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

Next generation sequencing based approach for fetal DNA quantification and blood antigen detection in alloimmunized pregnancies

BACKGROUND

Erythrocyte and platelet alloimmunization during pregnancy can be severe and are closely monitored through the pregnancy, however, the blood type of the fetus and associated risk are often unknown. In this study, we determined the fetal erythrocyte and platelet genotype from maternal plasma using next generation sequencing (NGS), providing a non-invasive testing (NIPT) as an alternative to traditional methods for monitoring alloimmunized pregnancies.

OBJECTIVES

This study aims to validate an innovative NGS method for detection of specific blood antigens in maternal plasma-derived cell-free DNA, focusing on key antigens associated with immunizations. By analyzing free-circulating fetal DNA across various gestational stages, the study seeks to achieve high-precision identification of clinically relevant erythrocyte and platelet antigens.

STUDY DESIGN

Maternal whole blood samples were consecutively collected from 74 both immunized and non-immunized pregnant women at 13-27 gestation week in the Stockholm County, Sweden. NGS analysis was performed on maternal plasma using a prototype kit from Devyser AB (Stockholm, Sweden). The kit detects several erythrocyte blood group markers, two human platelet antigen markers (HPA-1 and HPA-5), XY-chromosome markers, and 12 insertions and deletions (Indels) from different chromosomes to identify and quantify fetal DNA. Post-birth, genomic DNA from umbilical cord blood samples were genotyped with various methods and compared to NIPT results obtained during pregnancy.

RESULTS

A total of 95 samples from 74 pregnancies were analyzed. Fetal DNA was successfully identified in 72 out of 74 cases (97.3%) using Indel and Y-chromosome markers. In two cases, fetal DNA could not be detected due to the absence of informative markers. The NIPT results showed 100% concordance with the genotyped newborns. Among the 22 immunized women, six of the fetuses were antigen-negative, ten were antigen-positive, five had antigens not included in the NGS panel (three anti-Cw, one anti-M, and one anti-Ge2), and one result was inconclusive.

CONCLUSION

This study highlights the feasibility of using NGS for comprehensive fetal antigen screening, paving the way for a personalized approach to managing alloimmunized pregnancies. By accurately identifying fetuses expressing antigens corresponding to maternal antibodies, and those not at risk, it enhances the precision of targeted care.

Potential of a Second Screening Test for Alloimmunization in Pregnancies of Rhesus-positive Women: A Swedish Population-based Cohort Study

INTRODUCTION

There is lack of consensus regarding whether a second screening in rhesus-positive pregnant women is worthwhile, with different guidelines, recommendations, and practices. We aimed to estimate the number and timing of missed alloimmunizations in rhesus-positive pregnancies screened once and weigh the relative burden of additional screening and monitoring versus the estimated reduction in adverse pregnancy outcomes.

METHODS

We extracted information on maternal, pregnancy, and screening results for 682,126 pregnancies for 2003-2012 from Swedish national registers. We used data from counties with a routine second screening to develop and validate a logistic model for a positive second test after an earlier negative. We used this model to predict the number of missed alloimmunizations in counties offering only one screening. Interval-censored survival analysis identified an optimal time window for a second test. We compared the burden of additional screening with estimated adverse pregnancy outcomes avoided.

RESULTS

The model provided an accurate estimate of positive tests at the second screening. For counties with the lowest screening rates, we estimated that a second screening would increase the alloimmunization prevalence by 33% (from 0.19% to 0.25%), detecting the 25% (304/1222) of cases that are currently missed. The suggested timing of a second screen was gestational week 28. For pregnancies currently screened once, the estimated cost of a second test followed by maternal monitoring was approximately 10% of the cost incurred by the excess adverse pregnancy outcomes.

CONCLUSION

Investment in routine second screening can identify many alloimmunizations that currently go undetected or are detected late, with the potential for cost savings.

Antenatal anti-D prophylaxis and D antigen negativity in pregnant women of the UAE: a cross-sectional analysis from the Mutaba'ah Study

OBJECTIVE

This study aimed to determine the prevalence of the negative D antigen phenotype, adherence to routine antenatal anti-D immunoglobulin prophylaxis (RAADP) administration and D antigen sensitisation among pregnant women in the UAE.

