our modelled screening protocol, women provide two samples: a serum sample for a Combined test and a plasma sample for a possible DNA test. Women with Down's syndrome, trisomy 18, or trisomy 13 Combined test risks above a single cut-off have a reflex DNA test using the plasma sample, without the need to recall them to collect another sample and provide counselling. Women with a failed DNA test (after a second attempt using a fresh plasma sample) have an Integrated test, and are classified as positive if any of the Down's syndrome, trisomy 18, or trisomy 13 Integrated test risks are greater than 1 in 25.

RESULTS

At 1 in 800 term risk cut-offs for Down's syndrome, trisomy 18, and trisomy 13, an estimated 10% of women are reflexed to DNA screening, yielding a 91% Down's syndrome detection rate, an 89% trisomy 18 detection rate, and a 79% trisomy 13 detection rate for a 0.05% false-positive rate. At a 1 in 1900 term risk cut-off for Down's syndrome, trisomy 18, or trisomy 13, an estimated 20% of women are reflexed to DNA screening, and this yields a 94% Down's syndrome detection rate, a 92% trisomy 18 detection rate, and an 84% trisomy 13 detection rate for a 0.10% false-positive rate.

CONCLUSION

Reflex DNA screening for trisomies 18 and 13 can be usefully added to reflex DNA screening for Down's syndrome.

Accuracy of non-invasive prenatal testing using cell-free DNA for detection of Down, Edwards and Patau syndromes: a systematic review and meta-analysis

OBJECTIVE

To measure test accuracy of non-invasive prenatal testing (NIPT) for Down, Edwards and Patau syndromes using cell-free fetal DNA and identify factors affecting accuracy.

DESIGN

Systematic review and meta-analysis of published studies.

DATA SOURCES

PubMed, Ovid Medline, Ovid Embase and the Cochrane Library published from 1997 to 9 February 2015, followed by weekly autoalerts until 1 April 2015.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

English language journal articles describing case-control studies with ≥ 15 trisomy cases or cohort studies with ≥ 50 pregnant women who had been given NIPT and a reference standard.

RESULTS

41, 37 and 30 studies of 2012 publications retrieved were included in the review for Down, Edwards and Patau syndromes. Quality appraisal identified high risk of bias in included studies, funnel plots showed evidence of publication bias. Pooled sensitivity was 99.3% (95% CI 98.9% to 99.6%) for Down, 97.4% (95.8% to 98.4%) for Edwards, and 97.4% (86.1% to 99.6%) for Patau syndrome. The pooled specificity was 99.9% (99.9% to 100%) for all three trisomies. In 100,000 pregnancies in the general obstetric population we would expect 417, 89 and 40 cases of Downs, Edwards and Patau syndromes to be detected by NIPT, with 94, 154 and 42 false positive results. Sensitivity was lower in twin than singleton pregnancies, reduced by 9% for Down, 28% for Edwards and 22% for Patau syndrome. Pooled sensitivity was also lower in the first trimester of pregnancy, in studies in the general obstetric population, and in cohort studies with consecutive enrolment.

CONCLUSIONS

NIPT using cell-free fetal DNA has very high sensitivity and specificity for Down syndrome, with slightly lower sensitivity for Edwards and Patau syndrome. However, it is not 100% accurate and should not be used as a final diagnosis for positive cases.

TRIAL REGISTRATION NUMBER

CRD42014014947.

[Analysis of cell-free DNA in maternal blood for detection of fetal trisomy 21 in high-risk population: Couples acceptance and grounds for refusal]

OBJECTIVES

To assess the determinants associated with the use of analysis of cell-free DNA in maternal blood for detection of trisomy 21 in high-risk women.

MATERIALS AND METHODS

Prospective study conducted in a single center between July 15, 2014 and December 15, 2014 on 99 consecutive women with increased risk of trisomy 21 above 1/250.

RESULTS

Analysis of cell-free DNA in maternal blood for detection of fetal trisomy 21 was proposed to 95 women out of 99, among them, 43 women (45.3%) required the test. Among these 43 women, 17 (38.6%) had a higher socio-economic status versus 10 (19.2%) among the women who did not request the test (P=0.03). The most common reason given by the 52 women who did not request the analysis of cell-free DNA was the cost, for 30 of them (57.7%), then because the test was not providing certainty for the diagnostic of trisomy 21 for 23 women (44.2%).

