Diagnostic accuracy of noninvasive fetal Rh genotyping from maternal blood--a meta-analysis

RHD exon 5, 7 and 10 targeted non-invasive prenatal screening of fetal Rhesus-D (RhD) in selected RhD negative pregnant women in Ethiopia

Background

A majority of non-invasive prenatal screening studies determining fetal RhD status have been tested on Caucasian and Asian populations, but limited or no studies have been conducted on the Ethiopian population. In the current study, we carried non-invasive prenatal screening of fetal RHD genotype in selected RhD negative Ethiopian pregnant women.

Methods

Cell-free DNA was extracted from the plasma samples of 117 RhD pregnant women between 9 and 38 weeks of gestation. Fetal RHD genotypes were detected by targeting exons 5, 7 and 10 of the RHD gene by using real-time PCR assay. RHD genotypic results were confirmed by neonatal cord blood serology.

Results

Fetal RHD genotyping was conclusive in all 117 subjects. RHD genotype was correctly predicted in 115 of 117 cases, thus the test yielded 98.3% accuracy (95%CI: 97.3–99.1%). Among 115 cases, 105 were genotyped as RHD positive and 12 were genotyped as RHD negative. The sensitivity and specificity of the test were 99.1% (95% CI: 94.8–99.9%) and 91.7% (95%CI: 61.5–99.7%) respectively. The negative and positive predictive values were 99.9% (95%CI: 99.2–99.9%) and 54.0% (95% CI: 15.2–88.4%) respectively. SRY genotyping results were in complete concordance with fetal sex.

Conclusion

Multi exon targeted non-invasive prenatal screening test for fetal RhD determination exhibited high accuracy and sensitivity. A confirmatory study with a bigger size of study subjects is warranted before enabling clinical implementation.

Non-Invasive Prenatal Fetal Blood Group Genotype and Its Application in the Management of Hemolytic Disease of Fetus and Newborn: Systematic Review and Meta-Analysis

Hemolytic disease of fetus and newborn (HDFN) imposes great healthcare burden being associated with maternal alloimmunization against parental-inherited fetal red blood cell antigens causing fetal anemia or death. Noninvasive prenatal analysis (NIPT) provides safe fetal RHD genotyping for early identification of risk pregnancies and proper management guidance. We aimed to conduct systematic review and meta-analysis on NIPT's beneficial application, in conjunction with quantitative maternal alloantibody analysis, for early diagnosis of pregnancies at risk. Search for relevant articles was done in; PubMed/Medline, Scopus, and Ovid (January 2006April 2020), including only English-written articles reporting reference tests and accuracy data. Nineteen eligible studies were critically appraised. NIPT was estimated highly sensitive/specific for fetal RHD genotyping beyond 11-week gestation. Amplifications from ≥2 exons are optimum to increase accuracy. NIPT permits cost-effectiveness, precious resources sparing, and low emotional stress. Knowledge of parental ethnicity is important for correct NIPT result interpretations and quantitative screening. Cut-off titer ≥8-up-to-32 is relevant for anti-D alloantibodies, while, lower titer is for anti-K. Alloimmunization is influenced by maternal RHD status, gravida status, and history of adverse obstetrics. In conclusion, NIPT allows evidence-based provision of routine anti-D immunoprophylaxis and estimates potential fetal risks for guiding further interventions. Future large-scale studies investigating NIPT's non-RHD genotyping within different ethnic groups and in presence of clinically significant alloantibodies are needed.

Non-invasive prenatal testing for management of haemolytic disease of the fetus and newborn induced by maternal alloimmunisation

Anti-D immunoglobulin prophylaxis reduces the risk of RhD negative women becoming alloimmunised to the RhD antigen and is a major preventative strategy in reducing the burden of haemolytic disease of the fetus and newborn (HDFN). HDFN also arises from other maternal red cell antibodies, with the most clinically significant, after anti-D, being anti-K, anti-c and anti-E. Among the 39 human blood group systems advanced genomic technologies are still revealing novel or rare antigens involved in maternal alloimmunisation. Where clinically significant maternal antibodies are detected in pregnancy, non-invasive prenatal testing (NIPT) of cell-free fetal DNA provides a safe way to assess the fetal blood group antigen status. This provides information as to the risk for HDFN and thus guides management strategies. In many countries, NIPT fetal RHD genotyping as a diagnostic test using real-time PCR has already been integrated into routine clinical care for the management of women with allo-anti-D to assess the risk for HDFN. In addition, screening programs have been established to provide antenatal assessment of the fetal RHD genotype in non-alloimmunised RhD negative pregnant women to target anti-D prophylaxis to those predicted to be carrying an RhD positive baby. Both diagnostic and screening assays exhibit high accuracy (over 99 %). NIPT fetal genotyping for atypical (other than RhD) blood group antigens presents more challenges as most arise from a single nucleotide variant. Recent studies show potential for genomic and digital technologies to provide a personalised medicine approach with NIPT to assess fetal blood group status for women with other (non-D) red cell antibodies to manage the risk for HDFN.

Impact of red blood cell alloimmunization on fetal and neonatal outcomes: A single center cohort study

BACKGROUND

Alloimmunization can impact both the fetus and neonate.

STUDY OBJECTIVES

(a) calculate the incidence of clinically significant RBC isoimmunization during pregnancy, (b) review maternal management and neonatal outcomes, (c) assess the value of prenatal and postnatal serological testing in predicting neonatal outcomes.

STUDY DESIGN AND METHODS

A retrospective audit of consecutive alloimmunized pregnancies was conducted. Data collected included demographics, clinical outcomes, and laboratory results. Outcomes included: incidence of alloimmunization; outcomes for neonates with and without the cognate antigen; and sensitivity and specificity of antibody titration testing in predicting hemolytic disease of the fetus and newborn (HDFN).

