Sensitivity of fetal RHD screening for safe guidance of targeted anti-D immunoglobulin prophylaxis: prospective cohort study of a nationwide programme in the Netherlands

How I use noninvasive prenatal testing for red blood cell and platelet antigens

ABSTRACT

Alloimmunization during pregnancy occurs when a mother produces antibodies against fetal antigens, leading to complications like hemolytic disease of the fetus and newborn (HDFN) and fetal and neonatal alloimmune thrombocytopenia (FNAIT). HDFN involves destruction of fetal red blood cells, potentially causing severe anemia, hydrops fetalis, and fetal death. FNAIT affects fetal platelets and possibly endothelial cells, resulting in risk of intracranial hemorrhage and brain damage. Traditional invasive methods for fetal antigen genotyping, like amniocentesis, carried miscarriage risks. The discovery of cell-free fetal DNA (cff-DNA) in maternal plasma enabled safe, noninvasive prenatal testing (NIPT). Initially used for Rhesus antigen D blood group typing, NIPT now covers various blood group antigens. Advances in technology have further enhanced the accuracy of NIPT. Despite challenges such as low cff-DNA fractions and complex genetic variations, NIPT has become essential in managing alloimmunized pregnancies. In NIPT it is important to prevent both false-positive results and false-negative results. Particularly in the coming decades, more possibilities for personalized antenatal treatment for HDFN and FNAIT cases will become apparent and accurate NIPT blood group antigen typing results are crucial for guiding clinical decisions. In this paper we describe this journey and provide practical tools for the clinic.

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..

Perinatal outcomes in RhD-negative pregnant women in Japan

Managing RhD-negative pregnancies is vital for preventing hemolytic disease of the fetus and newborn, which occurs when RhD-negative mothers develop anti-D antibodies after exposure to RhD-positive fetal blood. This retrospective cohort study evaluated the proportion of RhD-negative pregnancies and newborns in Japan by assessing current management practices and outcomes. This study included RhD-negative pregnant women who delivered at 22 weeks or later at 47 Japanese facilities between April 2018 and March 2023. Pregnancies with unknown newborn RhD status were excluded. Data were obtained from medical records. Among the 1088 RhD-negative women, 1062 met the inclusion criteria. RhD-negative pregnancies comprised 0.71% of the total cohort, with 8.7% RhD-negative newborns. Anti-D immunoglobulin was administered in 96.5% of pregnancies, with a maternal spontaneous sensitization rate of 0.6% before 28 weeks and no sensitization detected from 28 weeks to postpartum. Sensitized RhD-negative women had higher cesarean section, preterm delivery, and neonatal hemolytic anemia rates than the non-sensitized group, leading to increased neonatal intensive care unit admissions. Despite the low incidence of RhD-negative pregnancies, this study underscores the need for tailored management strategies, suggesting that non-invasive prenatal diagnosis of fetal RhD status could prevent unnecessary anti-D immunoglobulin administration, improving outcomes and resource utilization in Japan.

Real-world performance of a clinical droplet digital polymerase chain reaction assay for non-invasive foetal blood group and platelet antigen genotyping of alloimmunized pregnant women with antibodies directed against RhD, RhE, Rhc, RhC, K1, HPA-1a or HPA-5b: A 1-year experience

BACKGROUND AND OBJECTIVES

To test the performance of a new droplet digital polymerase chain reaction (ddPCR) non-invasive foetal blood group and platelet antigen genotyping assay in the setting of a Dutch reference laboratory for foetal blood group and platelet antigen genotyping. Our population comprised 229 consecutive alloimmunized pregnant women who presented between April 2022 and March 2023 with 250 requests for non-invasive foetal RHD, RHE, RHc, RHC, K1, HPA-1a or HPA-5b blood group and platelet antigen genotyping.

MATERIALS AND METHODS

Samples were genotyped for blood group and platelet antigen alleles along with methylated RASSF1a (mRASSF1a) and sex-determining region of Y (SRY) and DYS14 as positive foetal controls. Negative blood group and platelet antigen results were issued only when foetal controls were positive; otherwise, such samples were classified as inconclusive.

RESULTS

The assay achieved a success rate of 98.4% (246 of 250) because one case was lost to follow-up, one case was solved with quantitative polymerase chain reaction (qPCR) and one case precluded foetal typing due to RHD variant mothers. Only 10 cases needed a second sample and one case a third for a valid final result. We identified 116 maternal-foetal blood group and platelet antigen incompatibilities.

CONCLUSION

Clinical non-invasive foetal blood group and platelet antigen typing of alloimmunized pregnant women via ddPCR is successful and represents an improvement over qPCR because of the addition of a foetal control and because ddPCR circumvents potential interference from maternal cell-free DNA (cfDNA) background for foetal HPA-1 and K1.