CONCLUSION

Analysis of cell-free DNA on maternal blood for detection of trisomy 21 does not seem accepted by the majority of women. The cost is probably the main reason for not using this test, but it seems that the lack of diagnostic certainty is also an obstacle for some women.

First trimester screening cut-offs for noninvasive prenatal testing as a contingent screen: Balancing detection and screen-positive rates for trisomy 21

OBJECTIVE

To provide data on how screen-positive and detection rates of first trimester prenatal screening for fetal Down syndrome vary with changes in the risk cut-off and maternal age to inform contingency criteria for publicly funded noninvasive prenatal testing.

MATERIALS AND METHODS

First trimester screening and diagnostic data were collected for all women attending for first trimester fetal aneuploidy screening in Western Australia between 2005 and 2009. Prenatal screening and diagnostic data were linked to pregnancy outcomes, including data from the Midwives' Notification System and the Western Australian Registry of Developmental Anomalies. The prevalence of Down syndrome and performance of screening by risk cut-off and/or for women >35 years were analysed.

RESULTS

The current screening risk cut-off of 1:300 has screen-positive and detection rates of 3.5% and 82%. The screen-positive rate increases by 0.7-0.8% for each 100 point change in risk, up to 19.2% at 1:2500 (96% detection rate). Including all women >35 years as screen positive would increase the screen-positive rate and detection rates to 30.2% and 97.2%.

CONCLUSION

Variation in screening risk cut-off and the use of maternal age to assess eligibility for noninvasive testing could significantly impact the demand for, and cost of, the test. A contingent first trimester screening approach for risk assessment is superior to the use of a combination of screening and maternal age alone. These data will inform decisions regarding the criteria used to determine eligibility for publicly funded noninvasive prenatal testing.

Maternal Plasma DNA and RNA Sequencing for Prenatal Testing

Cell-free DNA (cfDNA) testing has recently become indispensable in diagnostic testing and screening. In the prenatal setting, this type of testing is often called noninvasive prenatal testing (NIPT). With a number of techniques, using either next-generation sequencing or single nucleotide polymorphism-based approaches, fetal cfDNA in maternal plasma can be analyzed to screen for rhesus D genotype, common chromosomal aneuploidies, and increasingly for testing other conditions, including monogenic disorders. With regard to screening for common aneuploidies, challenges arise when implementing NIPT in current prenatal settings. Depending on the method used (targeted or nontargeted), chromosomal anomalies other than trisomy 21, 18, or 13 can be detected, either of fetal or maternal origin, also referred to as unsolicited or incidental findings. For various biological reasons, there is a small chance of having either a false-positive or false-negative NIPT result, or no result, also referred to as a "no-call." Both pre- and posttest counseling for NIPT should include discussing potential discrepancies. Since NIPT remains a screening test, a positive NIPT result should be confirmed by invasive diagnostic testing (either by chorionic villus biopsy or by amniocentesis). As the scope of NIPT is widening, professional guidelines need to discuss the ethics of what to offer and how to offer. In this review, we discuss the current biochemical, clinical, and ethical challenges of cfDNA testing in the prenatal setting and its future perspectives including novel applications that target RNA instead of DNA.

Clinical implementation of routine screening for fetal trisomies in the UK NHS: cell-free DNA test contingent on results from first-trimester combined test

OBJECTIVES

Cell-free DNA (cfDNA) analysis of maternal blood for detection of trisomies 21, 18 and 13 is superior to other methods of screening but is expensive. One strategy to maximize performance at reduced cost is to offer cfDNA testing contingent on the results of the first-trimester combined test that is used currently. The objectives of this study were to report the feasibility of implementing such screening, to examine the factors affecting patient decisions concerning their options for screening and decisions on the management of affected pregnancies and to report the prenatal diagnosis of fetal trisomies and outcome of affected pregnancies following the introduction of contingent screening.

METHODS

We examined routine clinical implementation of contingent screening in 11,692 singleton pregnancies in two National Health Service (NHS) hospitals in the UK. Women with a risk ≥ 1 in 100 (high-risk group) were offered options of invasive testing, cfDNA testing or no further testing, and those with a risk between 1 in 101 and 1 in 2500 (intermediate-risk group) were offered cfDNA testing or no further testing. The trisomic status of the pregnancies was determined by prenatal or postnatal karyotyping or by examination of the neonates.