RESULTS

Over 6 years, 128 pregnant women (0.4%) were alloimmunized with 162 alloantibodies; anti-E was the most common alloantibody (51/162; 31%). Intrauterine transfusions (IUTs) were employed in 2 (3%) of 71 mothers of cognate antigen positive (CoAg+) neonates. Of 74 CoAg+ neonates, 58% required observation alone, 23% intensive phototherapy, 9% top up transfusion, and 3% exchange transfusion; no fetal or neonatal deaths occurred. HDFN was diagnosed in 28% (21/74) of neonates; anti-D was the most common cause. The sensitivity and specificity of the critical gel titer >32 in predicting HDFN were 76% and 75%, respectively (negative predictive value 95%; positive predictive value 36%). The sensitivity and specificity of a positive direct antiglobulin test (DAT) in predicting HDFN were 90% and 58%, respectively (NPV 97%; PPV 29%).

CONCLUSION

Morbidity and mortality related to HDFN was low; most alloimmunized pregnancies needed minimal intervention. Titers of >32 by gel warrant additional monitoring during pregnancy.

Non-invasive prenatal rhesus D genotyping using cell-free foetal DNA

Background & objectives:

Non-invasive prenatal diagnosis (NIPD) of rhesus D (RHD) genotype using cell-free foetal DNA is extensively used in many developed countries. Studies on NIPD from India are scarce. The aim of the present study was to evaluate the performance of non-invasive foetal RHD genotyping by targeting exon 10 of the RHD gene using cell-free DNA.

Methods:

DNA was extracted from the maternal plasma of alloimmunized and non-alloimmunized women between 7 and 34 wk of gestation. RHD sequence was determined by quantitative real time polymerase chain reaction (PCR). Results were compared with RhD phenotype obtained from cord blood samples of neonates.

Results:

A total of 135 samples from RhD-negative pregnant women were collected. The foetal RHD status was conclusive in all 135 (100%) cases. The highest number of cases reported for RHD genotyping were from Punjab (38.5%) followed by Haryana (24.4%), Himachal Pradesh (17.0%) and Chandigarh Union Territory (13.3%). The non-invasive test correctly predicted the foetal RhD phenotype in 133 of 135 cases, making the accuracy of the test as 98.51 per cent [95% confidence interval (CI): 97.90-99.50%]. The overall sensitivity and specificity of the test were 99.18 per cent (95% CI: 95.52-99.98%) and 92.31 per cent (95% CI: 63.97-99.81%), respectively, with negative and positive predictive values of 99.80 per cent (95% CI: 94.85-99.87%) and 96.31 per cent (95% CI: 62.87-98.84%), respectively.

Interpretation & conclusions:

Non-invasive foetal RHD determination by single-exon quantitative PCR exhibited high accuracy and could be used in routine clinical practice after confirmatory studies are done.

High-throughput non-invasive prenatal testing for fetal rhesus D status in RhD-negative women not known to be sensitised to the RhD antigen: a systematic review and economic evaluation

BACKGROUND

High-throughput non-invasive prenatal testing (NIPT) for fetal rhesus (D antigen) (RhD) status could avoid unnecessary treatment with routine anti-D immunoglobulin for RhD-negative women carrying a RhD-negative fetus, although this may lead to an increased risk of RhD sensitisations.

OBJECTIVES

To systematically review the evidence on the diagnostic accuracy, clinical effectiveness and implementation of high-throughput NIPT and to develop a cost-effectiveness model.

METHODS

We searched MEDLINE and other databases, from inception to February 2016, for studies of high-throughput NIPT free-cell fetal deoxyribonucleic acid (DNA) tests of maternal plasma to determine fetal RhD status in RhD-negative pregnant women who were not known to be sensitised to the RhD antigen. Study quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) and A Cochrane Risk of Bias Assessment Tool: for Non-Randomised Studies of Interventions (ACROBAT-NRSI). Summary estimates of false-positive rates (FPRs) and false-negative rates (FNRs) were calculated using bivariate models. Clinical effectiveness evidence was used to conduct a simulation study. We developed a de novo probabilistic decision tree-based cohort model that considered four alternative ways in which the results of NIPT could guide the use of anti-D immunoglobulin antenatally and post partum. Sensitivity analyses (SAs) were conducted to address key uncertainties and model assumptions.

RESULTS

Eight studies were included in the diagnostic accuracy review, seven studies were included in the clinical effectiveness review and 12 studies were included in the review of implementation. Meta-analyses included women mostly at or post 11 weeks' gestation. The pooled FNR (women at risk of sensitisation) was 0.34% [95% confidence interval (CI) 0.15% to 0.76%] and the pooled FPR (women needlessly receiving anti-D) was 3.86% (95% CI 2.54% to 5.82%). SAs did not materially alter the overall results. Data on clinical outcomes, including sensitisation rates, were limited. Our simulation suggests that NIPT could substantially reduce unnecessary use of antenatal anti-D with only a small increase in the risk of sensitisation. All large implementation studies suggested that large-scale implementation of high-throughput NIPT was feasible. Seven cost-effectiveness studies were included in the review, which found that the potential for the use of NIPT to produce cost savings was dependent on the cost of the test. Our de novo model suggested that high-throughput NIPT is likely to be cost saving compared with the current practice of providing routine antenatal anti-D prophylaxis to all women who are RhD negative. The extent of the cost saving appeared to be sufficient to outweigh the small increase in sensitisations. However, the magnitude of the cost saving is highly sensitive to the cost of NIPT itself.

LIMITATIONS

There was very limited evidence relating to the clinical effectiveness of high-throughput NIPT, with no evidence on potential adverse effects. The generalisability of the findings to non-white women and multiple pregnancies is unclear.

CONCLUSIONS

High-throughput NIPT is sufficiently accurate to detect fetal RhD status in RhD-negative women from 11 weeks' gestation and would considerably reduce unnecessary treatment with routine anti-D immunoglobulin, potentially resulting in cost savings of between £485,000 and £671,000 per 100,000 pregnancies if the cost of implementing NIPT is in line with that reflected in this evaluation.

FUTURE WORK

Further research on the diagnostic accuracy of NIPT in non-white women is needed.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42015029497.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Prenatal non-invasive foetal RHD genotyping: diagnostic accuracy of a test as a guide for appropriate administration of antenatal anti-D immunoprophylaxis

BACKGROUND

Foetal RHD genotyping can be predicted by real-time polymerase chain reaction (qPCR) using cell-free foetal DNA extracted from maternal plasma. The object of this study was to determine the diagnostic accuracy and feasibility of non-invasive RHD foetal genotyping, using a commercial multiple-exon assay, as a guide to appropriate administration of targeted antenatal immunoprophylaxis.