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.

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.

Single-exon fetal RHD genotyping: a 31-month follow up in the obstetric population of Western Sweden

BACKGROUND

The Rh blood group system is highly complex, polymorphic, and immunogenic. The presence of RHD gene variants in RhD negative pregnant women is a challenge in fetal RHD genotyping as it may influence the antenatal management of anti-D prophylaxis. The aim of this study was to determine the efficiency of a non-invasive single-exon approach in the obstetric population of Western Sweden in a 31-month follow up. The frequency and type of maternal RHD variants were explored and the relation to the ethnicity was elucidated. Discrepant results between fetal RHD genotyping and serological blood group typing of newborns were investigated and clarified.

MATERIALS AND METHODS

RHD exon 4 was analysed with quantitative real-time PCR technique in a total of 6,948 blood samples from RhD negative women in early pregnancy. All cases with suspected maternal RHD gene and discrepant results observed in newborn samples, were further investigated using both serological and molecular technologies.

RESULTS

A total of 43 samples (0.6%) had inconclusive fetal genotyping result due the presence of a maternal RHD gene. These findings were in most cases (>66%) observed in pregnant women of non-European ancestry. Additionally, two novel RHD alleles were found. Seven discrepant results between fetal RHD genotype and serological RhD type of the newborns, were shown to be related to D antigen variants in newborns. Assay sensitivity was 99.95%, specificity 100%, and accuracy 99.97%.

DISCUSSION

The single-exon approach for fetal RHD screening early in pregnancy is an appropriate choice in the population of Western Sweden, with a very low frequency of inconclusive results caused by the presence of maternal RHD gene variants. Due to the high sensitivity, specificity, and accuracy of the test, serological typing of neonates born to RhD negative women has no longer been performed at our laboratory since June 2023.

Maternal red blood cell alloimmunization prevalence in the United States

ABSTRACT

Hemolytic disease of fetus and newborn (HDFN) is a life-threatening disease mediated by maternal alloimmunization to red blood cell (RBC) antigens. Studies of maternal alloimmunization prevalence in the United States lack national data. This study describes prevalence and trends in alloimmunization in pregnancy in the United States. RBC antibodies (abs) were identified in a large, nationwide, commercial laboratory database from 2010 through 2021. The cohort comprised pregnancies for which the year of laboratory collection and patient's state of residence were available. Data were normalized based on US Centers for Disease Control and Prevention estimates of live births and weighted by year and US Census Division. Cochrane-Armitage tests assessed temporal trends of alloimmunization. Of 9 876 196 pregnancies, 147 262 (1.5%) screened positive for RBC abs, corresponding to an estimated prevalence of 1518 of 100 000 pregnancies. Of identified RBC abs, anti-D comprised 64.1% pregnancies (586/100 000). Prevalence of other high-risk RBC abs for HDFN included anti-K (68/100 000) and anti-c (29/100 000). Incidence of all 3 high-risk abs increased from 2010 to 2021 (all P < .001). Among almost 10 million pregnancies in the United States, comprising an estimated 14.4% of all pregnancies, 1.5% screened positive for RBC abs. Almost three-quarters (679/100 000 [74.3%]) of RBC abs identified were high risk for HDFN. Although prevalence of anti-D is difficult to interpret without the ability to distinguish alloimmunization from passive immunity, it remains problematic in HDFN, ranking second only to anti-K in critical titers. Given the sequelae of HDFN, new initiatives are required to reduce the incidence of alloimmunization in patients of reproductive potential.

Nipocalimab in Early-Onset Severe Hemolytic Disease of the Fetus and Newborn

BACKGROUND

In early-onset severe hemolytic disease of the fetus and newborn (HDFN), transplacental transfer of maternal antierythrocyte IgG alloantibodies causes fetal anemia that leads to the use of high-risk intrauterine transfusions in order to avoid fetal hydrops and fetal death. Nipocalimab, an anti-neonatal Fc receptor blocker, inhibits transplacental IgG transfer and lowers maternal IgG levels.

METHODS

In an international, open-label, single-group, phase 2 study, we assessed treatment with intravenous nipocalimab (30 or 45 mg per kilogram of body weight per week) administered from 14 to 35 weeks' gestation in participants with pregnancies at high risk for recurrent early-onset severe HDFN. The primary end point was live birth at 32 weeks' gestation or later without intrauterine transfusions as assessed against a historical benchmark (0%; clinically meaningful difference, 10%).