RESULTS

In the study population of 11,692 pregnancies, there were 47 cases of trisomy 21 and 28 of trisomies 18 or 13. Screening with the combined test followed by invasive testing for all patients in the high-risk group potentially could have detected 87% of trisomy 21 and 93% of trisomies 18 or 13, at a false-positive rate of 3.4%; the respective values for cfDNA testing in the high- and intermediate-risk groups were 98%, 82% and 0.25%. However, in the high-risk group, 38% of women chose invasive testing and 60% chose cfDNA testing; in the intermediate-risk group 92% opted for cfDNA testing. A prenatal diagnosis was made in 43 (91.5%) pregnancies with trisomy 21 and all pregnancies with trisomies 18 or 13. In many affected pregnancies the parents chose to avoid testing or termination and 32% of pregnancies with trisomy 21 resulted in live births.

CONCLUSIONS

Screening for fetal trisomies by cfDNA analysis of maternal blood, contingent on the results of the combined test, can be implemented easily in routine clinical practice. In the high-risk group from the combined test, most but not all women chose cfDNA testing rather than invasive testing. Performance of screening for trisomy 21 was superior by the cfDNA test than by the combined test. However, prenatal detection of trisomies and pregnancy outcome depend not only on performance of screening tests but also on parental choice.

Cell-Free Fetal DNA Testing for Prenatal Diagnosis

Prenatal diagnosis and screening have undergone rapid development in recent years, with advances in molecular technology driving the change. Noninvasive prenatal testing (NIPT) for Down syndrome as a highly sensitive screening test is now available worldwide through the commercial sector with many countries moving toward implementation into their publically funded maternity systems. Noninvasive prenatal diagnosis (NIPD) can now be performed for definitive diagnosis of some recessive and X-linked conditions, rather than just paternally inherited dominant and de novo conditions. NIPD/T offers pregnant couples greater choice during their pregnancy as these safer methods avoid the risk of miscarriage associated with invasive testing. As the cost of sequencing falls and technology develops further, there may well be potential for whole exome and whole genome sequencing of the unborn fetus using cell-free DNA in the maternal plasma. How such assays can or should be implemented into the clinical setting remain an area of significant debate, but it is clear that the progress made to date for safer prenatal testing has been welcomed by expectant couples and their healthcare professionals.

Preferences for prenatal tests for Down syndrome: an international comparison of the views of pregnant women and health professionals

Non-invasive prenatal testing is increasingly available worldwide and stakeholder viewpoints are essential to guide implementation. Here we compare the preferences of women and health professionals from nine different countries towards attributes of non-invasive and invasive prenatal tests for Down syndrome. A discrete choice experiment was used to obtain participants' stated preference for prenatal tests that varied according to four attributes: accuracy, time of test, risk of miscarriage, and type of information. Pregnant women and health professionals were recruited from Canada, Denmark, Iceland, Israel, Italy, the Netherlands, Portugal, Singapore, and the United Kingdom. A total of 2666 women's and 1245 health professionals' questionnaires were included in the analysis. Differences in preferences were seen between women and health professionals within and between countries. Overall, women placed greater emphasis on test safety and comprehensive information than health professionals, who emphasised accuracy and early testing. Differences between women's and health professionals' preferences are marked between countries. Varied approaches to implementation and service delivery are therefore needed and individual countries should develop guidelines appropriate for their own social and screening contexts.

Changing to NIPT as a first-tier screening test and future perspectives: opinions of health professionals

OBJECTIVE

The aim of this study was to investigate health professionals' opinions toward offering noninvasive prenatal testing (NIPT) as first-tier screening test regardless of pregnant women's risk, and toward a potential broader range of disorders.

METHODS

A questionnaire completed by obstetric health professionals (n = 240) after an in-service NIPT training in the West and North of the Netherlands.

RESULTS

The majority (72%) of respondents favored replacing first-trimester combined test (FCT) by NIPT, although 43% preferred to maintain nuchal translucency measurement. Many respondents believed that replacing FCT by NIPT would only have advantages (57%), would lead to more pregnant women opting for prenatal testing (69%), and would simplify counseling (47%). Differences in attitudes toward counseling between health professionals were observed. When considering NIPT to screen for broader range of disorders, the majority (92%) thought that this should include disorders characterized by neonatal death, whereas 52% of the respondents favored testing for fetomaternal risk factors. Overall, 46% thought screening should be offered as a fixed list of disorders.

CONCLUSION

Most health professionals favor NIPT instead of FCT but prefer to maintain nuchal translucency measurement. If NIPT becomes available as a first-tier screening test, attention remains necessary to ensure that pregnant women make well-informed decisions in line with the aim of prenatal screening.