DESIGN

Data was collected from pregnant women enrolled in the Mutaba'ah Study. The Mutaba'ah Study is an ongoing prospective mother and child cohort study in the UAE. Data were extracted from the medical records and baseline questionnaire administered to the participants between May 2017 and January 2021.

SETTING

The study was conducted in Al Ain city of the UAE.

PARTICIPANTS

A total of 5080 pregnant women residing in Al Ain participated in the study.

OUTCOME MEASURES

The study estimated the prevalence of negative D antigen phenotype and the provision of RAADP in this population.

RESULTS

Of the 5080 pregnant women analysed, 4651 (91.6%) had D antigen positive status, while 429 (8.4%) were D-negative. D antigen sensitisation was low at 0.5%, and there was a high uptake of RAADP in the population at 88.8%.

CONCLUSIONS

The adherence to RAADP is consistent with published data from other healthcare settings. Knowledge of the prevalence of D antigen negative mothers is crucial to the financial and resource consideration for implementing antenatal foetal cell-free DNA screening to determine foetal D antigen status.

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.

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.

Single-exon approach to non-invasive fetal RHD screening in early pregnancy: An update after 10 years' experience

BACKGROUND AND OBJECTIVES

Anti-D prophylaxis, administered to RhD-negative women, has significantly reduced the incidence of RhD immunization. Non-invasive fetal RHD screening has been used in Stockholm for more than 10 years to identify women who will benefit from prophylaxis. The method is based on a single-exon approach and is used in early pregnancy. The aim of this study was to update the performance of the method.

MATERIALS AND METHODS

The single exon assay from Devyser AB is a multiplex kit detecting both exon 4 of the RHD gene and the housekeeping gene GAPDH. Cell-free DNA was extracted from 1 ml of plasma from EDTA blood taken during early pregnancy, weeks 10-12. The genetic RHD results were compared with serological typing of newborns for a determination of sensitivity and specificity.

RESULTS

In total, 4337 pregnancies were included in the study; 44 samples (1%) were inconclusive either due to maternal RHD gene variants (n = 34) or technical reasons (n = 10). Of the remaining 4293 pregnancies, a total number of nine discrepant results were found. False positive results (n = 7) were mainly (n = 4) due to RHD gene variants in the child. False-negative results were found in two cases, of which one was caused by a technical error. None of the false-negative cases was due to RHD gene variants. Overall, the sensitivity of the method was 99.93% and specificity 99.56%.

CONCLUSION

The single-exon assay used in this study is correlated with high sensitivity and specificity.

Noninvasive Prenatal Testing in Immunohematology-Clinical, Technical and Ethical Considerations

Hemolytic disease of the fetus and newborn (HDFN), as well as fetal and neonatal alloimmune thrombocytopenia (FNAIT), represent two important disease entities that are caused by maternal IgG antibodies directed against nonmaternally inherited antigens on the fetal blood cells. These antibodies are most frequently directed against the RhD antigen on red blood cells (RBCs) or the human platelet antigen 1a (HPA-1a) on platelets. For optimal management of pregnancies where HDFN or FNAIT is suspected, it is essential to determine the RhD or the HPA-1a type of the fetus. Noninvasive fetal RhD typing is also relevant for identifying which RhD-negative pregnant women should receive antenatal RhD prophylaxis. In this review, we will give an overview of the clinical indications and technical challenges related to the noninvasive analysis of fetal RBCs or platelet types. In addition, we will discuss the ethical implications associated with the routine administration of antenatal RhD to all pregnant RhD-negative women and likewise the ethical challenges related to making clinical decisions concerning the mother that have been based on samples collected from the (presumptive) father, which is a common practice when determining the risk of FNAIT.