RESULTS

Live birth at 32 weeks' gestation or later without intrauterine transfusions occurred in 7 of 13 pregnancies (54%; 95% confidence interval, 25 to 81) in the study. No cases of fetal hydrops occurred, and 6 participants (46%) did not receive any antenatal or neonatal transfusions. Six fetuses received an intrauterine transfusion: five fetuses at 24 weeks' gestation or later and one fetus before fetal loss at 22 weeks and 5 days' gestation. Live birth occurred in 12 pregnancies. The median gestational age at delivery was 36 weeks and 4 days. Of the 12 live-born infants, 1 received one exchange transfusion and one simple transfusion and 5 received only simple transfusions. Treatment-related decreases in the alloantibody titer and IgG level were observed in maternal samples and cord blood. No unusual maternal or pediatric infections were observed. Serious adverse events were consistent with HDFN, pregnancy, or prematurity.

CONCLUSIONS

Nipocalimab treatment delayed or prevented fetal anemia or intrauterine transfusions, as compared with the historical benchmark, in pregnancies at high risk for early-onset severe HDFN. (Funded by Janssen Research and Development; UNITY ClinicalTrials.gov number, NCT03842189.).

Why do RhD negative pregnant women still become anti-D immunized despite prophylaxis with anti-D immunoglobulin?

Maternal allo-anti-D in RhD negative pregnant women may cause mild to severe hemolytic disease of the fetus and newborn. Although several other antibodies may also destroy red blood cells of the fetus and newborn, preventive measures with anti-D immunoglobulin are only available for D antigen. Targeted antenatal care together with postpartum prophylaxis with anti-D immunoglobulin has significantly reduced the D-alloimmunization risk. Potentially sensitizing events like trauma to the pregnant abdomen, vaginal bleeding, and amniocentesis may lead to fetomaternal hemorrhage and necessitate additional doses. Despite comprehensive programs with these targeted measures, allo-anti-D is still the most common reason for severe hemolytic disease of the fetus and newborn. Where do we fail then? Here, in this review, I would therefore like to discuss the reasons for D-alloimmunizations hoping that the greater focus will pave the way for further reduction in the number of pregnancy-related allo-anti-Ds.

Red Blood Cell Alloimmunization in Pregnancy: A Review of the Pathophysiology, Prevalence, and Risk Factors

This review paper provides an overview of the risk factors and laboratory testing for red blood cell (RBC) alloimmunization in pregnancy. RBC alloimmunization is a significant medical issue that can cause haemolytic disease of the fetus and newborn (HDFN), leading to neonatal morbidity and mortality. Current HDFN prophylaxis targets only Rhesus D (RhD) alloimmunization, with no effective measures to prevent alloimmunization to other RBC antigen groups. Several factors can increase the risk of developing RBC alloimmunization during pregnancy, including fetomaternal haemorrhage, RBC and maternal genetic status, and previous transfusions. Identifying these risk factors is essential to execute the appropriate management strategies to minimize the risk of HDFN. The review also discusses the laboratory methods and overview of pregnancy management. The paper highlights the importance of identifying and managing the risk factors for RBC alloimmunization in pregnancy to minimize the risk of HDFN and improve neonatal outcomes.

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.

Evaluation of an automated platform for non-invasive single-exon fetal RHD genotyping early in pregnancy

BACKGROUND

RhD immunization is still the major cause of hemolytic disease of the fetus and newborn. Fetal RHD genotyping during pregnancy followed by tailored anti-D prophylaxis for pregnant RhD-negative women carrying an RHD-positive fetus to prevent RhD immunization is a well-established practice in many countries. This study aimed to validate a platform for high-throughput, non-invasive, single-exon, fetal RHD genotyping consisting of automated DNA extraction and PCR set-up, and a novel system for electronic data transfer to the real-time PCR instrument. We also investigated the effect of storage conditions of fresh or frozen samples on the outcome of the assay.

MATERIALS AND METHODS

Blood samples from 261 RhD-negative pregnant women collected in Gothenburg, Sweden, between November 2018 and April 2020 during gestation week 10-14 were either tested as fresh after storage for 0-7 days at room temperature or as thawed plasma samples previously separated and stored for up to 13 months at -80°C. Extraction of cell-free fetal DNA and PCR set-up were performed in a closed automated system. Fetal RHD genotyping was determined by real-time PCR amplification of the RHD gene exon 4.

RESULTS

The outcome of RHD genotyping was compared with either the results obtained with serological RhD typing of newborns or with the results of RHD genotyping performed by other laboratories. No difference was observed in genotyping results when using fresh or frozen plasma during short- and long-term storage, revealing high stability of cell-free fetal DNA. The assay has shown high sensitivity (99.37%), specificity (100%), and accuracy (99.62%).

DISCUSSION

These data confirm that the proposed platform for non-invasive, single-exon, RHD genotyping early in pregnancy is accurate and robust. Importantly, we demonstrated the stability of cell-free fetal DNA in fresh and frozen samples after short- and long-term storage.

