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

Clinical Performance of Cell-Free DNA for Fetal RhD Detection in RhD-Negative Pregnant Individuals in the United States

OBJECTIVE

To evaluate the performance of a cell-free DNA (cfDNA) assay that uses next-generation sequencing with quantitative counting templates for the clinical detection of the fetal RHD genotype in a diverse RhD-negative pregnant population in the United States.

METHODS

This retrospective cohort study was conducted in four U.S. health care centers. The same next-generation sequencing quantitative counting template cfDNA fetal RhD assay was offered to nonalloimmunized RhD-negative pregnant individuals as part of clinical care. Rh immune globulin (RhIG) was administered at the discretion of the clinician. The sensitivity, specificity, and accuracy of the assay were calculated considering the neonatal RhD serology results.

RESULTS

A total of 401 nonalloimmunized RhD-negative pregnant individuals who received clinical care in the period from August 2020 to November 2023 were included in the analysis. The D antigen cfDNA result was 100% concordant with the neonatal serology, resulting in 100% sensitivity, 100% positive predictive value (95% CI, 98.6-100% for both), 100% specificity, and 100% negative predictive value (95% CI, 97.4-100% for both). There were 10 pregnant individuals in whom the cfDNA analysis identified a non- RHD gene deletion, including RhDΨ (n=5) and RHD-CE-D hybrid variants (n=5). Rh immune globulin was administered antenatally to 93.1% of pregnant individuals, with cfDNA results indicating an RhD-positive fetus compared with 75.0% of pregnant individuals with cfDNA results indicating an RhD-negative fetus, signifying that clinicians were using the cfDNA results to guide pregnancy management.

CONCLUSION

This next-generation sequencing with quantitative counting templates cfDNA analysis for detecting fetal RhD status is highly accurate with no false-positive or false-negative results in 401 racially and ethnically diverse pregnant individuals with 100% follow-up of all live births. This study and prior studies of this assay support a recommendation to offer cfDNA screening for fetal Rh status as an alternative option to prophylactic RhIG for all nonalloimmunized RhD-negative individuals, which will result in more efficient and targeted prenatal care with administration of RhIG only when medically indicated.

Optimizing RhD Immune Globulin Use in Pregnancy

The global shortage of RhD immune globulin, formally acknowledged by the Food and Drug Administration in 2023, is ongoing but has improved in recent months. In response, the American College of Obstetricians and Gynecologists (ACOG) issued guidance in March 2024 on alternative strategies to conserve RhD immune globulin supplies. Our objective is to evaluate strategies for optimizing RhD immune globulin use in pregnancy amidst a global shortage.This clinical opinion reviews guidance on strategies to conserve RhD immune globulin. These include targeted administration based on non-invasive fetal RhD genotyping using cell-free DNA (cfDNA), the use of alternative RhD immune globulin products, and selective withholding of prophylaxis in early pregnancy loss under 12 weeks' gestation. ACOG guidance on the administration of RhD immune globulin in pregnancy differs from many countries worldwide, as well as the World Health Organization and the American Society of Family Planning.Targeted administration and the use of non-invasive cell-free DNA (cfDNA) testing for fetal RhD status have shown promising accuracy and reliability in studies across multiple countries, leading to reduced unnecessary prophylaxis and potential cost savings. Additionally, withholding RhD immune globulin in select early pregnancy losses could further conserve resources without increasing alloimmunization risk.This review underscores the need for evidence-based approaches to manage limited RhD immune globulin supplies effectively and suggests that targeted prophylaxis could benefit both patient outcomes and healthcare resource allocation in the face of global shortages. · Alternative RhD immune globulin strategies are vital amid ongoing global shortages.. · Targeted administration using cfDNA testing reduces unnecessary RhD immune globulin use.. · Consider withholding RhD immune globulin in <12-week pregnancy loss without instrumentation..

