Use of cffDNA to avoid administration of anti-D to pregnant women when the fetus is RhD-negative: implementation in the NHS

Antenatal RHD screening to guide antenatal anti-D immunoprophylaxis in non-immunized D- pregnant women

In pregnancy, D- pregnant women may be at risk of becoming immunized against D when carrying a D+ fetus, which may eventually lead to hemolytic disease of the fetus and newborn. Administrating antenatal and postnatal anti-D immunoglobulin prophylaxis decreases the risk of immunization substantially. Noninvasive fetal RHD genotyping, based on testing cell-free DNA extracted from maternal plasma, offers a reliable tool to predict the fetal RhD phenotype during pregnancy. Used as a screening program, antenatal RHD screening can guide the administration of antenatal prophylaxis in non-immunized D- pregnant women so that unnecessary prophylaxis is avoided in those women who carry a D- fetus. In Europe, antenatal RHD screening programs have been running since 2009, demonstrating high test accuracies and program feasibility. In this review, an overview is provided of current state-of-the-art antenatal RHD screening, which includes discussions on the rationale for its implementation, methodology, detection strategies, and test performance. The performance of antenatal RHD screening in a routine setting is characterized by high accuracy, with a high diagnostic sensitivity of ≥99.9 percent. The result of using antenatal RHD screening is that 97-99 percent of the women who carry a D- fetus avoid unnecessary prophylaxis. As such, this activity contributes to avoiding unnecessary treatment and saves valuable anti-D immunoglobulin, which has a shortage worldwide. The main challenges for a reliable noninvasive fetal RHD genotyping assay are low cell-free DNA levels, the genetics of the Rh blood group system, and choosing an appropriate detection strategy for an admixed population. In many parts of the world, however, the main challenge is to improve the basic care for D- pregnant women.

Validation of a non-invasive prenatal test for fetal RhD, C, c, E, K and Fya antigens

We developed and validated a next generation sequencing-(NGS) based NIPT assay using quantitative counting template (QCT) technology to detect RhD, C, c, E, K (Kell), and Fya (Duffy) fetal antigen genotypes from maternal blood samples in the ethnically diverse U.S. population. Quantitative counting template (QCT) technology is utilized to enable quantification and detection of paternally derived fetal antigen alleles in cell-free DNA with high sensitivity and specificity. In an analytical validation, fetal antigen status was determined for 1061 preclinical samples with a sensitivity of 100% (95% CI 99-100%) and specificity of 100% (95% CI 99-100%). Independent analysis of two duplicate plasma samples was conducted for 1683 clinical samples, demonstrating precision of 99.9%. Importantly, in clinical practice the no-results rate was 0% for 711 RhD-negative non-alloimmunized pregnant people and 0.1% for 769 alloimmunized pregnancies. In a clinical validation, NIPT results were 100% concordant with corresponding neonatal antigen genotype/serology for 23 RhD-negative pregnant individuals and 93 antigen evaluations in 30 alloimmunized pregnancies. Overall, this NGS-based fetal antigen NIPT assay had high performance that was comparable to invasive diagnostic assays in a validation study of a diverse U.S. population as early as 10 weeks of gestation, without the need for a sample from the biological partner. These results suggest that NGS-based fetal antigen NIPT may identify more fetuses at risk for hemolytic disease than current clinical practice, which relies on paternal genotyping and invasive diagnostics and therefore is limited by adherence rates and incorrect results due to non-paternity. Clinical adoption of NIPT for the detection of fetal antigens for both alloimmunized and RhD-negative non-alloimmunized pregnant individuals may streamline care and reduce unnecessary treatment, monitoring, and patient anxiety.

Cost-effectiveness of noninvasive fetal RhD blood group genotyping in nonalloimmunized and alloimmunized pregnancies

BACKGROUND

We sought to determine the cost-effectiveness of noninvasive fetal RhD blood group genotyping in nonalloimmunized and alloimmunized pregnancies in Canada.

STUDY DESIGN AND METHODS

We developed two probabilistic state-transition (Markov) microsimulation models to compare fetal genotyping followed by targeted management versus usual care (i.e., universal Rh immunoglobulin [RhIG] prophylaxis in nonalloimmunized RhD-negative pregnancies, or universal intensive monitoring in alloimmunized pregnancies). The reference case considered a healthcare payer perspective and a 10-year time horizon. Sensitivity analysis examined assumptions related to test cost, paternal screening, subsequent pregnancies, other alloantibodies (e.g., K, Rh c/C/E), societal perspective, and lifetime horizon.