Terminating Routine Cord Blood RhD Typing of the Newborns to Guide Postnatal Anti-D Immunoglobulin Prophylaxis Based on the Results of Fetal RHD Genotyping

INTRODUCTION

Targeted routine antenatal prophylaxis with anti-D immunoglobulin (Ig) only to RhD-negative pregnant women who carry RhD-positive fetuses (determined by fetal RHD genotyping) has reduced D-alloimmunization significantly when administered in addition to postnatal prophylaxis. Achieving high analysis sensitivity and few false-negative fetal RHD results will make RhD typing of the newborn redundant. Postnatal prophylaxis can then be given based on the result of fetal RHD genotyping. Terminating routine RhD typing of the newborns in cord blood will streamline maternity care. Accordingly, we compared the results of fetal RHD genotyping with RhD typing of the newborns.

METHODS

Fetal RHD genotyping was performed, and antenatal anti-D Ig was administered at gestational week 24 and 28, respectively. Data for 2017-2020 are reported.

RESULTS

Ten laboratories reported 18,536 fetal RHD genotypings, and 16,378 RhD typing results of newborns. We found 46 false-positive (0.28%) and seven false-negative (0.04%) results. Sensitivity of the assays was 99.93%, while specificity was 99.24%.

CONCLUSION

Few false-negative results support the good analysis quality of fetal RHD genotyping. Routine cord blood RhD typing will therefore be discontinued nationwide and postnatal anti-D Ig will now be given based on the result of fetal RHD genotyping.

Reappraisal of evolving methods in non-invasive prenatal screening: Discovery, biology and clinical utility

Non-invasive prenatal screening (NIPS) offers an opportunity to screen or determine features associated with the fetus. Earlier, prenatal testing was done with cytogenetic procedures like karyotyping or fluorescence in-situ hybridization, which necessitated invasive methods such as fetal blood sampling, chorionic villus sampling or amniocentesis. Over the last two decades, there has been a paradigm shift away from invasive prenatal diagnostic methods to non-invasive ones. NIPS tests heavily rely on cell-free fetal DNA (cffDNA). This DNA is released into the maternal circulation by placenta. Like cffDNA, fetal cells such as nucleated red blood cells, placental trophoblasts, leukocytes, and exosomes or fetal RNA circulating in maternal plasma, have enormous potential in non-invasive prenatal testing, but their use is still limited due to a number of limitations. Non-invasive approaches currently use circulating fetal DNA to assess the fetal genetic milieu. Methods with an acceptable detection rate and specificity such as sequencing, methylation, or PCR, have recently gained popularity in NIPS. Now that NIPS has established clinical significance in prenatal screening and diagnosis, it is critical to gain insights into and comprehend the genesis of NIPS de novo. The current review reappraises the development and emergence of non-invasive prenatal screen/test approaches, as well as their clinical application, with a focus, on the scope, benefits, and limitations.

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.

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.

Laboratory Monitoring of Mother, Fetus, and Newborn in Hemolytic Disease of Fetus and Newborn

Background

Laboratory monitoring of mother, fetus, and newborn in hemolytic disease of fetus and newborn (HDFN) aims to guide clinicians and the immunized women to focus on the most serious problems of alloimmunization and thus minimize the consequences of HDFN in general and of anti-D in particular. Here, we present the current approach of laboratory screening and testing for prevention and monitoring of HDFN at the Copenhagen University Hospital in Denmark.

Summary

All pregnant women are typed and screened in the 1st trimester. This serves to identify the RhD-negative pregnant women who at gestational age (GA) of 25 weeks are offered a second screen test and a non-invasive fetal RhD prediction. At GA 29 weeks, and again after delivery, non-immunized RhD-negative women carrying an RhD-positive fetus are offered Rh immunoglobulin. If the 1st trimester screen reveals an alloantibody, antenatal investigation is initiated. This also includes RhD-positive women with alloantibodies. Specificity and titer are determined, the fetal phenotype is predicted by non-invasive genotyping based on cell-free DNA (RhD, K, Rhc, RhC, RhE, ABO), and serial monitoring of titer commences. Based on titers and specificity, monitoring with serial peak systolic velocity measurements in the fetal middle cerebral artery to detect anemia will take place. Intrauterine transfusion is given when fetal anemia is suspected. Monitoring of the newborn by titer and survival of fetal red blood cells by flow cytometry will help predict the length of the recovery of the newborn.