MATERIAL AND METHODS

Cell-free foetal DNA was extracted from plasma of RhD-negative women between 11-30 weeks of pregnancy. The foetal RHD genotype was determined non-invasively by qPCR amplification of exons 5, 7 and 10 of the RHD gene using the Free DNA Fetal Kit^® RhD. Results were compared with serological RhD cord blood typing at birth. The analysis of diagnostic accuracy was restricted to the period (24-28⁺⁶ weeks) during which foetal genotyping is usually performed for targeted antenatal immunoprophylaxis.

RESULTS

RHD foetal genotyping was performed on 367 plasma samples (24-28⁺⁶ weeks). Neonatal RhD phenotype results were available for 284 pregnancies. Foetal RHD status was inconclusive in 9/284 (3.2%) samples, including four cases with RhD maternal variants. Two false-positive results were registered. The sensitivity was 100% and the specificity was 97.5% (95% CI: 94.0-100). The diagnostic accuracy was 99.3% (95% CI: 98.3-100), decreasing to 96.1% (95% CI: 93.9-98.4) when the inconclusive results were included. The negative and positive predictive values were 100% (95% CI: 100-100) and 99.0% (95% CI: 97.6-100), respectively. There was one false-negative result in a sample collected at 18 weeks. After inclusion of samples at early gestational age (<23⁺⁶ week), sensitivity and accuracy were 99.6% (95% CI: 98.7-100) and 95.5% (95% CI: 93.3-97.8), respectively.

DISCUSSION

This study demonstrates that foetal RHD detection on maternal plasma using a commercial multiple-exon assay is a reliable and accurate tool to predict foetal RhD phenotype. It can be a safe guide for the appropriate administration of targeted prenatal immunoprophylaxis.

The Determination of Fetal RhD Status from Maternal Blood in Serbia

The aim of this research was to demonstrate: The specificity, sensitivity, the positive and negative prediction value of the PCR method in the detection of the fetal RhD status from maternal blood in various weeks of gestation. Which was the earliest gestational week, when is possible to get a reliable result? How did the presence of RhD antibodies in sensitized mothers affect the results? This was a prospective clinical study within a multidisciplinary project approved by the Ministry of Science of the Republic of Serbia, 2011. The study was approved by the Ethics Committee of the Medical Faculty in Belgrade. Ninety six RhD negative patients had participated in the study, with written consent. The sensitivity of the determination of the RhD status of the fetus from the mother's blood after the 7th GW in our sample was 98.6%, with a specificity of 92%. The positive predictive value of the test was 97% and the negative predictive value was 95.6%. False positive results were detected in 2.6% of cases and 4.5% of cases were false negative. This is a reliable test which should be used in monitoring of pregnancies of RhD negative mothers.

A descriptive single-centre experience of the management and outcome of maternal alloantibodies in pregnancy

BACKGROUND

Haemolytic disease of the fetus and newborn (HDFN) occurs when maternal IgG alloantibodies to fetal red blood cell antigens cross the placenta, causing haemolysis in the fetus and/or neonate. After delivery, the main concern is hyperbilirubinaemia, which can cause neurological damage.

OBJECTIVES

To summarise our current management and outcome data to inform health-care professionals counselling women whose pregnancies are at risk of HDFN and to compare these data with relevant studies.

METHODS

This is a retrospective descriptive study of all high-risk pregnancies at risk of HDFN at Guy's and St. Thomas' NHS Foundation Trust (GSTFT) Maternity Unit over a 7-year period. We defined high-risk pregnancies as those in whom anti-D, anti-c, anti-K or high (>32 or doubling strength) titres of all other antibodies were identified.

RESULTS

A total of 130 pregnancies in 112 women were followed up. A single alloantibody was found in 93 pregnancies (71.5%) and multiple alloantibodies in 37 pregnancies (28.5%). Anti-D was most commonly encountered (n = 48, 36.9%), followed by anti-c (n = 31, 23.8%) and anti-E (n = 15, 11.5%). In 65 of 130 pregnancies (50%), antibody concentrations triggered scans to screen for fetal anaemia. Of 130 pregnancies, 6 (4.6%) required intrauterine transfusions, and 31 of 130 (26%) neonates required post-natal intervention. Overall, morbidity was 0.1% and mortality 0.002%.

CONCLUSIONS

This study demonstrates that morbidity and mortality caused by HDFN is minimal. These results are reassuring for women at risk of HDFN as even severely affected cases are successfully managed in most instances. Further studies are needed to identify predictors of disease severity.

Diagnostic accuracy of fetal rhesus D genotyping using cell-free fetal DNA during the first trimester of pregnancy

BACKGROUND

Rhesus D genotyping with cell-free fetal DNA currently is used throughout the world. Although this technique has spread rapidly, its optimal use is still a matter of debate. This screening test has been introduced mainly for the treatment of RhD-negative pregnant women during the third trimester of pregnancy, thereby avoiding systematic anti-D prophylaxis, yet such a strategy has proved cost-ineffective. Publications reporting on fetal RHD genotyping with cell-free DNA in maternal plasma, specifically during the first trimester of pregnancy, are scarce in the scientific literature.

OBJECTIVE

This study sought to assess the performance of noninvasive fetal Rhesus D genotyping in the first trimester of pregnancy with a single-exon real-time polymerase chain reaction assay.

STUDY DESIGN

This was a retrospective observational multicenter study. Cell-free fetal DNA was extracted from maternal blood of both nonimmunized and immunized women at 10-14 weeks of gestation. RHD sequence was determined by quantitative polymerase chain reaction, with amplification of exon 10. Results were compared with RhD phenotype data that were obtained by cord blood sampling of neonates.

RESULTS

In total, 416 serum samples from RhD-negative pregnant women were collected during the first trimester of pregnancy. The test's overall sensitivity and specificity were 100% (95% confidence interval, 96.9-100.0) and 95.2% (95% confidence interval, 90.5-97.6), respectively. The negative and positive predictive values were 99.8% (95% confidence interval, 94.9-100.0) and 97.1% (95% confidence interval, 94.2-98.6), respectively. Fetal RHD status was inconclusive in 9 cases (2.2%).