Nichtinvasiver Pränataltest zur Bestimmung des fetalen Rhesusfaktors

Seit dem 01.07.2021 soll in Deutschland die präpartale Anti-D-Prophylaxe in Abhängigkeit vom Ergebnis des nichtinvasiven Pränataltests zur Bestimmung des fetalen Rhesusfaktors (NIPT-RhD) verabreicht werden. In der Praxis ergeben sich gelegentlich Fragen zur Bewertung der Testergebnisse, die auf die Komplexität des Rhesus-Blutgruppensystems zurückzuführen sind. Antworten auf diese und andere Fragen zum NIPT-RhD gibt dieser Beitrag.

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.

RHD Genotypes in a Chinese Cohort of Pregnant Women

RHD variants in D¯ Chinese pregnant women arose difficulties in management during pregnancy. Therefore, this study aims to precisely manage D¯ pregnant women by evaluating the spectrum of RHD mutations in D¯ pregnant women and getting insight into the possible rare alleles of RHD. A total of 76 D¯ pregnant women were analyzed by performing polymerase chain reactions with sequence-specific primers (PCR-SSP), the 10 RHD exons Sanger sequencing, RHD zygosity detection, and mRNA sequencing (mRNA-seq). About 40% of alleles are variations of RHD, including RHD 1227A homozygous, RHD-CE(2-9)-D, et al. Therefore, we developed a molecular diagnostic strategy for Chinese women, and most D¯ pregnant women can be diagnosed with this simple decision tree. After RHD genotyping for D¯ pregnancy women, we eliminated at least 15% unnecessary ante- and postpartum injections of Rh immunoglobulin (RhIG). As the first pedigree study and the first functional analysis under physiological conditions, mRNA-seq revealed that c.336-1G>A mutation mainly led to the inclusion of the intron 2, which indirectly explained the D¯ phenotype in this family. We also developed a robust protocol for determining fetal RhD status from maternal plasma. All 31 fetuses were predicted as RhD positive and confirmed the RhD status after birth.

Management and clinical consequences of red blood cell antibodies in pregnancy: A population-based cohort study

INTRODUCTION

Anti-D alloimmunization is the most common cause of severe hemolytic disease of the fetus and newborn (HDFN). The management of pregnancies affected by less frequent red blood cell (RBC) antibodies poses a challenge to clinicians, and perinatal outcomes are less well described. This study aimed to describe the frequency of clinically significant RBC antibodies in our pregnant population and analyze the risk of prenatal and postnatal treatment for HDFN in relation to our national risk classification system and management guidelines.

MATERIAL AND METHODS

A retrospective cohort study in the population of all alloimmunized singleton pregnancies in the Stockholm region 1990-2016. Descriptive summaries of different RBC antibodies and pregnancy outcomes were presented, the risks of intrauterine blood transfusion (IUT) and neonatal treatment for HDFN were estimated by type of antibodies.

RESULTS

Of the 1724 alloimmunized pregnancies, 1079 (63%) were at risk of HDFN and constituted our study cohort. Anti-D was detected in 492 (46%) pregnancies, followed by anti-E in 161 (15%), and anti-c in 128 (12%). Eighty-seven (8%) pregnancies had IUT, with the highest risk in pregnancies affected by anti-D combined with other antibodies. The maximum titer recorded before IUT was 64 or above, except for two pregnancies affected by anti-c, for which the maximum titers were 8 and 16. For the 942 (95%) live-born neonates from 992 alloimmunized pregnancies without IUT, the median gestational age at birth was 38⁺⁵  weeks compared with 35⁺⁵  weeks for those who had IUT. Neonatal treatment was most common in the anti-D alone and anti-D combined groups, with 136 (57%) and 21 (44%), respectively, treated with phototherapy and 35 (15%) and 9 (20%) receiving exchange transfusions, respectively. For pregnancies complicated by moderate- and low-risk antibodies, phototherapy was less frequent (32 [36%] and 21 [19%]) and exchange transfusion was rare (5 [6%] and 3 [3%]).

CONCLUSIONS

Anti-D, especially in combination with other antibodies, presents the highest risk of severe HDFN. The classification of less frequent and less well-known RBC antibodies into risk groups can help clinicians in assessing the risk of HDFN and counseling alloimmunized pregnant women regarding the risk of prenatal and postnatal treatments.