Hemolytic Disease of the Newborn: A Review of Current Trends and Prospects

Hemolytic disease of the newborn (HDN), also known as Erythroblastosis fetalis, is a hemolytic condition that predominantly affects rhesus-positive fetuses and infants born to rhesus-negative mothers. The pathophysiology of HDN begins with maternal antibodies attacking fetal red blood cells following alloimmunization due to rhesus or ABO incompatibility between the maternal and fetal blood. Previously, HDN was known to cause fetal death in 1% of all pregnancies, but with the advent of immunoprophylactic therapies, the condition can be currently fairly well managed with fewer complications if diagnosed early. Diagnosis calls for extensive history taking, physical examination, serological studies, and imaging modalities such as pelvic ultrasound scans. To prevent the disease, earlier intravenous immunoglobulin (IVIG) should be given to pregnant Rh- women who have not been sensitized. It is also vital to understand prospective complications such as severe hyperbilirubinemia and develop appropriate remedies. Because of its great incidence and nature, HDN has been thoroughly explored, and more studies are being conducted each year, revealing new insights about the condition. This review covers the disorder's etiology, diagnosis, and management, including the most current findings as of 2021, as well as trends and prospects, to help in future research and evidence-based medical practice.

Improved library preparation protocols for amplicon sequencing-based noninvasive fetal genotyping for RHD-positive D antigen-negative alleles

Objective

We aimed to simplify our fetal RHD genotyping protocol by changing the method to attach Illumina’s sequencing adaptors to PCR products from the ligation-based method to a PCR-based method, and to improve its reliability and robustness by introducing unique molecular indexes, which allow us to count the numbers of DNA fragments used as PCR templates and to minimize the effects of PCR and sequencing errors.

Results

Both of the newly established protocols reduced time and cost compared with our conventional protocol. Removal of PCR duplicates using UMIs reduced the frequencies of erroneously mapped sequences reads likely generated by PCR and sequencing errors. The modified protocols will help us facilitate implementing fetal RHD genotyping for East Asian populations into clinical practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05793-4.

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.

Next-generation sequencing of 35 RHD variants in 16 253 serologically D- pregnant women in the Finnish population

Fetal RHD screening for targeted routine antenatal anti-D prophylaxis has been implemented in many countries, including Finland, since the 2010s. Comprehensive knowledge of the RHD polymorphism in the population is essential for the performance and safety of the anti-D prophylaxis program. During the first 3 years of the national screening program in Finland, over 16 000 samples from RhD- women were screened for fetal RHD; among them, 79 samples (0.5%) containing a maternal variant allele were detected. Of the detected maternal variants, 35 cases remained inconclusive using the traditional genotyping methods and required further analysis by next-generation sequencing (NGS) of the whole RHD gene to uncover the variant allele. In addition to the 13 RHD variants that have been previously reported in different populations, 8 novel variants were also detected, indicating that there is more variation of RHD in the RhD- Finnish population than has been previously known. Three of the novel alleles were identified in multiple samples; thus, they are likely specific to the original Finnish population. National screening has thus provided new information about the diversity of RHD variants in the Finnish population. The results show that NGS is a powerful method for genotyping the highly polymorphic RHD gene compared with traditional methods that rely on the detection of specific nucleotides by polymerase chain reaction amplification.

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.

The Norwegian experience with nationwide implementation of fetal RHD genotyping and targeted routine antenatal anti-D prophylaxis

OBJECTIVES

To reduce the risk of RhD alloimmunization during the last trimester of pregnancy, a targeted routine antenatal anti-D prophylaxis (RAADP) programme was implemented in Norway in 2016. Here, we present and discuss our experience with the nationwide implementation of the programme, and report sample uptake and preliminary data of de novo anti-D in pregnancy.

BACKGROUND

The targeted RAADP was advised by the academic community and evaluated by the health authorities. A National Working Group has conducted the implementation in the transfusion services and contributed to organise the administration of the antenatal anti-D prophylaxis. Fetal RhD type is determined by non-invasive prenatal testing at gestational week 24, and anti-D prophylaxis is administrated at gestational week 28 only to women with RhD positive fetuses.

METHODS

We describe the implementation process of targeted RAADP in Norway. The sample uptake is calculated by comparing the number of fetal RHD screens with the expected number of samples.

RESULTS

The sample uptake shows regional variations: 88%-100% after 3 years. Promising decrease in de novo anti-D detected during pregnancy is observed.

CONCLUSIONS

Nationwide targeted RAADP is implemented and included in the Norwegian maternity care programme. Compliance to sample uptake should further improve in some regions. A remaining issue to fulfil is the documentation of the accuracy of the fetal RHD-typing at all sites. Post-natal prophylaxis will then be guided by the fetal RHD result. Dedicated registries will ensure data to evaluate the expected reduction in pregnancy-related RhD immunisations, which is the final success criterion of the programme.

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.

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.