CONCLUSION

Noninvasive fetal RHD determination by single-exon quantitative polymerase chain reaction during the first trimester of pregnancy exhibits high accuracy.

Recent advances in prenatal genetic screening and testing

The introduction of new technologies has dramatically changed the current practice of prenatal screening and testing for genetic abnormalities in the fetus. Expanded carrier screening panels and non-invasive cell-free fetal DNA-based screening for aneuploidy and single-gene disorders, and more recently for subchromosomal abnormalities, have been introduced into prenatal care. More recently introduced technologies such as chromosomal microarray analysis and whole-exome sequencing can diagnose more genetic conditions on samples obtained through amniocentesis or chorionic villus sampling, including many disorders that cannot be screened for non-invasively. All of these options have benefits and limitations, and genetic counseling has become increasingly complex for providers who are responsible for guiding patients in their decisions about screening and testing before and during pregnancy.

Determination of Fetal RHD Genotype Including the RHD Pseudogene in Maternal Plasma

OBJECTIVE

To examine the accuracy of fetal RHD genotype and RHD pseudogene determination in a multiethnical population.

METHODS

Prospective study involving D-negative pregnant women. Cell-free DNA was extracted from 1 ml of maternal plasma by an automated system (MagNA Pure Compact, Roche) and real-time PCR was performed in triplicate targeting the RHD gene exons 5 and 7. Inconclusive samples underwent RHD pseudogene testing by real-time PCR analysis employing novel primers and probe.

RESULTS

A positive result was observed in 128/185 (69.2%) samples and negative in 50 (27.0%). Umbilical cord blood phenotype confirmed all cases with a positive or negative PCR result. Seven (3.8%) cases were found inconclusive (exon 7 amplification only) and RHD pseudogene testing with both conventional and real-time PCR demonstrated a positive result in five of them, while two samples were also RHD pseudogene negative.

CONCLUSION

Real-time PCR targeting RHD exons 5 and 7 simultaneously in maternal plasma is an accurate method for the diagnosis of fetal D genotype in our population. The RHD pseudogene real-time PCR assay is feasible and is particularly useful in populations with a high prevalence of this allele.

Hemolytic disease of the fetus and newborn in the molecular era

Maternal-fetal red cell antigen incompatibility can lead to alloimmunization, maternal immunoglobulin transplacental transfer, and hemolytic disease of the fetus and newborn (HDFN). The use of routine antenatal anti-D prophylaxis (RAADP) has sharply decreased the incidence of and mortality from HDFN due to RhD allosensitization. The ability to identify pregnancies/fetuses at risk of HDFN has significantly improved due to paternal molecular RHD zygosity testing, and non-invasive fetal molecular diagnostics for detecting putative antigen(s) (notably RhD) in fetuses utilizing cff-DNA in maternal plasma. Fetal RHD genotyping using cff-DNA has become increasingly accurate for fetal RHD detection, prompting some countries to implement targeted RAADP through mass screening programs of RhD-negative pregnant women. Along with middle cerebral artery Doppler ultrasonography for predicting fetal anemia, non-invasive fetal molecular diagnostics have greatly decreased the need for invasive diagnostic procedures in pregnancies at risk for severe HDFN. This review highlights these molecular advancements in HDFN-related prenatal diagnostics.

The Glass Slide Extraction System Snap Card Improves Non-Invasive Prenatal Genotyping in Pregnancies with Antibodies

BACKGROUND

Determination of fetal blood groups in maternal plasma samples critically depends on adequate pre-analytical steps for optimal amplification of fetal DNA. We compared the extraction of cell-free DNA by binding on a glass surface (BCSI SNAP™ Card) with an automated system based on bead technology (MagnaPure compact™).

METHODS

Maternal blood samples from 281 pregnancies (7th-39th week of gestation) with known antibodies were evaluated in this study. Both the SNAP card and the MagnaPure method were applied to isolate DNA in order to directly compare the amplification in a single base extension assay and/or real-time PCR.

RESULTS

The mean concentration of total DNA obtained by the SNAP card (33.8 ng/µl) exceeded more than twofold that of MagnaPure extraction (15.7 ng/µl). SNAP card-extracted samples allowed to detect 3.7 single nucleotide polymorphisms (SNPs) versus 2.5 SNPs in MagnaPure extracts to control for traces of fetal DNA. This difference is highest for samples from 7th-13th week of gestation.

CONCLUSION

The SNAP card system improves DNA extraction efficacy for prenatal diagnosis in maternal blood samples and provides an at least eightfold higher total amount of DNA for the ensuing analysis. Its advantage is most evident for samples from early stages of pregnancy and thus especially valuable for pregnancies with antibodies.

Quantification and Application of Potential Epigenetic Markers in Maternal Plasma of Pregnancies with Hypertensive Disorders

The aim of this study was to evaluate quantitative aberrations of novel fetal-specific epigenetic markers in maternal plasma of pregnancies with hypertensive disorders. We compared the concentrations of DSCR3, RASSF1A, and SRY as cell-free fetal DNA markers in 188 normal pregnancies, 16 pregnancies with early-onset preeclampsia (EO-PE), 47 pregnancies with late-onset preeclampsia (LO-PE), and 29 pregnancies with gestational hypertension (GH). The concentrations of all markers were significantly correlated with gestational age (p < 0.001 for all). Strong positive correlations were also observed between DSCR3 and SRY (r = 0.471, p < 0.001), as well as between RASSF1A and SRY (r = 0.326, p = 0.015) and between DSCR3 and RASSF1A (r = 0.673, p < 0.001). The concentrations of DSCR3 and RASSF1A in the EO-PE were significantly higher at 24–32 weeks and onwards (p < 0.05 for both). In the LO-PE, DSCR3 and RASSF1A concentrations were significantly higher only at 33–41 weeks compared with the controls. The concentrations of all markers in the GH group were not significantly different from those in the control group. This study is the first demonstration that DSCR3 is a novel epigenetic marker that can be an alternative to the RASSF1A for the prediction of EO-PE.

Should cell-free DNA testing be used to target antenatal rhesus immune globulin administration?

