Evaluation of prenatal RHD typing strategies on cell-free fetal DNA from maternal plasma

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.

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.

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.

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.

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.

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.

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.

Hemolytic disease of the fetus and newborn in the molecular era

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

Performance of Droplet Digital PCR in Non-Invasive Fetal RHD Genotyping - Comparison with a Routine Real-Time PCR Based Approach

Detection and characterization of circulating cell-free fetal DNA (cffDNA) from maternal circulation requires an extremely sensitive and precise method due to very low cffDNA concentration. In our study, droplet digital PCR (ddPCR) was implemented for fetal RHD genotyping from maternal plasma to compare this new quantification alternative with real-time PCR (qPCR) as a golden standard for quantitative analysis of cffDNA. In the first stage of study, a DNA quantification standard was used. Clinical samples, including 10 non-pregnant and 35 pregnant women, were analyzed as a next step. Both methods' performance parameters-standard curve linearity, detection limit and measurement precision-were evaluated. ddPCR in comparison with qPCR has demonstrated sufficient sensitivity for analysing of cffDNA and determination of fetal RhD status from maternal circulation, results of both methods strongly correlated. Despite the more demanding workflow, ddPCR was found to be slightly more precise technology, as evaluated using quantitative standard. Regarding the clinical samples, the precision of both methods equalized with decreasing concentrations of tested DNA samples. In case of cffDNA with very low concentrations, variance parameters of both techniques were comparable. Detected levels of fetal cfDNA in maternal plasma were slightly higher than expected and correlated significantly with gestational age as measured by both methods (ddPCR r = 0.459; qPCR r = 0.438).

How to evaluate PCR assays for the detection of low-level DNA

High sensitivity of PCR-based detection of very low copy number DNA targets is crucial. Much focus has been on design of PCR primers and optimization of the amplification conditions. Very important are also the criteria used for determining the outcome of a PCR assay, e.g. how many replicates are needed and how many of these should be positive or what amount of template should be used? We developed a mathematical model to obtain a simple tool for quick PCR assay evaluation before laboratory optimization and validation procedures. The model was based on the Poisson distribution and the Binomial distribution describing parameters for singleplex real-time PCR-based detection of low-level DNA. The model was tested against experimental data of diluted cell-free foetal DNA. Also, the model was compared with a simplified formula to enable easy predictions. The model predicted outcomes that were not significantly different from experimental data generated by testing of cell-free foetal DNA. Also, the simplified formula was applicable for fast and accurate assay evaluation. In conclusion, the model can be applied for evaluation of sensitivity of real-time PCR-based detection of low-level DNA, and may also assist in design of new assays before standard laboratory optimization and validation is initiated.

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

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

Development and validation of multiplex real-time PCR assay for noninvasive prenatal assessment of fetal RhD status and fetal sex in maternal plasma

OBJECTIVE

Noninvasive prenatal detection of RhD status and fetal sex is becoming part of daily practice in clinical laboratories. We evaluated a high throughput procedure for automated DNA extraction and developed a multiplex real-time PCR (rt-PCR) for the simultaneous detection of three fetal loci in a single reaction to assess fetal sex and RhD status in maternal plasma.

METHODS

An automated DNA extraction method was evaluated together with a new multiplex rt-PCR assay for the simultaneous detection of exons 5 and 7 of the RHD gene together with the Y chromosome marker DYS14 in maternal plasma. The test was evaluated on 60 samples of known fetal genotype obtained from RhD-negative pregnant women before being applied prospectively on 158 consecutive clinical cases. Results were compared with newborn phenotypes.

RESULTS

Automated DNA extraction allowed successful analysis of all samples. DYS14 was detected in 118 cases (male fetuses) and both RHD exon 5 and 7 were detected in 148 samples. In 70 samples neither RHD exon 5 nor RHD exon 7 were detected (RhD-negative fetuses). Absence of all three sequences (female RhD-negative fetuses) was assessed in 33 samples. All prenatal results were in concordance with postnatal RhD status and fetal sex without false- positive or -negative results.

CONCLUSION

The automated DNA extraction procedure coupled with a novel multiplex rt-PCR assay proved accurate, efficient and reliable allowing rapid and high throughput noninvasive determination of fetal sex and RhD status in clinical samples.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Comparison of PCR methods for detecting fetal RhDin maternal plasma

BACKGROUND

Aim of this study was to establish the method yielding the highest sensitivity routinely used to determine fetal RhD type and gender from maternal cell-free plasma DNA in different periods of gestation.

METHODS

Plasma DNA concentrations were measured from 46 pregnant women in different gestational periods and tested for RhD using three different PCR methods on exon 7: Thermal Cycler, Taqman method on LightCycler, and melting curve analysis on LightCycler. In addition, fetal gender was determined by PCR. Cell-free plasma DNA was measured in 100 healthy volunteers as a reference group.

RESULTS

The mean value of cell-free plasma DNA in the reference group was 10.9 pg/microL mean, (standard deviation (SD): 3.66) in 50 healthy women and 12.7 pg/microL (SD: 8.2) in 50 healthy men. In the first trimester of pregnancy cell-free plasma DNA was 14.9 pg/microL mean, (SD: 4.2), in the second trimester 15.4 pg/microL mean, (SD: 4.96), and the maximum was achieved in the third trimester of pregnancy 15.6 pg/microl mean, (SD: 6.49). TaqMan probes had the same accuracy, when compared with Thermal Cycler technology (46 samples, 6 failures). Using real-time PCR with melting curve analysis 12 of 17 samples were correctly tested. Gender determination was correctly in 41 of 46 samples.