Clinical performance of non-invasive prenatal testing (NIPT) using targeted cell-free DNA analysis in maternal plasma with microarrays or next generation sequencing (NGS) is consistent across multiple controlled clinical studies

Objective

To evaluate the clinical performance of non‐invasive prenatal testing for trisomy 21, 18, and 13 using targeted cell‐free DNA (cfDNA) analysis.

Methods

Targeted cfDNA analysis using DANSR™ and FORTE™ with microarray quantitation was used to evaluate the risk of trisomy 21, 18, and 13 in blinded samples from 799 singleton, twin, natural, and IVF pregnancies. Subjects either had fetal chromosome evaluation by karyotype, FISH, QF‐PCR, or karyotype for newborns with suspected aneuploidy at birth. The results of targeted cfDNA analysis were compared to clinical genetic testing outcomes to assess clinical performance.

Results

Targeted cfDNA analysis with microarray quantification identified 107/108 trisomy 21 cases (99.1%), 29/30 trisomy 18 cases (96.7%), and 12/12 trisomy 13 cases (100%). The specificity was 100% for all three trisomies. Combining this data with all published clinical performance studies using DANSR/FORTE methodology for greater than 23 000 pregnancies, the sensitivity of targeted cfDNA analysis was calculated to be greater than 99% for trisomy 21, 97% for trisomy 18, and 94% for trisomy 13. Specificity for each trisomy was greater than 99.9%.

Conclusion

Targeted cfDNA analysis demonstrates consistently high sensitivity and extremely low false positive rates for common autosomal trisomies in pregnancy across quantitation platforms. © 2015 Ariosa Diagnostics Inc. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

What's already known about this topic?

NIPT using targeted cfDNA analysis with NGS has high sensitivity and specificity for fetal trisomy 21 and other autosomal trisomies.

What does this study add?

This study establishes the high sensitivity and specificity of NIPT using targeted cfDNA analysis with a microarray quantitation platform, and demonstrates that clinical performance is based on the targeted cfDNA analysis method rather than the quantitation method, as the performance using microarray is comparable with performance from previous NGS studies.

Global perspectives on clinical adoption of NIPT

OBJECTIVE

The goals of this study were to assess global trends in clinical implementation of noninvasive prenatal testing (NIPT), as commercial tests are marketed increasingly worldwide, and to identify potential challenges for current or future use.

METHODS

We surveyed clinicians from 46 countries about the availability of NIPT, their experiences with using NIPT, and their views on clinical, ethical, and legal issues affecting implementation in their countries.

RESULTS

Forty-nine respondents from 28 countries completed the survey. The majority reported that NIPT is available in their country (n = 43) and that they offer NIPT in their current practice (n = 38). Eighteen respondents from 14 countries reported that there are plans to introduce NIPT into routine prenatal care in their country. Test prices varied widely, ranging from $350 to $2900, and several respondents observed that high test prices limited or restricted widespread use of NIPT. Responses varied both across and within countries regarding who is offered NIPT and what the overall screening protocol should be.

CONCLUSION

This study provides a snapshot of current use and experiences with NIPT globally. It also highlights differences in service provision that exists both across and within countries, emphasizing the need for developing national and international implementation guidelines for NIPT.

The type of feto-placental aneuploidy detected by cfDNA testing may influence the choice of confirmatory diagnostic procedure

OBJECTIVES

Cell-free DNA (cfDNA) screening can provide false positive/negative results because the fetal fraction originates primarily from trophoblast. Consequently, invasive diagnostic testing is recommended to confirm a high-risk result. Currently, there is debate about the most appropriate invasive method. We sought to estimate the frequency in which a chorionic villus sampling (CVS) performed after a high-risk cfDNA result would require a follow-up amniocentesis due to placental mosaicism.

METHODS

Analyses of the frequencies of the different types of mosaicism involving cytotrophoblasts, for trisomies 21 (T21), 18 (T18), 13 (T13) and monosomy X (MX) among 52,673 CVS karyotypes obtained from cytotrophoblast, mesenchyme and confirmatory amniocentesis.

RESULTS

After a high-risk cfDNA result for T21, 18, 13 and MX, the likelihood of finding CVS mosaicism and need for amniocentesis is, respectively, 2%, 4%, 22% and 59%. When mosaicism is detected by CVS, the likelihood of fetal confirmation by amniocentesis is, respectively, 44%, 14%, 4% and 26%.