RhIg for the prevention Rh immunization and IVIg for the treatment of affected neonates

Rhesus D (RhD) negative pregnant women carrying an RhD positive fetus are at risk of developing anti-D during or after pregnancy. Anti-d-immunoglobulin (RhIg), which is mainly produced from special plasma donated in a few countries for the whole world, is able to prevent an anti-D alloimmunization. Through the introduction of ante- and postnatal anti-d-prophylaxis into clinical routine, the frequency of hemolytic disease of fetus and newborn decreased considerably. Postnatal prophylaxis from the beginning in the 1960s has been applied only to women who delivered an RhD positive newborn. Because the fetal RhD status can be determined with high sensitivity and accuracy from the mother's peripheral blood, targeted antenatal anti-d-prophylaxis is becoming a new standard procedure in more and more countries. Phototherapy and exchange transfusion are still the main pillars for the treatment of RhD hemolytic disease of the newborn. The efficacy of IVIg in the management of these neonates is not conclusive and cannot be recommended until a larger randomized, double-blind, placebo-controlled study is performed.

Antenatal and postpartum prevention of Rh alloimmunization: A systematic review and GRADE analysis

BACKGROUND

Existing systematic reviews of Rh immunoprophylaxis include only data from randomized controlled trials, have dated searches, and some do not report on all domains of risk of bias or evaluate the certainty of the evidence. Our objective was to perform an updated review, by including new trials, any comparative observational studies, and assessing the certainty of the evidence using the GRADE framework.

METHODS

We searched MEDLINE, Embase and the Cochrane Library from 2000 to November 26, 2019. Relevant websites and bibliographies of systematic reviews and guidelines were searched for studies published before 2000. Outcomes of interest were sensitization and adverse events. Risk of bias was evaluated with the Cochrane tool and ROBINS-I. The certainty of the evidence was performed using the GRADE framework.

RESULTS

Thirteen randomized trials and eight comparative cohort studies were identified, evaluating 12 comparisons. Although there is some evidence of beneficial treatment effects (e.g., at 6-months postpartum, fewer women who received RhIg at delivery compared to no RhIg became sensitized [70 fewer sensitized women per 1,000 (95%CI: 67 to 71 fewer); I2 = 73%]), due to very low certainty of the evidence, the magnitude of the treatment effect may be overestimated. The certainty of the evidence was very low for most outcomes often due to high risk of bias (e.g., randomization method, allocation concealment, selective reporting) and imprecision (i.e., few events and small sample sizes). There is limited evidence on prophylaxis for invasive fetal procedures (e.g. amniocentesis) in the comparative literature, and few studies reported adverse events.

CONCLUSION

Serious risk of bias and low to very low certainty of the evidence is found in existing RCTs and comparative observational studies addressing optimal effectiveness of Rh immunoprophylaxis. Guideline development committees should exercise caution when assessing the strength of the recommendations that inform and influence clinical practice in this area.

Two Reliable Methodical Approaches for Non-Invasive RHD Genotyping of a Fetus from Maternal Plasma

Noninvasive fetal RHD genotyping is an important tool for predicting RhD incompatibility between a pregnant woman and a fetus. This study aimed to assess a methodological approach other than the commonly used one for noninvasive fetal RHD genotyping on a representative set of RhD-negative pregnant women. The methodology must be accurate, reliable, and broadly available for implementation into routine clinical practice. A total of 337 RhD-negative pregnant women from the Czech Republic region were tested in this study. The fetal RHD genotype was assessed using two methods: real-time PCR and endpoint quantitative fluorescent (QF) PCR. We used exon-7-specific primers from the RHD gene, along with internal controls. Plasma samples were analyzed and measured in four/two parallel reactions to determine the accuracy of the RHD genotyping. The RHD genotype was verified using DNA analysis from a newborn buccal swab. Both methods showed an excellent ability to predict the RHD genotype. Real-time PCR achieved its greatest accuracy of 98.6% (97.1% sensitivity and 100% specificity (95% CI)) if all four PCRs were positive/negative. The QF PCR method also achieved its greatest accuracy of 99.4% (100% sensitivity and 98.6% specificity (95% CI)) if all the measurements were positive/negative. Both real-time PCR and QF PCR were reliable methods for precisely assessing the fetal RHD allele from the plasma of RhD-negative pregnant women.

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.

Rhesus D factor (RhD) negative women's experiences with pregnancy: An interpretive description

BACKGROUND

The development of rh immune globulin (RhIG) for the prevention of Rhesus D (RhD) alloimmunization has significantly decreased the incidence of RhD alloimmunization. Despite long-standing prevention, the experiences of RhD negative women with pregnancy is absent in the literature.

AIM

The purpose of this study was to explore the experiences of RhD negative women with pregnancy.

METHODS

Utilizing an Interpretive Description approach, semi-structured interviews were conducted with RhD negative women about their pregnancies. This study took place within the geographic context of northern British Columbia (BC). The analysis involved a two-cycle approach to identify themes within the data.