Clinical Validation of a Prenatal Cell-Free DNA Screening Test for Fetal RHD in a Large U.S. Cohort

OBJECTIVE

To present a large U.S. clinical validation of a next-generation sequencing-based, noninvasive prenatal cell-free DNA test for fetal RHD .

METHODS

This clinical validation study assessed the performance of a commercially available, next-generation sequencing-based cell-free DNA test for fetal RHD status. Samples that passed quality metrics were included if the patient had a previously reported cell-free DNA result for fetal aneuploidy, maternal RhD-negative serology, newborn RhD serology, and maternal RHD deletion or RHD-CE-D hybrid(r's) genotype. Dizygotic twin pregnancies were excluded. Maternal and fetal RHD genotypes were evaluated with prospective cell-free DNA next-generation sequencing analysis. At the time of analysis, investigators were blinded to fetal RhD status.

RESULTS

The cohort consisted of 655 pregnant patients with serologic results for RhD antigen. Patient demographics included a representative distribution of race and ethnicities in the RhD-negative U.S. population (74.0% White, 13.7% Hispanic, 7.0% Black, and 2.1% Asian). Cell-free DNA fetal RHD was not reported in two cases. There were zero false-negative cases; 356 of 356 fetuses were correctly identified as fetal RhD positive (sensitivity 100%, 95% CI, 98.9-100%). Of the 297 RhD-negative fetuses, 295 were correctly identified as RhD negative (specificity 99.3%, 95% CI, 97.6-99.8%). Of the fetuses with a negative RhD phenotype, the cell-free DNA test accurately identified three with the fetal RHD pseudogene ( RHDΨ) genotype.

CONCLUSION

Validation of this test in this large U.S. cohort of RhD-negative patients provides data on early and accurate noninvasive prenatal identification of fetal RHD genotype at 9 weeks of gestation or more. This test has the potential to assist patients and clinicians in the prevention and management of RhD alloimmunization.

Clinical Applications of Fetal Cell-Free DNA: State of the Science

Advances in technology have correlated with expanding prenatal genetic testing options for pregnant people. Leading medical organizations recommend cell-free DNA as the most sensitive screening test for trisomies 13, 18, and 21, as well as for fetal sex chromosome aneuploidies. The commercially available testing options go beyond these recommended tests, and prenatal care professionals should be familiar with the tests that their patients may choose despite being beyond the scope of current medical recommendations. This article explains updates in cell-free DNA technology and clinical considerations for prenatal care professionals, recognizing that this is a rapidly changing field of science and health care.

Characterization of blood bank and transfusion medicine practices for pregnant individuals with fetuses at risk of hemolytic disease in the United States

BACKGROUND

Hemolytic disease of the fetus and newborn (HDFN) is caused by maternal alloantibody-mediated destruction of fetal/neonatal red blood cells (RBCs). While the pathophysiology has been well-characterized, the clinical and laboratory monitoring practices are inconsistent.

METHODS

We surveyed 103 US institutions to characterize laboratory testing practices for individuals with fetuses at risk of HDFN. Questions included antibody testing and titration methodologies, the use of critical titers, paternal and cell-free fetal DNA testing, and result reporting and documentation practices.

RESULTS

The response rate was 44% (45/103). Most respondents (96%, 43/45) assess maternal antibody titers, primarily using conventional tube-based methods only (79%, 34/43). Among respondents, 51% (23/45) rescreen all individuals for antibodies in the third trimester, and 60% (27/45) perform paternal RBC antigen testing. A minority (27%, 12/45) utilize cell-free fetal DNA (cffDNA) testing to predict fetal antigen status. Maternal antibody titers are performed even when the fetus is not considered to be at risk of HDFN based on cffDNA or paternal RBC antigen testing at 23% (10/43) of sites that assess titers.

DISCUSSION

There is heterogeneity across US institutions regarding the testing, monitoring, and reporting practices for pregnant individuals with fetuses at risk of HDFN, including the use of antibody titers in screening and monitoring programs, the use of paternal RBC antigen testing and cffDNA, and documentation of fetal antigen results. Standardization of laboratory testing protocols and closer collaboration between the blood bank and transfusion medicine service and the obstetric/maternal-fetal medicine service are needed.