CONCLUSIONS

In cases of high-risk cfDNA results for T21/T18, CVS (combining cytotrophoblast and mesenchyme analysis) can be considered, but with the caveat of 2-4% risk of an inconclusive result requiring further testing. In high-risk results for MX/T13, amniocentesis would appear to be the most appropriate follow-up diagnostic test, especially in the absence of sonographic findings.

Advantages and Disadvantages of Different Implementation Strategies of Non-Invasive Prenatal Testing in Down Syndrome Screening Programmes

BACKGROUND

Implementation of non-invasive prenatal testing (NIPT) in Down syndrome screening programmes requires health policy decisions about its combination with other tests and its timing in pregnancy.

AIM

Our aim was to aid health policy decision makers by conducting a quantitative analysis of different NIPT implementation strategies.

METHODS

Decision trees were created to illustrate all plausible alternatives in a theoretical cohort of 100,000 pregnant women in five screening programmes: classical screening by the first-trimester combined test (FCT), pre-selection of high-risk women prior to NIPT by the FCT, NIPT as the first screening test at 10 weeks and at 13 weeks, and the simultaneous conductance of NIPT and the FCT.

RESULTS

Pre-selection by FCT prior to NIPT reduces the number of amniocenteses to a minimum because of a reduction of false-positive NIPT results. If NIPT is the first screening test, it detects almost all fetal Down syndrome cases. NIPT at 10 weeks reassures women early in pregnancy, while NIPT at 13 weeks prevents unnecessary tests due to spontaneous miscarriages and allows for immediate confirmation by amniocentesis.

CONCLUSION

Every implementation strategy has its advantages and disadvantages. The most favourable implementation strategy may be NIPT as the first screening test at 13 weeks, offering the most accurate screening test for Down syndrome, when the risk for spontaneous miscarriage has declined remarkably and timely confirmation by amniocentesis can be performed.

Facial markers in second- and third-trimester fetuses with trisomy 18 or 13, triploidy or Turner syndrome

OBJECTIVE

To examine the effectiveness of nasal bone (NB) evaluation (including NB length (NBL)), prenasal thickness (PT) measurement, the PT:NBL ratio and the prefrontal space ratio (PFSR) in the identification of fetuses with trisomy 18 or 13, triploidy or Turner syndrome.

METHODS

This was a retrospective study using stored midsagittal two-dimensional images of the facial profile of fetuses with trisomy 18 or 13, triploidy or Turner syndrome in the second and third trimesters. For images of acceptable quality, measurements were obtained of NBL (where NB was present), PT, the PT:NBL ratio and PFSR, and these measurements were compared with previously published normal ranges.

RESULTS

The search of databases identified 189 fetuses that met the study criteria: 132 (69.8%) with trisomy 18, 40 (21.2%) with trisomy 13, 10 (5.3%) with triploidy and seven (3.7%) with Turner syndrome. The NB was either absent or its measurement was below the 5(th) centile in 67 (50.8%), 20 (50.0%), five (50.0%) and two (28.6%) of the fetuses with trisomy 18, trisomy 13, triploidy and Turner syndrome, respectively. The PT measurement was above the 95(th) centile in 24 (18.2%), six (15.0%), one (10.0%) and one (14.3%) of the affected fetuses, respectively. The PFSR was abnormal in 72 (54.5%), 29 (72.5%), seven (70%) and four (57.1%) of the cases and the PT:NBL ratio was above the 95(th) centile or the nasal bone was absent in 72 (54.5%), 20 (50.0%), six (60.0%) and four (57.1%) cases, respectively.

CONCLUSION

Although each of the facial markers considered provides some useful information in screening for trisomy 18, trisomy 13, triploidy and Turner syndrome, the performance of none of the markers appears to be as good as that in screening for trisomy 21.

Population-based trends in prenatal screening and diagnosis for aneuploidy: a retrospective analysis of 38 years of state-wide data

OBJECTIVE

To analyse population-based trends over the entire history of prenatal testing for aneuploidy.

DESIGN

Retrospective analysis of state-wide data sets.

SETTING

Australian state of Victoria with ~70 000 annual births.

POPULATION

All pregnant women undergoing invasive prenatal testing at <25 weeks' gestation from 1976 to 2013.

METHODS

Analysis of three state-wide data sets: (1) Prenatal diagnosis data set of 119 404 amniocenteses and chorionic villus samplings from 1976 to 2013; (2) central serum screening laboratory data set from 1996 to 2013; (3) government birth statistics from 1976 to 2013.