OBJECTIVE

To compare the rates of alloimmunization with the use of cell-free DNA (cfDNA) screening to target antenatal rhesus immune globulin (RhIG) prenatally, versus routine administration of RhIG in rhesus D (RhD)-negative pregnant women in a theoretic cohort using a decision-analytic model.

METHODS

A decision-analytic model compared cfDNA testing to routine antenatal RhIG administration. The primary outcome was maternal sensitization to RhD antigen. Sensitivity and specificity of cfDNA testing were assumed to be 99.8% and 95.3%, respectively. Univariate and bivariate sensitivity analyses, Monte Carlo simulation, and threshold analyses were performed.

RESULTS

In a cohort of 10,000 RhD-negative women, 22.6 sensitizations would occur with utilization of cfDNA, while 20 sensitizations would occur with routine RhIG. Only when the sensitivity of the cfDNA test reached 100%, the rate of sensitization was equal for both cfDNA and RhIG. Otherwise, routine RhIG minimized the rate of sensitization, especially given RhIG is readily available in the United States.

CONCLUSIONS

Adoption of cfDNA testing would result in a 13.0% increase in sensitization among RhD-negative women in a theoretical cohort taking into account the ethnic diversity of the United States' population.

Genome-Wide Sequencing for Prenatal Detection of Fetal Single-Gene Disorders

New sequencing methods capable of rapidly analyzing the genome at increasing resolution have transformed diagnosis of single-gene or oligogenic genetic disorders in pediatric and adult medicine. Targeted tests, consisting of disease-focused multigene panels and diagnostic exome sequencing to interrogate the sequence of the coding regions of nearly all genes, are now clinically offered when there is suspicion for an undiagnosed genetic disorder or cancer in children and adults. Implementation of diagnostic exome and genome sequencing tests on invasively and noninvasively obtained fetal DNA samples for prenatal genetic diagnosis is also being explored. We predict that they will become more widely integrated into prenatal care in the near future. Providers must prepare for the practical, ethical, and societal dilemmas that accompany the capacity to generate and analyze large amounts of genetic information about the fetus during pregnancy.

Bioinformatics analysis of circulating cell-free DNA sequencing data

The discovery of cell-free DNA molecules in plasma has opened up numerous opportunities in noninvasive diagnosis. Cell-free DNA molecules have become increasingly recognized as promising biomarkers for detection and management of many diseases. The advent of next generation sequencing has provided unprecedented opportunities to scrutinize the characteristics of cell-free DNA molecules in plasma in a genome-wide fashion and at single-base resolution. Consequently, clinical applications of circulating cell-free DNA analysis have not only revolutionized noninvasive prenatal diagnosis but also facilitated cancer detection and monitoring toward an era of blood-based personalized medicine. With the remarkably increasing throughput and lowering cost of next generation sequencing, bioinformatics analysis becomes increasingly demanding to understand the large amount of data generated by these sequencing platforms. In this Review, we highlight the major bioinformatics algorithms involved in the analysis of cell-free DNA sequencing data. Firstly, we briefly describe the biological properties of these molecules and provide an overview of the general bioinformatics approach for the analysis of cell-free DNA. Then, we discuss the specific upstream bioinformatics considerations concerning the analysis of sequencing data of circulating cell-free DNA, followed by further detailed elaboration on each key clinical situation in noninvasive prenatal diagnosis and cancer management where downstream bioinformatics analysis is heavily involved. We also discuss bioinformatics analysis as well as clinical applications of the newly developed massively parallel bisulfite sequencing of cell-free DNA. Finally, we offer our perspectives on the future development of bioinformatics in noninvasive diagnosis.

Costs and benefits of non-invasive fetal RhD determination

OBJECTIVE

Non-invasive fetal Rhesus (Rh) D genotyping, using cell-free fetal DNA (cffDNA) in the maternal blood, allows targeted antenatal anti-RhD prophylaxis in unsensitized RhD-negative pregnant women. The purpose of this study was to determine the cost and benefit of this approach as compared to routine antenatal anti-RhD prophylaxis for all unsensitized RhD-negative pregnant women, as is the current policy in the province of Alberta, Canada.

METHODS

This study was a decision analysis based on a theoretical population representing the total number of pregnancies in Alberta over a 1-year period (n = 69 286). A decision tree was created that outlined targeted prophylaxis for unsensitized RhD-negative pregnant women screened for cffDNA (targeted group) vs routine prophylaxis for all unsensitized RhD-negative pregnant women (routine group). Probabilities at each decision point and costs associated with each resource were calculated from local clinical and administrative data. Outcomes measured were cost, number of women sensitized and doses of Rh immunoglobulin (RhIG) administered.

RESULTS

The estimated cost per pregnancy for the routine group was 71.43 compared with 67.20 Canadian dollars in the targeted group. The sensitization rates per RhD-negative pregnancy were equal, at 0.0012, for the current and targeted programs. Implementing targeted antenatal anti-RhD prophylaxis would save 4072 doses (20.1%) of RhIG over a 1-year period in Alberta when compared to the current program.

CONCLUSIONS

These data support the feasibility of a targeted antenatal anti-RhD prophylaxis program, at a lower cost than that of the existing routine prophylaxis program, with no increased risk of sensitization.

Non-Invasive Prenatal RHD Genotyping Using Cell-Free Fetal DNA from Maternal Plasma: An Italian Experience

BACKGROUND

This study assessed the diagnostic accuracy of a non-invasive approach to fetal RHD genotyping using cell-free fetal DNA in maternal plasma and a combination of methodological strategies.

METHODS

Real-time PCR (qPCR) was performed on 216 RhD-negative women between weeks 10+0 and 14+6 of gestation (1st qPCR). qPCR was repeated (2nd qPCR) to increase the amount of each sample for analysis, on 95 plasma aliquots that were available from first trimester blood collection (group 1) and on 13 samples that were collected between weeks 18+0 and 25+6 of gestation (group 2). qPCR was specific for exons 5 and 7 of the RHD gene (RHD5 and RHD7). The results were interpreted according to the number of positive replicates of both exons.

RESULTS

1st qPCR: diagnostic accuracy was of 93.3%. Diagnostic accuracy increased from 90.5% (1st qPCR) to 93.7% (2nd qPCR) in group 1 and from 84.6% (1st qPCR) to 92.3% (2nd qPCR) in group 2. These increments were not statistically significant.