RESULTS

Fetal genotyping in nonalloimmunized pregnancies (at per-sample test cost of C$247/US$311) was associated with a slightly higher probability of maternal alloimmunization (22 vs. 21 per 10,000) and a reduced number of RhIG injections (1.427 vs. 1.795) than usual care. It was more expensive (C$154/US$194, 95% Credible Interval [CrI]: C$139/US$175-C$169/US$213) and had little impact on QALYs (0.0007, 95%CrI: -0.01-0.01). These results were sensitive to the test cost (threshold achieved at C$88/US$111), and inclusion of paternal screening. Fetal genotyping in alloimmunized pregnancies (at test cost of C$328/US$413) was less expensive (-C$6280/US$7903, 95% CrI: -C$6325/US$7959 to -C$6229/US$7838) and more effective (0.19 QALYs, 95% CrI 0.17-0.20) than usual care. These cost savings remained robust in sensitivity analyses.

DISCUSSION

Noninvasive fetal RhD genotyping saves resources and represents good value for the management of alloimmunized pregnancies. If the cost of genotyping is substantially decreased, the targeted intervention can become a viable option for nonalloimmunized pregnancies.

Recommendation for validation and quality assurance of non-invasive prenatal testing for foetal blood groups and implications for IVD risk classification according to EU regulations

BACKGROUND AND OBJECTIVES

Non-invasive assays for predicting foetal blood group status in pregnancy serve as valuable clinical tools in the management of pregnancies at risk of detrimental consequences due to blood group antigen incompatibility. To secure clinical applicability, assays for non-invasive prenatal testing of foetal blood groups need to follow strict rules for validation and quality assurance. Here, we present a multi-national position paper with specific recommendations for validation and quality assurance for such assays and discuss their risk classification according to EU regulations.

MATERIALS AND METHODS

We reviewed the literature covering validation for in-vitro diagnostic (IVD) assays in general and for non-invasive foetal RHD genotyping in particular. Recommendations were based on the result of discussions between co-authors.

RESULTS

In relation to Annex VIII of the In-Vitro-Diagnostic Medical Device Regulation 2017/746 of the European Parliament and the Council, assays for non-invasive prenatal testing of foetal blood groups are risk class D devices. In our opinion, screening for targeted anti-D prophylaxis for non-immunized RhD negative women should be placed under risk class C. To ensure high quality of non-invasive foetal blood group assays within and beyond the European Union, we present specific recommendations for validation and quality assurance in terms of analytical detection limit, range and linearity, precision, robustness, pre-analytics and use of controls in routine testing. With respect to immunized women, different requirements for validation and IVD risk classification are discussed.

CONCLUSION

These recommendations should be followed to ensure appropriate assay performance and applicability for clinical use of both commercial and in-house assays.

The Significance of RHD Genotyping and Characteristic Analysis in Chinese RhD Variant Individuals

Background

RhD is the most important and complex blood group system because of its highly polymorphic and immunogenic nature. RhD variants can induce immune response by allogeneic transfusion, organ transplantation, and fetal immunity. The transfusion strategies are different for RhD variants formed by various alleles. Therefore, extensive investigation of the molecular mechanism underlying RhD variants is critical for preventing immune-related blood transfusion reactions and fetal immunity.

Methods

RhD variants were collected from donors and patients in Zhejiang Province, China. The phenotypes were classified using the serologic method. The full coding regions of RHD gene were analyzed using the PCR-SBT method. The multiplex ligation-dependent probe amplification (MLPA) assay was used to analyze the genotype and gene copy number. SWISS-MODLE and PyMOL software were used to analyze 3D structures of RhD caused by the variant alleles. The effect of non-synonymous substitutions was predicted using Polymorphism Phenotyping algorithm (PolyPhen-2), Sorting Intolerant From Tolerant (SIFT), and Protein Variation Effect Analyzer (PROVEAN) software.

Results

In the collected RhD variants, 28 distinct RHD variant alleles were identified, including three novel variant alleles. RH-MLPA assay is advantageous for determining the copy number of RHD gene. 3D homology modeling predicted that protein conformation was disrupted and may explain RhD epitope differential expression. A total of 14 non-synonymous mutations were determined to be detrimental to the protein structure.

Discussion

We revealed the diversity of RHD alleles present in eastern Chinese RhD variants. The bioinformatics of these variant alleles extended our knowledge of RhD variants, which was crucial for evaluating their impact to guide transfusion support and avoid immune-related blood transfusion reactions.

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.