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.

Altered strategy of prophylactic anti-D administration in pregnancy to cover term and post-term - a pilot study

BACKGROUND AND OBJECTIVE

Routine antenatal anti-D prophylaxis (RAADP) to RhD-negative women is most often administered in gestational age (GA) 28-30 weeks with the next anti-D dose administered postpartum. The aim of this study was to analyse the proportion of RhD-negative women where RAADP is not detectable at term and in a pilot study to investigate whether RAADP administered in GA 28 and 38 results in detectable levels at term, post-term and post-delivery.

MATERIALS AND METHODS

In a retrospective analysis, 4280 RhD-negative women carrying an RHD positive fetus were included and the proportion with a negative antibody screen at delivery was determined. In the second part, 39 pregnancies were included prospectively, a second dose of RAADP was administered in GA 38 weeks, and anti-D was quantified before the second dose and then weekly for 5 weeks.

RESULTS

In the retrospective analysis, 20·5% (856/4280) with RAADP administered in GA 28 were negative in routine antibody screening at delivery. In the small prospective study, 18% (7/39) had a negative antibody screen and 26% (10/39) had levels below 0·005 IU/ml, in the quantification assay, in GA 38. Anti-D prophylaxis administered in GA 38 showed detectable levels of anti-D up to 30 days post-delivery, with concentration at delivery 0·060 ± 0·034 IU/ml (mean ± SD).

CONCLUSION

Approximately 20% of the RhD-negative women show non-detectable levels of anti-D at term. A second dose of RAADP at GA 38 results in stable concentrations of anti-D at term, post-term and post-delivery, but with large interindividual variation.

Optimization of diagnostic strategy for non-invasive cell-free foetal RHD determination from maternal plasma

BACKGROUND AND OBJECTIVES

The aim of the study was to optimize routine non-invasive prenatal detection of fetal RHD gene from plasma of RhD-negative pregnant women (the median of gestational age was 25 weeks, range 10-38) to detect RhD materno-fetal incompatibility and to avoid the redundant immunoprophylaxis.

MATERIALS AND METHODS

Initially only one exon of RHD gene (exon 10) was investigated in 281 plasma samples (144 verified after delivery), in the second phase three RHD exons (5, 7, 10) were analyzed in 246 samples of plasma and maternal genomic DNA (204 verified) by real-time PCR method. Detection of Y-chromosomal sequence DYS-14 and five X-chromosomal insertion/deletion polymorphisms was used to confirm the fetal cfDNA detectability in plasma. Specific polymorphisms in RHD gene were detected by sequence-specific primer PCR in nine samples.

RESULTS

When only the RHD exon 10 was tested, 2·8% of verified samples were false positive and 3·5% false negative. With three RHD exons (5, 7, 10) and maternal genomic DNA testing, only one case was false negative (0·5%). Nine samples were inconclusive due to RHD-positive results in maternal genomic DNA. These samples were analyzed for specific mutations in RHD gene. Combination of both methods for fetal cfDNA verification succeeded in 75% of tested group.

CONCLUSION

Implementation of analysis of three RHD exons and maternal genomic DNA to routine practice lowers dramatically the ratio of false positive and negative results. This method enables more accurate determination of fetal RHD status with the reduction of unnecessary medical care and RhD immunoprophylaxis.

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.

Fetal Rhesus D Genotyping and Sex Determination from Maternal Plasma of Rhesus D-Negative Antenatal Population: The Usefulness of Conventional Polymerase Chain Reaction in Resource-limited Settings

Background

This prospective cohort study evaluated the usefulness of conventional PCR in genotyping fetal Rhesus D (RhD) and sex from the maternal plasma of RhD-negative (RhD−) antenatal population in resource-limited settings.

Methods

Thirty apparently healthy RhD− pregnant women with RhD positive (RhD+) partners were included. Blood samples were collected from each participant (in the third trimester of pregnancy) for DNA extraction/purification and fetal RhD genotyping.