FINDINGS

Sixteen RhD negative women that live in northern BC participated in this study. The analysis identified that RhD negative women are uninformed and want to be involved in the decision-making process regarding the prevention of RhD alloimmunization. The themes that emerged from the interview data were communication, information-seeking behaviour, out of sight out of mind, choice and trust, and patient advocacy.

DISCUSSION

The participants in this study described lacking information regarding the prevention of RhD alloimmunization. They sought information to overcome the gaps in knowledge and a desire to be involved in the decision-making process.

CONCLUSION

RhD negative women want information and to be involved in the decision-making process in the prevention of RhD alloimmunization. Working with RhD negative women to develop decision-aids and/or other educational tools to aid in the decision-making process are warranted.

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.

A Multicenter, Randomized, Open-Label Trial Comparing the Efficacy and Safety of Monoclonal Anti-Rh (D) Immunoglobulin with Polyclonal Anti-Rh (D) Immunoglobulin for the Prevention of Maternal Rh-Isoimmunization

OBJECTIVES

To compare the efficacy and safety of monoclonal anti-Rhesus (anti-D) immunoglobulin (IgG) with polyclonal anti-D IgG in the prevention of maternal Rh-isoimmunization.

METHODS

This was a randomized, multicenter, open-label, comparative clinical trial conducted in the obstetric in-patient departments of nine tertiary care hospitals in India. 206 Rhesus (D)-negative women, not sensitized to Rh antigen, and delivering Rh positive babies, received postpartum intramuscular administration of monoclonal or polyclonal anti-D IgG. The main outcome measures were the proportion of subjects protected from Rh-isoimmunization, identified by a negative indirect Coombs test (ICT) result, at day 180 after anti-D IgG administration, and incidence of adverse events.

RESULTS

105 subjects were randomized to the monoclonal group and 101 to the polyclonal group. 94 from the monoclonal group had a negative ICT result and none had a positive ICT result at day 180, whereas 87 from the polyclonal group had a negative ICT result and one had a positive ICT result; the rest (11 and 13 subjects respectively) were lost to follow-up. A total of 5 adverse events were reported (3 in the monoclonal group and 2 in the polyclonal group); only one of these was serious. All the adverse events were judged to be unrelated to the interventional drug. None of the subjects in the monoclonal group developed immunogenic reaction to the monoclonal anti-D.

CONCLUSION

The efficacy and safety of the monoclonal preparation of anti-D was comparable to the polyclonal preparation of anti-D when used in the prevention of maternal Rh-isoimmunization.Trial registration Clinical Trial Registration Number: CTRI/2015/09/006172.

Amplicon Sequencing-Based Noninvasive Fetal Genotyping for RHD-Positive D Antigen-Negative Alleles

BACKGROUND

To avoid hemolytic disease of the fetus and newborn resulting from maternal alloantibodies against fetal Rh antigens, anti-D immunoglobulin is routinely administered to RhD-negative pregnant women in Japan. Fetal RHD genotyping using cell-free DNA may prevent unnecessary antibody administration; however, current PCR-based methods, which detect RHD deletion, do not address the higher rates of RHD-positive D antigen-negative alleles in nonwhite populations without additional inspections.

METHODS

We developed an amplicon-sequencing method that could estimate the type of paternally inherited fetal RHD allele from 4 major RHD alleles in the Japanese population: the D antigen-positive allele (RHD*01, 92.9%) and 3 D antigen-negative alleles (RHD*01N.01, 6.6%; RHD*01EL.01, 0.3%; RHD*01N.04, 0.1%) using cell-free DNA obtained from the blood plasma of pregnant women.

RESULTS

The method correctly determined the fetal RhD type even when RhD-negative pregnant women possessed an RHD-positive D antigen-negative allele: RHD*01EL.01 or RHD*01N.04.

CONCLUSIONS

This method is a reliable noninvasive fetal RHD genotyping method for Japanese and other East Asian populations. The genotyping principle of amplifying 2 different regions using the same primer pair and distinguishing them by their sequence difference during the subsequent mapping procedure is also theoretically applicable to RHD-positive D antigen-negative alleles prevalent in Africans. Therefore, this method offers an opportunity to consider targeted administration of anti-D immunoglobulin to RhD-negative pregnant women in East Asian and African countries and to increase the specificity of the fetal RHD genotyping implemented nationwide in several European countries.

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.

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.

Developments beyond blood group serology in the genomics era

Blood group serology and single nucleotide polymorphism-based genotyping platforms are accurate but do not provide a comprehensive cover for all 36 blood group systems and do not cover the antigen diversity observed among population groups. This review examines the extent to which genomics is shaping blood group serology. Resources for genomics include the Human Reference Genome Sequence assembly; curated blood group tables listing variants; public databases providing information on genetic variants from world-wide studies; and massively parallel sequencing technologies. Blood group genomic studies span the spectrum, from bioinformatic data mining of huge data sets containing whole genome and whole exome information to laboratory investigations utilising targeted sequencing approaches. Blood group predictions based on genome sequencing and genomic studies are proving accurate, and have shown utility in both research and reference settings. Overall, studies confirm the potential for blood group genomics to reshape donor and patient transfusion management strategies to provide more compatible blood transfusions.