CONCLUSION

Our approach to RHD genotyping in early pregnancy yielded high diagnostic accuracy. Increasing the amount of DNA analyzed in each sample did not improve significantly the diagnostic accuracy of the test.

Noninvasive single-exon fetal RHD determination in a routine screening program in early pregnancy

OBJECTIVE

To develop a simple and robust assay suitable for fetal RHD screening in first-trimester pregnancy and to estimate the sensitivity and specificity of the test after its implementation in an unselected pregnant population.

METHODS

Pregnant women attending their first antenatal visit were included, and fetal RHD determination was performed for all women who typed RhD-negative by routine serology. DNA was extracted by an automated system and quantitative polymerase chain reaction was done by an assay based on exon 4. Reporting criteria were simple and strict.

RESULTS

Four thousand one hundred eighteen pregnancies, with a median gestational age of 10 weeks, were included. After 211 (5.1%) reanalyses, fetal RHD was reported positive in 2,401 (58.3%), negative in 1,552 (37.7%), and inconclusive in 165 (4.0%) based on the first sample. After a second sample in 147 of 165, only 14 remained inconclusive, all resulting from a weak or silent maternal RHD gene. Using blood group serology of the newborns as the gold standard, the false-negative rate was 55 of 2,297 (2.4%) and the false-positive rate was 15 of 1,355 (1.1%). After exclusion of samples obtained before gestational week 8, the false-negative rate was 23 of 2,073 (1.1%) and the false-positive rate was 14 of 1,218 (1.1%). Both sensitivity and specificity were close to 99% provided samples were not collected before gestational week 8. From gestational week 22, sensitivity was 100%.

CONCLUSION

Fetal RHD detection in early pregnancy using a single-exon assay in a routine clinical setting is feasible and accurate.

LEVEL OF EVIDENCE

I.

Determination of fetal rhesus d status by maternal plasma DNA analysis

In this study, we assessed the feasibility of fetal RhD genotyping by analysis of cell-free fetal DNA(cffDNA) extracted from plasma samples of Rhesus (Rh) D-negative pregnant women by using real-time polymerase chain reaction (PCR). Fetal genotyping was performed on 30 RhD-negative women between 9 and 39 weeks of gestation who were referred to us for invasive testing [amniocentesis/chorionic villi sampling (CVS)]. The fetal RHD genotype was determined based on real-time PCR method. Exons 7 and 10 of the RHD and SRY genes were targeted.

Among the pregnant women, 12 were carrying male and 17 were carrying female fetuses. Out of 29 pregnant women, 21 had RhD-positive and nine had RhD-negative fetuses. One sample (case 12, whose blood group was found to be AB Rh [+]) was excluded due to controversial results from repeated serological analyses. All prenatal results were in concordance with postnatal RhD status and fetal sex without false- positive or -negative results. Performing real-time PCR on cffDNA showed accurate, efficient and reliable results, allowing rapid and high throughput non invasive determination of fetal sex and RhD status in clinical samples.

Integration of noninvasive prenatal prediction of fetal blood group into clinical prenatal care

Incompatibility of red blood cell blood group antigens between a pregnant woman and her fetus can cause maternal immunization and, consequently, hemolytic disease of the fetus and newborn. Noninvasive prenatal testing of cell-free fetal DNA can be used to assess the risk of hemolytic disease of the fetus and newborn to fetuses of immunized women. Prediction of the fetal RhD type has been very successful and is now integrated into clinical practice to assist in the management of the pregnancies of RhD immunized women. In addition, noninvasive prediction of the fetal RhD type can be applied to guide targeted prenatal prophylaxis, thus avoiding unnecessary exposure to anti-D in pregnant women. The analytical aspect of noninvasive fetal RHD typing is very robust and accurate, and its routine utilization has demonstrated high sensitivities for fetal RHD detection. A high compliance with administering anti-D is essential for obtaining a clinical effect. Noninvasive fetal typing of RHC/c, RHE/e, and KEL may become more widely used in the future.

Targeted routine antenatal anti-D prophylaxis in the prevention of RhD immunisation--outcome of a new antenatal screening and prevention program

Objective

To estimate the incidence of RhD immunisation after implementation of first trimester non-invasive fetal RHD screening to select only RhD negative women carrying RHD positive fetuses for routine antenatal anti-D prophylaxis (RAADP).

Materials and Methods

We present a population-based prospective observational cohort study with historic controls including all maternity care centres and delivery hospitals in the Stockholm region, Sweden. All RhD negative pregnant women were screened for fetal RHD genotype in the first trimester of pregnancy. Anti-D immunoglobulin (250–300 µg) was administered intramuscularly in gestational week 28–30 to participants with RHD positive fetuses. Main outcome measure was the incidence of RhD immunisation developing during or after pregnancy.

Results

During the study period 9380 RhD negative women gave birth in Stockholm. Non-invasive fetal RHD genotyping using cell-free fetal DNA in maternal plasma was performed in 8374 pregnancies of which 5104 (61%) were RHD positive and 3270 (39%) RHD negative. In 4590 pregnancies with an RHD positive test the women received antenatal anti-D prophylaxis. The incidence of RhD immunisation in the study cohort was 0.26 percent (24/9380) (95% CI 0.15–0.36%) compared to 0.46 percent (86/18546) (95% CI 0.37 to 0.56%) in the reference cohort. The risk ratio (RR) for sensitisation was 0.55 (95% CI 0.35 to 0.87) and the risk reduction was statistically significant (p = 0.009). The absolute risk difference was 0.20 percent, corresponding to a number needed to treat (NNT) of 500.

Conclusions

Using first trimester non-invasive antenatal screening for fetal RHD to target routine antenatal anti-D prophylaxis selectively to RhD negative women with RHD positive fetuses significantly reduces the incidence of new RhD immunisation. The risk reduction is comparable to that reported in studies evaluating the outcome of non selective RAADP to all RhD negative women. The cost-effectiveness of this targeted approach remains to be studied.

Survey on the prevention and incidence of haemolytic disease of the newborn in Italy

BACKGROUND

In 2010, the Italian Society of Immunohaematology and Transfusion Medicine (SIMTI) carried out a survey of the incidence of haemolytic disease of the newborn (HDN) and the prevention of HDN caused by anti-Rh(D) in Italian Transfusion Structures (TS).