Results

Out of the 30 samples, 26 (86.7%) were found to be RhD+ while 4 (13.3%) were RhD−. The RhD+ comprised 24 (80.0%) RhD+ based on exons 5, 7, and 10 combined. Exons 5 and 7 were detected in two additional samples but not exon 10. Serological phenotyping of neonatal blood confirmed 26 RhD+ and 4 RhD−. There was a perfect agreement between the fetal RhD genotype and neonatal RhD phenotyping after delivery for exons 5 and 7 (concordance = 100%, κ = 100.0%, diagnostic accuracy = 100%, p < 0.0001) while exon 10 presented with an almost perfect agreement (concordance = 93.3%, κ = 76.2%, diagnostic accuracy = 93.3%, p < 0.0001). Regarding the prenatal test for the SRY gene, 9 (30.0%) were predicted to be males and the remaining 21 (60.0%) were females. All the 9 and 21 anticipated males and females, respectively, were confirmed after delivery (concordance = 100%, κ = 100.0%, diagnostic accuracy = 100%).

Conclusion

Our study suggests that conventional PCR using the SRY, RhD exons 5 and 7 could be useful for predicting fetal sex and RhD from maternal peripheral blood in resource-limited settings.

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.

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.

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

Background

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

Objectives

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

Methods

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

Results

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

Conclusion

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

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

Background

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

Methods

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

Results

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

Conclusions

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

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

LIMITATIONS

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

CONCLUSIONS

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

FUTURE WORK

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

STUDY REGISTRATION

This study is registered as PROSPERO CRD42015029497.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Targeted Rhesus immunoglobulin for RhD-negative women undergoing an induced abortion: A clinical pilot study

INTRODUCTION

The aim of this clinical pilot study was to examine the accuracy of noninvasive fetal RHD genotyping in early pregnancy (8⁺⁰  to 11⁺⁶  weeks) and to clarify whether targeted administration of Rhesus immunoglobulin (RhIg) is possible for women undergoing an induced abortion such that unnecessary injections can be avoided. The study examines the correlation between gestational age and the amount of cell-free fetal DNA in maternal plasma, the fetal fraction of DNA and whether transportation time or body mass index affects these parameters.

MATERIAL AND METHODS

Fifty-two RhD-negative women undergoing a surgically induced abortion were included. A maternal blood sample was collected prior to the abortion and a tissue sample was collected from the placental part of the abortion material after the intervention. Fetal RhD type was determined by PCR analysis of cell-free fetal DNA extracted from maternal plasma and on DNA from the tissue sample, with the latter providing a reference standard. Copies of RHD/mL were determined on RHD-positive samples and the fetal fraction of DNA was calculated.

RESULTS

We demonstrated complete concordance between results from plasma and tissue, with 31 RhD-positive and 21 RhD-negative samples, corresponding to 40% being RhD-negative, specificity 100% [95% confidence interval (CI) 88.8-100] and sensitivity 100% (95% CI 83.9-100). We found no significant correlation between gestational age and the amount or the fraction of cell-free fetal DNA in maternal plasma, nor did we find that transportation time or BMI significantly affected these factors in this setup.

CONCLUSIONS

Fetal RHD genotyping can be accurately performed from the 8th week of gestation and unnecessary injections of RhIg can be avoided for women undergoing an induced abortion. A larger study is needed to determine a more accurate sensitivity for the analysis early in pregnancy.

Blood group genotyping

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effectiveness and costs of non-invasive foetal RHD genotyping in rhesus-D negative mothers: a French multicentric two-arm study of 850 women

Background

The determination of foetal Rhesus D (RHD) status allows appropriate use of IgRh prophylaxis by restricting its use to cases of RHD feto-maternal incompatibilities. There is a degree of uncertainty about the cost-effectiveness of foetal RHD determination, yet screening programs are being introduced into clinical practice in many countries.

This paper evaluates the impact of non-invasive foetal Rhesus D (RHD) status determination on the costs of managing RHD-negative pregnant women and on the appropriate use of anti-D prophylaxis in a large sample of RHD-negative pregnant women using individual prospectively collected clinical and economic data.