Cell-Free DNA Analysis for the Determination of Fetal Red Blood Cell Antigen Genotype in Individuals With Alloimmunized Pregnancies

OBJECTIVE

To evaluate the accuracy of next-generation sequencing-based quantitative cell-free DNA analysis for fetal antigen genotyping in individuals with alloimmunized pregnancies undergoing clinical testing in practices across the United States as early as 10 weeks of gestation, with the objective of identifying individuals with pregnancies at risk for hemolytic disease of the fetus and newborn and guiding management.

METHODS

This prospective cohort study included patients with alloimmunized pregnancies undergoing clinical fetal antigen cell-free DNA analysis between 10 0/7 and 37 0/7 weeks of gestation at 120 clinical sites. Both the pregnant person with the alloimmunized pregnancy and the neonates resulting from the pregnancies were included. The laboratory issued the cell-free DNA results prospectively as a part of clinical care. After delivery, neonatal buccal swabs collected between 0 and 270 days of life were sent to an outside independent laboratory for antigen genotyping. The outside laboratory was blinded to the fetal cell-free DNA results, and the results were compared. Concordance was reported for the fetal antigen cell-free DNA analysis for antigens to which the pregnant person was alloimmunized and for all antigens for which the pregnant person was genotype negative.

RESULTS

A total of 156 pregnant people who received clinically ordered cell-free DNA fetal antigen testing provided neonatal buccal swabs for genotyping after delivery. Overall, 15.4% of participants were Hispanic, 9.0% were non-Hispanic Black, 65.4% were non-Hispanic White, 4.5% were Asian, 1.3% were more than one race or ethnicity, and 4.5% were unknown. The median gestational age at the time of testing was 16.4 weeks with a median fetal fraction of 11.1%. Concordance between cell-free DNA analysis results and neonatal genotype was determined for 465 antigen calls for the following antigens: K1 (n=143), E (124), C (60), Fy a (50), c (47), and D(RhD) (41). These 465 calls included 145 in which the fetus was antigen positive and 320 in which the fetus was antigen negative. We observed complete concordance between prenatal fetal antigen cell-free DNA analysis results and neonatal genotypes for the 465 calls, resulting in 100% sensitivity, specificity, and accuracy.

CONCLUSION

In a diverse multicenter cohort, cell-free DNA analysis was highly sensitive and specific for determining fetal antigen genotype as early as 10 weeks of gestation in individuals with alloimmunized pregnancies. Taken together with previously published evidence, this study supports the implementation of cell-free DNA testing to manage individuals with alloimmunized pregnancies in the United States.

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.

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.

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.

Noninvasive Fetal RhD Blood Group Genotyping: A Systematic Review of Economic Evaluations

OBJECTIVE

Noninvasive fetal rhesus D (RhD) blood group genotyping may prevent unnecessary use of anti-D immunoglobulin (RhIG) in non-alloimmunized RhD-negative pregnancies and can guide management of alloimmunized pregnancies. We conducted a systematic review of the economic literature to determine the cost-effectiveness of this intervention over usual care.

DATA SOURCES

Systematic literature searches of bibliographic databases (Ovid MEDLINE, Embase, and Cochrane) until February 26, 2019, and auto-alerts until October 30, 2020, and of grey literature sources were performed to retrieve all English-language studies.

STUDY SELECTION

We included studies done in serologically confirmed non-alloimmunized or alloimmunized RhD-negative pregnancies, comparing costs and effectiveness of the intervention versus usual care.