Prediction of fetal blood group and platelet antigens from maternal plasma using next-generation sequencing

BACKGROUND

Fetuses whose mothers have produced antibodies to red blood cell (RBC) or platelet antigens are at risk of being affected by hemolytic disease or alloimmune thrombocytopenia, respectively, only if they inherit the incompatible antigen. Noninvasive diagnosis of the fetal antigen is employed for management of immunized pregnancies, but the specific detection of SNPs, encoding the majority of antigens, in maternal plasma is still a challenge. We applied targeted next-generation sequencing (NGS) to predict the fetal antigen based on the detection of fetomaternal chimerism.

METHODS AND MATERIALS

The DNA of 13 pregnant women (with anti-K [3] anti-k [1], anti-Fy^a [1], anti-D + C + Jk^a [1], anti-D + E + K [1], anti-HPA-1a [1], anti-HPA-3b [1], anti-HPA-5b [1], and nonimmunized [3]) was sequenced using primers for regions encoding RhD, RhC, Rhc, RhE/e, K/k, Fya/b, Jka/b, MN, Ss, and HPA-1, 2, 3, 5, 15, 4 X-polymorphisms on the Ion Torrent Personal Genome Machine (PGM) System (Thermo Fisher Scientific, Inc., Waltham, MA, USA).

RESULTS

NGS results were in agreement with the phenotype/genotype of women and their neonates (except for the unsuccessful detection of MN and RhC). NGS determined fetal allele chimerism for K, k, Fya, Fyb, Jka, Jkb, S, RhE (from 0.42% to 6.08%); RhD, Rhc (100%); HPA-1a, -2b, -3a, 3b, -5b, -15a, 15b (from 0.23% to 4.11%). NGS revealed fetal chimerism for incompatible antigens (from 0.7% to 4.8%) in 7 immunized cases, excluded in 3 (with anti-K, anti-Fy^a , anti-HPA-3b).

CONCLUSION

The designed NGS predicts the fetal RBC and platelet antigen status universally in cases with various clinically significant antibodies as well as providing confirmation of the presence of fetal DNA. However, some improvement of the unsuccessful primers is required.

Usefulness of Non-Invasive Fetal RHD Genotyping towards Immunoprophylaxis Optimization

Introduction: Since anti-D immunoprophylaxis given to D-negative pregnant women is a blood product, blood donations have an impact on the availability of prophylactic doses. The Pan American Health Organization reported, in June 2017, that less than half of blood donors are volunteers in Latin America and the Caribbean. In these countries, guidelines for use of anti-D prophylaxis are still controversial. The aim of this study was to demonstrate the convenience of a simple and cost-effectivene non-invasive prenatal diagnostic assay for anti-D prophylaxis optimization in multiethnic populations. Methods: Cell-free fetal DNA from plasma samples of D-negative pregnant women were analyzed by real-time PCR for simultaneous amplification of sequences of exons 5 and 10 of the RHD gene. Fetal RHD genotype was determined in 111 pregnant women. Neonates' phenotype was determined 72 h after birth. Results: Genotyping predicted fetal phenotype with 100% accuracy. Prenatal diagnosis showed 78% RHD-positive and 22% RHD-negative neonates. Conclusion: We demonstrated that, beyond the large genetic variation of the Rh system and the numerous D variants present in multiethnic groups, non-invasive fetal RHD genotyping using two sequences of the gene can be enough for clinical application in an admixed population. This robust technique of simple implementation allows to determine fetal RHD in maternal blood with high sensitivity, specificity, and accuracy. The introduction of fetal RhD genotyping as part of an antenatal screening program constitutes a reliable manner to optimize anti-D prophylaxis; however, it has not been implemented so far in most American countries.

Fetal anemia

The diagnosis and management of fetal anemia has been at the forefront of advances in the fields of fetal physiology, immunology, fetal imaging, and fetal therapy among others. Alloimmunization and parvovirus infection are the leading cause of fetal anemia in the United States. The middle cerebral artery peak systolic velocity (MCA-PSV) diagnoses fetal anemia. Its discovery is considered one of the most important achievements in fetal medicine. Accumulation of experience in recent years as well as refinement of surgical techniques have led to safer invasive procedures. It is expected that long term follow-up of affected pregnancies, continues to reflect all these improvements in care. It is also expected that treatment of other less common causes of fetal anemia becomes more frequently reported and that the management principles of fetal anemia are successfully applied to other fetal pathologies.