Methods

A prospective two-armed trial of RHD negative pregnant women was performed in 11 French Obstetric Departments. Non-invasive foetal RHD genotyping was performed before 26 weeks' gestation in the experimental arm whereas the control arm participants received usual care. The costs associated with patient management in relation to their RHD negative status (biological tests, anti-D prophylaxis and visits) were calculated from inclusion to the end of the postpartum period. The costs of hospital admissions during pregnancy and delivery were also determined.

Results

A total of 949 patients were included by 11 centres between 2009 and 2012, and 850 completed follow-up, including medical and biological monitoring. Patients were separated into two groups: the genotyping group (n=515) and the control group (n=335). The cost of the genotyping was estimated at 140 euros per test. The total mean cost per patient was estimated at €3,259 (SD ± 1,120) and €3,004 (SD ± 1,004) in the genotyping and control groups respectively. The cost of delivery represented three quarters of the total cost in both groups. The performance of managing appropriately RHD negative anti-D prophylaxis was 88% in the genotyping group, versus 65% in the control group. Using the costs related to RHD status (biological tests, anti-D immunoglobulin injections and visits) the incremental cost-effectiveness ratio (ICER) was calculated to be €578 for each percentage gain in women receiving appropriate management.

Conclusion

Early knowledge of the RHD status of the foetus using non-invasive foetal RHD genotyping significantly improved the management of RHD negative pregnancies with a small increase in cost.

Trial registration

Clinical trials registry-NCT00832962–13 January 2009 - retrospectively registered.

Electronic supplementary material

The online version of this article (10.1186/s12884-018-2114-5) contains supplementary material, which is available to authorized users.

Anti-D quantification in relation to anti-D titre, middle cerebral artery Doppler measurement and clinical outcome in RhD-immunized pregnancies

BACKGROUND

The optimal strategy to monitor RhD-immunized pregnancies is not evident. Whether a quantitative analysis of anti-D antibodies adds valuable information to anti-D titre is unclear. The aim of this study was to evaluate the relevance of anti-D quantification in routine monitoring of RhD-immunized pregnancies.

MATERIALS AND METHODS

In a retrospective study, 64 consecutive pregnancies in 61 immunized women with anti-D titre ≥128 at any time during pregnancy were included. According to routine, at titre ≥128, anti-D quantification was performed by flow cytometry and the peak systolic velocity in the middle cerebral artery was measured by ultrasound. Decisions for treatment with intrauterine blood transfusion were based on increased peak systolic velocity in the middle cerebral artery.

RESULTS

Increasing anti-D concentrations correlated well to increasing anti-D titres, but at each titre value, there was a large interindividual variation, in the determined anti-D concentration. Intrauterine transfusions were initiated in 35 pregnancies according to algorithms based on ultrasound measurements, at anti-D concentrations of 2·4-619 IU/ml and titre 128-16 000. Sixty pregnancies resulted in a live-born child, three in miscarriage and one in termination of pregnancy. During the perinatal care in the neonatal intensive care unit, thirty-one of the neonates were treated with blood exchange transfusions and/or red cell transfusions and 47 were treated with phototherapy.

CONCLUSION

Anti-D quantification does not add further information compared to anti-D titre, in defining a critical level to start monitoring RhD-immunized pregnancies with Doppler ultrasound.

Admission cardiotocography: A hospital based validation study

OBJECTIVE

Admission CTG is a short fetal heart rate (FHR) tracing recorded immediately at hospital admission to avoid unnecessary delay in action among pregnancies complicated by pre-existent fetal distress. There are different opinions regarding the value of the admission CTG, especially in low risk pregnancies.

STUDY DESIGN

A retrospective validation study from Karolinska University Hospital, Jan 2011 to June 2015 (total number of deliveries = 40,061). All women who underwent emergency cesarean section within one hour of admittance due to suspected fetal distress were identified. We assessed whether an admission CTG was performed, if it was beneficial for the decision to perform emergent cesarean delivery and if there were objective signs of fetal compromise or if it was performed unnecessarily. The main outcome was the benefit of the admission CTG in the decision to perform emergency cesarean delivery.