DATA EXTRACTION AND SYNTHESIS

Two reviewers extracted data from the eligible studies and assessed their methodological quality (risk of bias) using the Quality of Health Economic Studies (QHES) and Drummond tools. We narratively synthesized findings. Our review included 8 economic studies that evaluated non-invasive fetal RhD genotyping followed by targeted RhIG prophylaxis in non-alloimmunized pregnancies. Five studies further considered a subsequent alloimmunized pregnancy. The cost-effectiveness of the intervention versus usual care (e.g., universal RhIG or prophylaxis conditional on results of paternal testing) for non-alloiummunized pregnancies was inconsistent. Two studies indicated greater benefits and lower costs for the intervention, and another 2 suggested a trade-off. In 4 studies, the intervention was less effective and costlier than alternatives. Three studies were determined to be of high quality by both tools. Two of these studies favoured the intervention, and one assessed benefits in quality-adjusted life-years. No study clearly examined the cost-effectiveness of repetitive use of fetal genotyping in multiple non-alloimmunized or alloimmunized pregnancies. The cost of genotyping was the most influential parameter.

CONCLUSION

The cost-effectiveness of noninvasive fetal RhD genotyping for non-alloimmunized pregnancies varies between studies. Potential savings from targeted management of alloimmunized pregnancies requires further research.

Diagnostic performance of the noninvasive prenatal FetoGnost RhD assay for the prediction of the fetal RhD blood group status

Purpose

To evaluate the diagnostic accuracy of a commercially available test kit for noninvasive prenatal determination of the fetal RhD status (NIPT-RhD) with a focus on early gestation and multiple pregnancies.

Methods

The FetoGnost RhD assay (Ingenetix, Vienna, Austria) is routinely applied for clinical decision making either in woman with anti-D alloimmunization or to target the application of routine antenatal anti-D prophylaxis (RAADP) to women with a RhD positive fetus. Based on existing data in the laboratory information system the newborn’s serological RhD status was compared with NIPT RhD results.

Results

Since 2009 NIPT RhD was performed in 2968 pregnant women between weeks 5 + 6 and 40 + 0 of gestation (median 12 + 6) and conclusive results were obtained in 2888 (97.30%) cases. Diagnostic accuracy was calculated from those 2244 (77.70%) cases with the newborn’s serological RhD status reported. The sensitivity of the FetoGnost RhD assay was 99.93% (95% CI 99.61–99.99%) and the specificity was 99.61% (95% CI 98.86–99.87%). No false-positive or false-negative NIPT RhD result was observed in 203 multiple pregnancies.

Conclusion

NIPT RhD results are reliable when obtained with FetoGnost RhD assay. Targeted routine anti-D-prophylaxis can start as early as 11 + 0 weeks of gestation in singleton and multiple pregnancies.

Noninvasive Fetal RhD Blood Group Genotyping: A Health Technology Assessment

BACKGROUND

RhD blood group incompatibility during pregnancy can cause serious health problems for the fetus. Noninvasive fetal RhD blood group genotyping is a test for fetal RhD status that may help prevent unnecessary preventive treatment (Rh immunoglobulin [RhIG] injections) and intensive pregnancy monitoring. We conducted a health technology assessment of noninvasive fetal RhD blood group genotyping for RhD-negative (RhD-) pregnancies. Our assessment evaluated the test's diagnostic accuracy, clinical utility, and cost-effectiveness, the budget impact of publicly funding this test, and patients' and providers' preferences and values.

METHODS

We performed a systematic literature search of the clinical and economic evidence to conduct an overview of reviews for test accuracy, a systematic review for clinical utility, and a review of the test's cost-effectiveness compared with usual care. We assessed the risk of bias of each included systematic review and study using the ROBIS and RoBANs tools, respectively. We assessed the quality of the body of clinical evidence according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group criteria. We developed probabilistic Markov microsimulation models to determine the cost-effectiveness and cost-utility of noninvasive fetal RhD genotyping compared with usual care from the Ontario Ministry of Health perspective. We also estimated the 5-year budget impact of publicly funding this test in Ontario. To examine patient and provider preferences related to noninvasive fetal RhD genotyping, we conducted a literature survey of quantitative studies on preference; the Canadian Agency for Drugs and Technologies in Health (CADTH) performed a review of qualitative literature about patient preferences; and we conducted interviews and an online survey with Ontario patients.