MAIN OUTCOME MEASURES

Annual numbers and uptake rates of invasive prenatal tests and serum screening, indications for invasive prenatal testing, prenatal diagnoses of aneuploidy, diagnostic yield of invasive tests.

RESULTS

Annual numbers of invasive prenatal tests climbed steadily from 1976, then declined from 2000. In 2013, the number of invasive prenatal tests was the lowest in 25 years, while the number of trisomy 21 diagnoses was the highest ever recorded. Annual uptake of serum screening climbed from 1.6 to 83% over 1996-2013. Results from 2013 showed a high diagnostic yield (15.8%) for a low rate of invasive testing (3.4% of births). Over four decades, the number of invasive procedures performed for each diagnosis of major chromosome abnormality declined from 100 to six.

CONCLUSIONS

This study demonstrates historic reductions in the proportion of women undergoing invasive testing and dramatic improvements in diagnostic yield. Monitoring the impact of new prenatal technologies on this progress remains an important research priority.

TWEETABLE ABSTRACT

Invasive prenatal testing has reached historic lows due to dramatic improvements in Down syndrome screening.

Increased Umbilical Artery Pulsatility Index in Third-Trimester Fetuses with Trisomy 21

Objective: To examine the umbilical arterial Doppler flow patterns in late third-trimester fetuses with trisomy 21. Methods: This is a retrospective study on fetuses with trisomy 21 that were evaluated after 33 weeks' gestation at the Department of Obstetrics and Gynaecology of the University of Tuebingen, Germany. The umbilical and the middle cerebral artery (UA and ACM) pulsatility index (PI) measurements and the abdominal circumference were transformed into z-values. Results: Forty-two fetuses met the study criteria. The mean gestational age at the time of the first and the second visit was 35.0 and 36.6 weeks, respectively. The mean UA PI was 1.31 and 1.38, which corresponds to z-values of 2.20 and 2.70. In 24 (57.1%) cases, both PI measurements were above the 95th centile. A linear regression analysis demonstrated that the mean of both UA PI was not dependent on the abdominal circumference or on any other examined maternal and pregnancy characteristics. The mean ACM PI at the first and the second visit was 1.62 and 1.48, respectively, corresponding to mean z-values of -0.59 and -0.75, and in none of the cases was it below the 5th centile. Conclusion: In half of the third-trimester fetuses with trisomy 21, the resistance in the UA is increased - even in the absence of placental insufficiency.

#36: Prenatal aneuploidy screening using cell-free DNA

Recent advances in technology have created exciting opportunities to expand and improve genetic testing options that are available to women during pregnancy. However, the novelty and complexity of these technologies, combined with the commercial interest to implement these tests rapidly into routine clinical care, have created challenges for physicians and patients and potentially will lead to misunderstanding, misuse, and unintended consequences. The purpose of this document was to aid clinicians in their day-to-day practice of counseling patients regarding prenatal aneuploidy testing options with cell-free DNA screening, which includes how it compares to current testing methods, potential benefits and harms, and its limitations and caveats.

Evaluating first trimester maternal serum screening combinations for Down syndrome suitable for use with reflexive secondary screening via sequencing of cell free DNA: high detection with low rates of invasive procedures

OBJECTIVES

Examine primary Down syndrome screening using combinations of first trimester serum markers, with and without sequencing of cell free DNA as a secondary reflexive test.

METHODS

Samples from 40 Down syndrome cases were matched with five control samples and tested for PAPP-A, free β, AFP, inhibin-A and PlGF. Results were converted to weight-adjusted multiples of the median (MoM) and population parameters computed. Monte Carlo simulation modeled Down syndrome detection and false positive rates for various marker combinations. After reflexive DNA testing, the revised detection and false positive rates were also computed.

RESULTS

At a primary false positive rate of 20%, the baseline combination (maternal age, PAPP-A and free β) detected 86.9%. Adding AFP or PlGF increased detection to 89.8% and 89.5%, respectively. Adding AFP and PlGF, AFP and inhibin-A, or all three markers, detected 93.7%, 94.1% and 95.5%, respectively. Modeling reflexive cf DNA testing results in little loss in detection (1%), but false positive rates fall to 0.2%.

CONCLUSION

First trimester reflexive testing does not require nuchal translucency measurements, and has high detection and very low rates of invasive procedures. However, timing of DNA sample collection and the costs of sample collection and DNA testing need to be considered before implementation.