RESULTS

Eighty-eight cases (0.22%) fulfilled our inclusion criteria. Over 90% of these women (80/88) had objective evidence of compromised fetal well-being, i.e., indicating that emergent delivery was necessary. In 74% (54/73) of all cases was admission CTG determined to have been beneficial in the decision to perform cesarean delivery, equally effective of those classified as low- and high risk pregnancies before admission. In 28% (15/54) the CTG pathology was deemed difficult to identify by auscultation.

CONCLUSION

Admission CTG was deemed beneficial in 74% of both low- and high-risk pregnancies that were delivered by emergent cesarean section within one hour of admittance due to suspected fetal distress.

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

BACKGROUND

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

MATERIAL AND METHODS

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

RESULTS

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

DISCUSSION

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

Evaluation of a Decision Tree for Efficient Antenatal Red Blood Cell Antibody Screening

BACKGROUND

Hemolytic disease of the fetus and newborn due to maternal red blood cell alloimmunization can have serious consequences. Because early detection enables careful monitoring of affected pregnancies, programs to routinely screen all pregnant women have been widely adopted. Due to the low prevalence of alloimmunization, these require large investments of resources to detect a small number of cases.

METHODS

We conducted a validation study of a decision tree developed in the Netherlands for determining whether to screen for alloimmunization. In a Swedish cohort, we compared the performance of that decision tree to two alternative models that used maternal characteristics, obstetric history, and transfusion history to identify high-risk women for screening or low-risk women who might be exempt from screening. The models were compared for predictive ability and potential reduction in the volume of screening.

RESULTS

The decision tree applied to our study population identified 89% of alloimmunized women with a negative predictive value (NPV) of 99.7% by screening 62% of the population. To achieve the same NPV, our model exempting low-risk women captured 90% of alloimmunizations by screening 63% of the population. In contrast, the model identifying high-risk women for screening while maintaining a similar NPV captured 63% of alloimmunized women by screening 20% of the population.

CONCLUSIONS

We validated that an existing decision tree for selecting women for maternal screening performed well in our population, identifying a large proportion of women who became alloimmunized, with a predictive performance almost identical to that of a more elaborate model.

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

OBJECTIVE

 To determine the accuracy of non-invasive fetal testing for the RHD gene in week 27 of pregnancy as part of an antenatal screening programme to restrict anti-D immunoglobulin use to women carrying a child positive for RHD DESIGN:  Prospectively monitoring of fetal RHD testing accuracy compared with serological cord blood typing on introduction of the test. Fetal RHD testing was performed with a duplex real time quantitative polymerase chain reaction, with cell-free fetal DNA isolated from 1 mL of maternal plasma The study period was between 4 July 2011 and 7 October 2012. The proportion of women participating in screening was determined.

SETTING

 Nationwide screening programme, the Netherlands. Tests are performed in a centralised setting.

PARTICIPANTS

 25 789 RhD negative pregnant women.

MAIN OUTCOME MEASURES

 Sensitivity, specificity, false negative rate, and false positive rate of fetal RHD testing compared with serological cord blood typing; proportion of technical failures; and compliance to the screening programme.

RESULTS

 A fetal RHD test result and serological cord blood result were available for 25 789 pregnancies. Sensitivity for detection of fetal RHD was 99.94% (95% confidence interval 99.89% to 99.97%) and specificity was 97.74% (97.43% to 98.02%). Nine false negative results for fetal RHD testing were registered (0.03%, 95% confidence interval 0.01% to 0.06%). In two cases these were due to technical failures. False positive fetal RHD testing results were registered for 225 samples (0.87%, 0.76% to 0.99%). Weak RhD expression was shown in 22 of these cases, justifying anti-D immunoglobulin use. The negative and positive predictive values were 99.91% (95% confidence interval 99.82% to 99.95%) and 98.60% (98.40% to 98.77%), respectively. More than 98% of the women participated in the screening programme.

CONCLUSIONS

 Fetal RHD testing in week 27 of pregnancy as part of a national antenatal screening programme is highly reliable and can be used to target both antenatal and postnatal anti-D immunoglobulin use.

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

BACKGROUND

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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