RESULTS

We included six systematic reviews in the overview of reviews on diagnostic test accuracy and 11 studies in the clinical utility review. Across systematic reviews, test accuracy was high for noninvasive fetal RhD genotyping. The evidence suggests that implementation of noninvasive fetal RhD genotyping may lead to avoidance of unnecessary RhIG prophylaxis (GRADE: Low), good compliance with targeted RhIG prophylaxis (GRADE: Very low), and high uptake of genotyping (GRADE: Low). Alloimmunization may not increase when using noninvasive fetal RhD genotyping to target prenatal RhIG prophylaxis (GRADE: Very low), and may allow unnecessary monitoring and invasive procedures to be avoided in alloimmunized pregnancies (GRADE: Very low).We included eight published economic studies that reported inconsistent results regarding the cost-effectiveness of noninvasive fetal RhD genotyping. In nonalloimmunized RhD- pregnancies, compared with usual care, the intervention identified more maternal alloimmunization cases (probability: 0.0022 vs. 0.0020) and was associated with a reduced number of RhIG injections per pregnancy (1.79 vs 1.43). It was more expensive ($154, 95% credible interval [CrI] $139 to $169) but had little impact on the QALYs of newborns followed over a 10-year time horizon (0.0007, 95% CrI -0.01 to 0.01). The cost of noninvasive fetal RhD genotyping and inclusion of paternal RhD typing were drivers of the cost-effectiveness results in this population. In alloimmunized RhD- pregnancies, noninvasive fetal RhD genotyping was associated with lower resource use during the pregnancy. Compared with usual care, it was less costly (-$6,280, 95% CrI -$6,325 to -$6,229) and more effective (0.19 QALYs, 95% CrI 0.17 to 0.20).The annual budget impact of publicly funding noninvasive fetal RhD genotyping in nonalloimmunized RhD- pregnancies in Ontario ranges from $2.6 million in year 1 (uptake of 80%) to $3.4 million in year 5 (uptake of 100%), with a 5-year total of about $14.8 million. In alloimmunized pregnancies, we estimate cost savings, from about $9 million in year 1 to about $12 million in year 5, with 5-year total savings of about $51.5 million.We included two studies in the survey of quantitative preferences literature. In the quantitative literature, RhD- pregnant people support routine offering of noninvasive fetal RhD genotyping as part of pregnancy care, with a preference to be adequately informed about the test process, attributes, timing, and risks in advance of the test, ideally in a dialogue with their health care provider. More than half of obstetric health care providers were supportive of offering the test. The qualitative review by CADTH and our own engagement with Ontario patients yielded similar results. Participants consistently expressed a desire for more information about the test and assurance about its safety. They also consistently mentioned the prevention of unnecessary monitoring and treatment as potential benefits.

CONCLUSIONS

Noninvasive fetal RhD blood group genotyping is an accurate test to determine RhD incompatibility and guide management of RhD- pregnancies. Compared with usual care, noninvasive fetal RhD genotyping is less costly and more effective for the management of alloimmunized pregnancies. For nonalloimmunized pregnancies, noninvasive fetal RhD genotyping would generally not be considered cost-effective, compared with usual care, unless the cost of testing is much lower than what is proposed now. Publicly funding noninvasive fetal RhD genotyping for guiding the management of RhD- pregnancies in Ontario over next 5 years is associated with a total budget impact of about $15 million in nonalloimmunized pregnancies and total cost savings of about $51 million in alloimmunized pregnancies. Patients and providers indicated support for the routine use of noninvasive fetal RhD genotyping in RhD- pregnancies.

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.

Red cell alloimmunization: A 2020 update

Management of maternal red cell alloimmunization has been revolutionized over the last 60 years. Advances in the prevention, screening, diagnosis, and treatment of alloimmune-induced fetal anemia make this condition an exemplar for contemporary practice in fetal therapy. Since survival is now an expectation, attention has turned to optimization of long-term outcomes following an alloimmunized pregnancy. In this review, the current management of red cell alloimmunization is described. Current research and future directions are discussed with particular emphasis on later life outcomes after alloimmune fetal anemia.