MATERIALS AND METHODS

A questionnaire divided into the following five sections was administered: (i) types of services provided and maintenance of legally required registers, (ii) immunoprophylaxis (IP), (iii) red cell typing and searches for irregular antibodies, (iv) evaluation of foetal-maternal haemorrhage (FMH), and (v) incidence of HDN in 2010. Of the 280 TS sent the questionnaire, 176 (63%) replied.

RESULTS

A HDN register was available in 55.5% of the TS (n =91). Immunoprophylaxis with a dose of anti-D IgG was given to all Rh(D) negative and Rh(D) variant puerpera with Rh(D) positive newborns: in more than 93% of cases the dose was between 1,500 IU (300 μg) and 1,250 IU (250 μg). Antenatal IP between the 25(th) and 28(th) week was proposed by 42 TS (26%). Seventy percent of the TS (n =115) did not make any evaluation of FMH. The number of births surveyed in 2010 was 203,384, the number of Rh(D) negative pregnancies was 13,569, while anti-D antibodies were present in 245 pregnancies. There were 111 cases of HDN due to anti Rh(D) incompatibility and in 40 of these, intrauterine transfusion (n =8) or exchange transfusion (n =32) was necessary. In 94 cases HDN was due to other irregular antibodies: in 4 of these cases intrauterine transfusion was needed and in 11 other recourse was made of exchange transfusion. Finally, there were 1,456 newborns with ABO HDN of whom 13 underwent exchange transfusion.

DISCUSSION

The data collected give a picture of the incidence of HDN in Italy and of the methods of managing IP and could form the basis for an update of the SIMTI recommendations on the management and prevention of this disease.

Clinical application of midtrimester non-invasive fetal RHD genotyping and identification of RHD variants in a mixed-ethnic population

OBJECTIVE

This study aims to assess the suitability of non-invasive prenatal RHD genotyping in non-immunized midtrimester pregnant women from a mixed ethnic population, to prevent unnecessary anti-D immunoglobulin prophylaxis and to identify RHD variants

METHODS

Rhesus D-negative pregnant women were offered fetal RHD genotyping at 24 gestational weeks. A total of 284 samples were tested for RHD status using multiplex rt-PCR amplification of exons 5 and 7 of the RHD gene and exons 6 and 10 in selected cases. Women carrying RHD-negative fetuses were counseled about their option to avoid routine antenatal anti-D immunoglobulin administration. Diagnostic accuracy of RHD genotyping was compared with postnatal Rhesus D serotyping.

RESULTS

A total of 184 positives (65%), 91 negatives (32%) and 7 cases (2.5%) compatibles with RHD variants were detected by RHD genotyping. No false negative results were found, and a single false positive was observed in a twin pregnancy. Genotyping was accepted when offered by 94% of women (284/302), and anti-D immunoglobulin was avoided in 95% (90/95) of RHD-negative fetuses.

CONCLUSIONS

Non-invasive routine antenatal RHD genotyping at 24 weeks of pregnancy is a highly accurate method, resulting in the avoidance of 95% of unnecessary administrations of anti-D immunoglobulin, with no false negative results.

Association of fetal-derived hypermethylated RASSF1A concentration in placenta-mediated pregnancy complications

OBJECTIVES

To assess whether fetal-derived hypermethylated RASSF1A concentrations in maternal plasma during pregnancy are altered in pregnancies associated with placental dysfunction manifested by intrauterine growth restriction (IUGR), preeclampsia (PE), or placental previa (PP) and whether this alteration can be detected in susceptible subjects before the onset of clinical disease.

METHODS

We performed a real-time quantitative polymerase chain reaction to quantify RASSF1A concentrations before and after methylation-sensitive restriction digestion in maternal plasma at 7-41 gestational weeks of normal pregnancies (n = 161), IUGR (n = 43), PE (n = 22), PP (n = 14) and non-pregnant women (n = 20).

RESULTS

A positive correlation was observed between fetal-derived hypermethylated RASSF1A concentration and gestational age for all study groups (r = 0.624, p < 0.001 for IUGR; r = 0.381, p = 0.042 for PE; r = 0.697, p < 0.001 for PP; r = 0.560, p < 0.001 for controls). The concentration of hypermethylated RASSF1A was relatively high at 7-14 gestational weeks in all patient groups. Hypermethylated RASSF1A concentration at 15-28 weeks was significantly higher in patients who subsequently developed IUGR (p = 0.002), PE (p < 0.001) or PP (p < 0.001) than in controls.

CONCLUSION

We first demonstrated increased concentration of fetal-derived hypermethylated RASSF1A sequences according to advancing gestation and before the onset of the clinical manifestation of pregnancy complications secondary to placental dysfunction, such as IUGR, PE and PP. Hypermethylated RASSF1A in maternal plasma may be useful as a potential biomarker to detect placental-mediated pregnancy complications, regardless of fetal gender and polymorphism.

Noninvasive prenatal detection and selective analysis of cell-free DNA obtained from maternal blood: evaluation for trisomy 21 and trisomy 18

OBJECTIVE

We sought to develop a novel biochemical assay and algorithm for the prenatal evaluation of risk for fetal trisomy 21 (T21) and trisomy 18 (T18) using cell-free DNA obtained from maternal blood.

STUDY DESIGN

We assayed cell-free DNA from a training set and a blinded validation set of pregnant women, comprising 250 disomy, 72 T21, and 16 T18 pregnancies. We used digital analysis of selected regions in combination with a novel algorithm, fetal-fraction optimized risk of trisomy evaluation (FORTE), to determine trisomy risk for each subject.

RESULTS

In all, 163/171 subjects in the training set passed quality control criteria. Using a Z statistic, 35/35 T21 cases and 7/7 T18 cases had Z statistic >3 and 120/121 disomic cases had Z statistic <3. FORTE produced an individualized trisomy risk score for each subject, and correctly discriminated all T21 and T18 cases from disomic cases. All 167 subjects in the blinded validation set passed quality control and FORTE performance matched that observed in the training set correctly discriminating 36/36 T21 cases and 8/8 T18 cases from 123/123 disomic cases.