Prenatal RHD genotyping in Croatia: preliminary results

OBJECTIVES

Croatian Institute of Transfusion Medicine (CITM) implemented non-invasive fetal RHD genotyping as a request for targeted antenatal anti-D prophylaxis. The diagnostic performance of in-house RT-PCR method for fetal RHD genotyping and preliminary results are analyzed.

MATERIALS AND METHODS

Evaluation included results of RHD genotyping for 205 RhD negative pregnant women, 12-36th week of gestation, whose samples were received in period between 2015 and 2020. QIAsymphony SP DSP Virus Midi Kit was used for cffDNA extraction on QIAsymphony SP platform (Qiagen, Germany). Fragments of RHD exons 7 and 10 and later exon 5 were RT-PCR amplified. As internal controls, amplification of SRY gene or RASSF1A fragment and β-actin genes digested with BsTUI were used.

RESULTS

We identified 70.72% (145/205) positive and 28.78% (59/205) negative fetal RHD genotypes. We had one inconclusive result (0.50%) due to the interference of maternal DNA with variant genotype RHD*09.02.00/01/*01N.01. When compared to newborns RhD phenotypes, no false negative and three false positive results (3/199, 1.50%) were observed. The test yielded 100% sensitivity and 95.08% specificity, while diagnostic accuracy was 98.48%. We were able to determine one case of fetal variant genotype RHD*04.04/*01N.01 inherited from the father. The negative and positive predictive test values were 100% and 97.86%, respectively.

CONCLUSION

Automated cffDNA extraction and RT-PCR amplification of fetal RHD exons 5,7,10 and fragments of SRY, RASSF1A genes represents highly reliable system for determining fetal RHD status which enables targeted antenatal anti-D prophylaxis. To obtain high specificity of cffDNA extraction, strict and thoroughly cleaning procedures are required.

Implementation of high-throughput non-invasive prenatal testing for fetal RHD genotype testing in England: Results of a cross-sectional survey of maternity units and expert interviews

Background

Previously, routine antenatal anti‐D prophylaxis (RAADP) was administered to all RhD‐negative mothers to reduce the risk of sensitisation in the UK's National Health Service (NHS). If the baby is RhD‐negative, RAADP is not required. In 2016, the UK National Institute for Health and Care Excellence (NICE) recommended non‐invasive prenatal testing (NIPT) for fetal RHD genotype as a cost‐effective option to guide RAADP.

Objectives

To evaluate the implementation of high‐throughput NIPT for fetal RHD genotype in maternity units in England by addressing research recommendations from the NICE. These were to reduce uncertainty around the resource use and cost of staff training, management of samples and results and record‐keeping, as well as resultant changes to antenatal or post‐partum care and performance of NIPT.

Methods

A cross‐sectional survey was developed and sent to clinicians at 39 English NHS Trusts in May 2018. Qualitative interviews with seven individuals were conducted to explore missing or contraindicatory data. Qualitative findings were supplemented with NIPT test results (April 2017 to February 2019) from English hospitals.

Results

Staff reported that training took up to 30 minutes. There were no extra costs associated with sample management or additional appointments. Extra time required for record‐keeping and management of test results was balanced later in the patient pathway. The antenatal pathway was not changed in the Trusts surveyed. The survey revealed that four post‐partum scenarios were being used within English NHS Trusts. The frequency of inconclusive NIPT results was 4.3%.

Conclusion

NIPT for fetal RHD genotype can be implemented without consuming substantial extra resources through incorporation into an existing patient pathway.

Targeted antenatal anti-D prophylaxis for RhD-negative pregnant women: a systematic review

Background

All non-sensitized Rhesus D (RhD)-negative pregnant women in Germany receive antenatal anti-D prophylaxis without knowledge of fetal RhD status. Non-invasive prenatal testing (NIPT) of cell-free fetal DNA in maternal plasma could avoid unnecessary anti-D administration. In this paper, we systematically reviewed the evidence on the benefit of NIPT for fetal RhD status in RhD-negative pregnant women.

Methods

We systematically searched several bibliographic databases, trial registries, and other sources (up to October 2019) for controlled intervention studies investigating NIPT for fetal RhD versus conventional anti-D prophylaxis. The focus was on the impact on fetal and maternal morbidity. We primarily considered direct evidence (from randomized controlled trials) or if unavailable, linked evidence (from diagnostic accuracy studies and from controlled intervention studies investigating the administration or withholding of anti-D prophylaxis). The results of diagnostic accuracy studies were pooled in bivariate meta-analyses.

Results

Neither direct evidence nor sufficient data for linked evidence were identified. Meta-analysis of data from about 60,000 participants showed high sensitivity (99.9%; 95% CI [99.5%; 100%] and specificity (99.2%; 95% CI [98.5%; 99.5%]).