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.

Introduction of Noninvasive Prenatal Testing for Blood Group and Platelet Antigens from Cell-Free Plasma DNA Using Digital PCR

Background

Noninvasive prenatal testing (NIPT) for fetal antigens is a common standard for targeted immune prophylaxis in RhD-mediated hemolytic disease of the fetus and newborn, and is most frequently done by quantitative PCR (qPCR). A similar approach is considered for other blood group and human platelet alloantigens (HPA). Because of a higher sensitivity compared to qPCR for rare molecule detection, we established and validated digital PCR (dPCR) assays for the detection of RHD exons 3, 5 and 7, KEL1, HPA-1a, and HPA-5b from cell-free DNA (cfDNA) in plasma. The dPCR assays for the Y-chromosomal marker amelogenin and autosomal SNPs were implemented as controls for the proof of fetal DNA.

Methods

Validation was performed on dilution series of mixed plasma samples from volunteer donors with known genotypes. After preamplification of the target loci, two-color (FAM and VIC) TaqMan^TM probe chemistry and chip-based dPCR were applied. The assays for RHD included GAPDH as an internal control. For the diallelic markers KEL1/2, HPA-1a/b, HPA-5a/b, and AMEL-X/Y and 3 autosomal SNPs, the probes enabled allelic discrimination in the two fluorescence channels. The dPCR protocol for NIPT was applied to plasma samples from pregnant women.

Results

The RHD exon 5 assay allowed the detection of a 0.05% RHD target in an RhD-negative background, whereas the exon 7 assay required at least a 0.25% target. The exon 3 assay showed the highest background and required at least a 2.5% RHD target for reliable detection. The dPCR assays for the diallelic markers revealed similar sensitivity and enabled the detection of at least a 0.5% target allele. The HPA-1a assay was the most sensitive and allowed target detection in plasma mixtures containing only 0.05% HPA-1a. The plasma samples from 13 pregnant women at different gestational ages showed unambiguous positive and negative results for the analyzed targets.

Conclusion

Analysis of cfDNA from maternal plasma using dPCR is suitable for the detection of fetal alleles. Because of the high sensitivity of the assays, the NIPT protocol for RhD, KEL1, and HPA can also be applied to earlier stages of pregnancy.

Noninvasive fetal RHD genotyping to guide targeted anti-D prophylaxis-an external quality assessment workshop

BACKGROUND AND OBJECTIVES

Fetal RHD genotyping of cell-free fetal DNA from RhD-negative pregnant women can be used to guide targeted antenatal and postnatal anti-D prophylaxis for the prevention of RhD immunization. To assure the quality of clinical testing, we conducted an external quality assessment workshop with the participation of 28 laboratories.

MATERIALS AND METHODS

Aliquots of pooled maternal plasma were sent to each laboratory. One sample was positive, and the second sample was negative for fetal RHD, verified by pre-workshop testing using quantitative real-time PCR (qPCR) analysis of RHD exons 4, 5, 7 and 10. Plasma samples were shipped at room temperature. A reporting scheme was supplied for data collection, including questions regarding the methodological setup, results and clinical recommendations. Different methodological approaches were used, all employing qPCR with a total of eight different combinations of RHD exon targets. The samples were tested blindly.

RESULTS

Fetal RHD genotyping was performed with no false-negative and no false-positive results. One inconclusive result was reported for the RHD-positive sample, and four inconclusive results were reported for the RHD-negative sample. All clinical conclusions were satisfactory.

CONCLUSION

This external quality assessment workshop demonstrates that despite the different approaches taken to perform the clinical assays, fetal RHD genotyping is a reliable laboratory assay to guide targeted use of Rh prophylaxis in a clinical setting.

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.