CONCLUSION

Digital analysis of selected regions and FORTE enable accurate, scalable noninvasive fetal aneuploidy detection.

Cell-free fetal nucleic acid testing: a review of the technology and its applications

Cell-free fetal nucleic acids circulating in the blood of pregnant women afford the opportunity for early, noninvasive prenatal genetic testing. The predominance of admixed maternal genetic material in circulation demands innovative means for identification and analysis of cell-free fetal DNA and RNA. Techniques using polymerase chain reaction, mass spectrometry, and sequencing have been developed for the purposes of detecting fetal-specific sequences, such as paternally inherited or de novo mutations, or determining allelic balance or chromosome dosage. Clinical applications of these methods include fetal sex determination and blood group typing, which are currently available commercially although not offered routinely in the United States. Other uses of cell-free fetal DNA and RNA being explored are the detection of single-gene disorders, chromosomal abnormalities, and inheritance of parental polymorphisms across the whole fetal genome. The concentration of cell-free fetal DNA may also provide predictive capabilities for pregnancy-associated complications. The roles that cell-free fetal nucleic acid testing assume in the existing framework of prenatal screening and invasive diagnostic testing will depend on factors such as costs, clinical validity and utility, and perceived benefit-risk ratios for different applications. As cell-free fetal DNA and RNA testing continues to be developed and translated, significant ethical, legal, and social questions will arise that will need to be addressed by those with a stake in the use of this technology.

TARGET AUDIENCE

Obstetricians & Gynecologists and Family Physicians Learning Objectives: After participating in this activity, physicians should be better able to evaluate techniques and tools for analyzing cell-free fetal nucleic acids, assess clinical applications of prenatal testing, using cell-free fetal nucleic acids and barriers to implementation, and distinguish between relevant clinical features of cell-free fetal nucleic acid testing and existing prenatal genetic screening and diagnostic procedures.

Standardization non-invasive fetal RHD and SRY determination into clinical routine using a new multiplex RT-PCR assay for fetal cell-free DNA in pregnant women plasma: results in clinical benefits and cost saving

INTRODUCTION

Among negative RhD mothers it is essential to know the fetal RhD status in order to avoid the possibility of hemolytic disease of the newborn. In this regard, the detection of fetal DNA in maternal plasma might become a new diagnostic tool. In the current study, we have evaluated the standardization of a Multiplex-PCR targeted towards two exons of the RHD and one SRY gene to monitor RhD negative women. The current study addresses questions concerning feasibility and applicability of this approach into the clinical practice.

MATERIALS AND METHODS

Both single and multiplex real-time PCRs targeting RHD exons 5 and 7 and SRY were applied for the detection of fetal-specific RHD sequences and sex in maternal plasma. A large cohort of 2127 women was studied between 10 and 28 weeks of pregnancy. 134 of them were used for single TaqMan PCR studies and 1993 were evaluated using Multiplex TaqMan PCR studies. All of them were serologically typed as RhD negative according to Spanish guidelines. Single and multiplex real-time PCR results were compared with postnatal serology and sex identification.

RESULTS

There was a 100% concordance between results obtained with single and multiplex real-time PCR assays. At present, 1012 of the 1993 pregnant women studied gave birth and the results of RHD status obtained with the multiplex TaqMan PCR assay were confirmed postpartum by serological methods showing that sensitivity, specificity, and accuracy of the multiplex assay were 100, 98.6, and 99.3%, respectively. This procedure improved the speed of the assay, avoided over-treatment among RhD negative pregnant women bearing RhD negative fetus, and reduced the requirements for clinical and biological monitoring, resulting in a clinical benefit and cost saving.

CONCLUSIONS

The routine determination of fetal RHD status and SRY in maternal plasma, using multiplex real-time PCR, is feasible. The use of multiplex real-time PCR allows improving the response of the laboratory, saving time and reagent costs, opening the door to a complete automatization of the process.

Noninvasive approach for the management of hemolytic disease of the fetus

Hemolytic disease of the fetus and newborn (HDFN) is due to maternal alloantibodies directed against paternally inherited antigens on fetal red cells, and it is still a problem in affected pregnancies despite the routine use of anti-D immunoglobulin during pregnancy and shortly after delivery. The current noninvasive management of HDFN starts with the determination of fetal RhD genotype by use of cell-free fetal DNA in maternal plasma. When the fetus is antigen positive, the follow-up is performed by Doppler ultrasonography for the detection of moderate or severe anemia on the basis of an increase peak velocity of systolic blood in the middle cerebral artery. Finally, if anemia is suspected, an invasive approach is required in order to perform an intrauterine blood transfusion, which should only be attempted when the fetus needs transfusion. This approach reduces the iatrogenic conversion of mild-to-severe disease, which occurred as a result of the previous invasive management, and prevents unnecessary administration of human-derived blood products. These changes represent one of the genuine successes of fetal therapy.

Cell-free fetal nucleic acids as prenatal biomarkers

INTRODUCTION

Cell-free fetal nucleic acids in maternal plasma or serum have become important tools in the pursuance of new methods for non-invasive prenatal diagnosis, such as the determination of fetal blood groups and fetal gender. During these pioneering explorations, elevations in the concentration of these new-found biological analytes were noted in several pregnancy-related disorders, including preterm labor, pre-eclampsia and malimplantation. As these elevations appeared to occur before onset of clinical symptoms, it was proposed that such analyses might assist in screening for at-risk pregnancies. A major problem with these early studies is that they relied on the quantitation of Y-chromosome-specific gene sequences, and as such could be applied only in those cases where the fetus was male. Recent developments that might permit gender-independent analysis include epigenetic markers, as well as the analysis of cell-free placentally derived mRNA species.

AREAS COVERED

This article focuses specifically on prognostic markers, which enable at-risk pregnancies to be identified, allowing the modification of pregnancy management and in turn improvement of pregnancy outcome. The authors also provide their opinion on the progress and future challenges that lie ahead.

EXPERT OPINION

Accurate quantification of fetal nucleic acids and the specificity of these elevations for particular disorders remain controversial issues. Regarding the multifactorial etiology of some pregnancy disorders, the use of fetal nucleic acids as prenatal markers is restricted to well-defined high-risk groups.