Conclusions

NIPT for fetal RhD status is equivalent to conventional serologic testing using the newborn’s blood. Studies investigating patient-relevant outcomes are still lacking.

Fetal RHD detection from circulating cell-free fetal DNA in maternal plasma: validation of a diagnostic kit using automatic extraction and frozen DNA

OBJECTIVE

This study aimed to validate non-invasive RHD genotyping of cell-free fetal DNA (cff-DNA) using different DNA extraction methods and of fresh and frozen extracted cff-DNA.

BACKGROUND

Non-invasive RHD genotyping of cff-DNA predicts fetal RhD phenotype, allowing for the rational implementation of antenatal immunoprophylaxis and representing a big step forward in the management of RhD-immunised women. Validation of a diagnostic method is mandatory before its clinical application.

METHODS

RhD-negative pregnant women were recruited at different gestational ages. The cff-DNA extraction was carried out using manual and automatic methods in order to improve cff-DNA yield and optimise the extraction. Fetal RHD genotyping was performed using a commercial real-time polymerase chain reaction (PCR) kit, and the results were compared with postnatal serological RhD determination on cord blood.

RESULTS

Overall, 133 plasma samples were examined for the validation process, and a total of 423 tests were performed. No differences have been observed between the two extraction methods or between fresh or frozen cff-DNA regarding cff-DNA stability and quality parameters. There was 100% concordance between fetal RHD genotyping of cff-DNA and RhD phenotype on cord blood for both extraction methods on both fresh and frozen cff-DNA.

CONCLUSION

Our study shows the reliability of automatic and manual cff-DNA extraction methods and the possibility of freezing extracted cff-DNA when performing RHD genotyping. This result might be relevant for improving laboratory work and organisation through the development of a standardised procedure for fetal RHD genotyping on cff-DNA, laying the foundations for evidence-based use of anti-D Ig prophylaxis in RhD pregnant women.

Prevalence and obstetric outcome of women with red cell antibodies in pregnancy at the Leeds Teaching Hospitals NHS Trust, West Yorkshire, England

OBJECTIVE

The prevalence of red cell antibodies in pregnancy varies with ethnicity and geographical location, while the obstetric outcome depends on the available standard of care. Despite being the tertiary fetal medicine centre in West Yorkshire, the prevalence of red cell antibodies, and the outcome of pregnancies associated with these antibodies at the Leeds University Teaching Hospitals Trust remains unreported. This article aims to provide this information for the purpose of patient education and counselling.

STUDY DESIGN

The data of pregnant women with red cell antibodies between January 2011 and December 2016 was obtained from the Trust's database and reconciled with the Fetal Medicine Unit records using Viewpoint©. Fetal anaemia requiring in utero transfusion (IUT) was defined as a Middle Cerebral Artery Peak Systolic Velocities ≥ 1.5multiple of the median expected for gestational age. The mean gestational age at delivery, and perinatal outcomes of the pregnancies were recorded.

RESULT

Overall, 398 of the 96, 692 pregnant women that were screened had red cell antibodies, giving a prevalence of 1: 242 pregnancies. The Anti- E and Anti-M antibodies were the most common (114 women; 28.6%, and 112 women; 28.1% respectively), but did not cause fetal anaemia in isolation, while anti-D alloimmunization was the predominant indication for in-utero transfusion (IUT). Anti-DE and anti-Kell antibodies had the highest mean number of transfusions per pregnancy. The mean gestational age at delivery was 34 ± 2weeks. Post-transfusion fetal demise was recorded in two hydropic fetuses, both at a gestational age of 25 weeks; giving a transfusion-related mortality rate of 2.5%.

CONCLUSION

The prevalence of red cell antibodies at West Yorkshire is lower compared with reports from other Caucasian populations.Nevertheless, these antibodies are important causes of iatrogenic preterm delivery and fetal morbidity. The prognosis is however good with prompt diagnosis and management.

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.

Blood group genotyping

Genomics is affecting all areas of medicine. In transfusion medicine, DNA-based genotyping is being used as an alternative to serological antibody-based methods to determine blood groups for matching donor to recipient. Most antigenic polymorphisms are due to single nucleotide polymorphism changes in the respective genes, and DNA arrays that target these changes have been validated by comparison with antibody-based typing. Importantly, the ability to test for antigens for which there are no serologic reagents is a major medical advance to identify antibodies and find compatible donor units, and can be life-saving. This review summarizes the evolving use and applications of genotyping for red cell and platelet blood group antigens affecting several areas of medicine. These include prenatal medicine for evaluating risk of fetal or neonatal disease and candidates for Rh-immune globulin; transplantation for bone marrow donor selection and transfusion support for highly alloimmunized patients and for confirmation of A2 status of kidney donors; hematology for comprehensive typing for patients with anemia requiring chronic transfusion; and oncology for patients receiving monoclonal antibody therapies that interfere with pretransfusion testing. A genomics approach allows, for the first time, the ability to routinely select donor units antigen matched to recipients for more than ABO/RhD to reduce complications. Of relevance, the growth of whole-genome sequencing in chronic disease and for general health will provide patients' comprehensive extended blood group profile as part of their medical record to be used to inform selection of the optimal transfusion therapy.

High-throughput, non-invasive prenatal testing for fetal rhesus D status in RhD-negative women: a systematic review and meta-analysis

BACKGROUND

High-throughput non-invasive prenatal testing (NIPT) for fetal Rhesus D (RhD) status could avoid unnecessary treatment with anti-D immunoglobulin for RhD-negative women found to be carrying an RhD-negative fetus. We aimed to assess the diagnostic accuracy of high-throughput NIPT for fetal RhD status in RhD-negative women not known to be sensitized to the RhD antigen, by performing a systematic review and meta-analysis.

METHODS

Prospective cohort studies of high-throughput NIPT used to determine fetal RhD status were included. The eligible population were pregnant women who were RhD negative and not known to be sensitized to RhD antigen. The index test was high-throughput, NIPT cell-free fetal DNA tests of maternal plasma used to determine fetal RhD status. The reference standard considered was serologic cord blood testing at birth. Databases including MEDLINE, EMBASE, and Science Citation Index were searched up to February 2016. Two reviewers independently screened titles and abstracts and assessed full texts identified as potentially relevant. Risk of bias was assessed using QUADAS-2. The bivariate and hierarchical summary receiver-operating characteristic (HSROC) models were fitted to calculate summary estimates of sensitivity, specificity, false positive and false negative rates, and the associated 95% confidence intervals (CIs).

RESULTS

A total of 3921 references records were identified through electronic searches. Eight studies were included in the systematic review. Six studies were judged to be at low risk of bias. The HSROC models demonstrated high diagnostic performance of high-throughput NIPT testing for women tested at or after 11 weeks gestation. In the primary analysis for diagnostic accuracy, women with an inconclusive test result were treated as having tested positive. The false negative rate (incorrectly classed as RhD negative) was 0.34% (95% CI 0.15 to 0.76) and the false positive rate (incorrectly classed as RhD positive) was 3.86% (95% CI 2.54 to 5.82). There was limited evidence for non-white women and multiple pregnancies.

CONCLUSIONS

High-throughput NIPT is sufficiently accurate to detect fetal RhD status in RhD-negative women and would considerably reduce unnecessary treatment with routine anti-D immunoglobulin. The applicability of these findings to non-white women and women with multiple pregnancies is uncertain.

RHD alleles among pregnant women with serologic discrepant weak D phenotypes from a multiethnic population and risk of alloimmunization

BACKGROUND

A considerable number of RHD alleles responsible for weak and partial D phenotypes have been identified. Serologic determination of these phenotypes is often doubtful and makes genetic analysis of RHD gene highly desirable in transfusion recipients and pregnant women. We analyzed the RHD gene in a cohort of pregnant women with doubtful D phenotypes.

METHODS

RHD genotyping was performed on 104 cases with D typing discrepancies or with history of serologic weak D phenotype. Laboratory-developed DNA tests, RHD BeadChip (Bioarray Solutions, Immucor), and sequencing were used to identify the RHD alleles.

RESULTS

Molecular analyses showed 23 of 104 (22%) pregnant women were RHD*weak D types 1, 2, or 3 and not at risk for anti-D. Fifty-one (49%) were RHD*weak partial 4.0, 6 RHD*weak D type 38 (6%), 1 RHD*weak D type 45 (1%), 1 RHD*weak D type 67 (1%), and potentially at risk for being alloimmunized and making anti-D. Partial D was identified in 22 of 104 (21%) patients and definitively at risk for anti-D.

DISCUSSION

Appropriate classification of RhD phenotypes is recommended for correct indication of RhIG in pregnant women. However, the serologic distinction between RhD-negative and RhD-positive phenotypes is a difficult task in the case of D variants due to the variations in serologic testing. Our results show a great variability in RHD variant alleles in pregnant women from this population of high admixture. According to these results, 78% of these obstetric patients are at risk for anti-D and candidates for RhIG.

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.

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.

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.