CONCLUSION

RhD determinations with TaqMan and Thermal Cycler technology are useful methods for fetal RhD prediction. To increase the accuracy of RhD determination it is necessary to test on other exons in addition.

Non-invasive foetal RHD genotyping via real-time PCR of foetal DNA from Chinese RhD-negative maternal plasma

BACKGROUND

A majority of studies predicting the foetal RhD blood group in free foetal DNA from RhD-negative maternal plasma have been conducted in Caucasian populations, whereas limited data have been accumulated for Asian populations. In this study, we assessed the feasibility of prenatal genotyping of RHD in RhD-negative Chinese pregnant women.

MATERIALS AND METHODS

Cell-free plasma DNA was extracted from 78 RhD-negative Chinese women carrying a singleton foetus (gestation between 14 and 40 weeks). Foetal DNA was confirmed by testing SRY or nine different polymorphic STR loci in the maternal plasma and buffy coat. Foetal RHD exons 5, 7 and 10 and intron 4 were successfully amplified with RQ-PCR. The RHD1227A allele was examined in all RhD-positive individuals. The foetal RHD genotyping results were compared with the infant cord blood serological analysis.

RESULTS

Among the 78 specimens, RHD genotyping results of 70 cases were in complete concordance with serological results from foetal umbilical cord blood. Sixty of these cases were identified as RhD-positive, and 10 cases were typed as RhD-negative. In addition, five cases were 'false-positives', while three cases were considered inconclusive. The detection rate was 89.7% (70/78). In four of the five 'false-positive' cases, the RhDel phenotype was assessed by detecting the RHD1227A allele. Thus, this method yielded a 94.9% (74/78) accuracy rate.

CONCLUSIONS

The correct foetal RhD phenotype may be accurately predicted from RhD-negative maternal plasma in Chinese subjects. The RHD1227A allele proved to be an important genetic marker in the RhDel Chinese population.

Prenatal RhD Testing: A Review of Studies Published from 2006 to 2008

The availability of noninvasive prenatal diagnosis for the fetal RhD status (NIPD RhD) is an obvious benefit for alloimmunized pregnant women. This review gives information about the performance characteristics of current diagnostic technologies and recent promising proof-of-principle studies. Notably, during the past 3 years almost twice as much samples have been investigated with NIPD RhD compared with the studies from 1998 to 2005. Thus we have now a lot more information compared with the knowledge before 2006. There is no doubt that funding of the SAFE Network of Excellence (2004-2009) from the European Commission within the framework 6 program has massively increased the worldwide experience in NIPD RhD. In 2009 European funding has been stopped. Because of this large investment from public funding sources, it is now the duty of policy makers (scientific boards, patient groups, physician organizations, and health assurances) to discuss if targeted antenatal Rh prophylaxis should be introduced in German-speaking countries or which additional data are required to make a decision and how these additional studies should be funded.

The SAFE project: towards non-invasive prenatal diagnosis

After the revolutionary detection of ffDNA (free fetal DNA) in maternal circulation by real-time PCR in 1997 and advances in molecular techniques, NIPD (non-invasive prenatal diagnosis) is now a clinical reality. Non-invasive diagnosis using ffDNA has been implemented, allowing the detection of paternally inherited alleles, sex-linked conditions and some single-gene disorders and is a viable indicator of predisposition to certain obstetric complications [e.g. PET (pre-eclampsia)]. To date, the major use of ffDNA genotyping in the clinic has been for the non-invasive detection of the pregnancies that are at risk of HDFN (haemolytic disease of the fetus and newborn). This has seen numerous clinical services arising across Europe and many large-scale NIPD genotyping studies taking place using maternal plasma. Because of the interest in performing NIPD and the speed at which the research in this area was developing, the SAFE (Special Non-Invasive Advances in Fetal and Neonatal Evaluation) NoE (Network of Excellence) was founded. The SAFE project was set up to implement routine, cost-effective NIPD and neonatal screening through the creation of long-term partnerships within and beyond the European Community and has played a major role in the standardization of non-invasive RHD genotyping. Other research using ffDNA has focused on the amount of ffDNA present in the maternal circulation, with a view to pre-empting various complications of pregnancy. One of the key areas of interest in the non-invasive arena is the prenatal detection of aneuploid pregnancies, particularly Down's syndrome. Owing to the high maternal DNA background, detection of ffDNA from maternal plasma is very difficult; consequently, research in this area is now more focused on ffRNA to produce new biomarkers.

The use of cell-free fetal nucleic acids in maternal blood for non-invasive prenatal diagnosis

BACKGROUND

Cell-free fetal nucleic acids (cffNA) can be detected in the maternal circulation during pregnancy, potentially offering an excellent method for early non-invasive prenatal diagnosis (NIPD) of the genetic status of a fetus. Using molecular techniques, fetal DNA and RNA can be detected from 5 weeks gestation and are rapidly cleared from the circulation following birth.

METHODS

We searched PubMed systematically using keywords free fetal DNA and NIPD. Reference lists from relevant papers were also searched to ensure comprehensive coverage of the area.

RESULTS

Cell-free fetal DNA comprises only 3-6% of the total circulating cell-free DNA, therefore diagnoses are primarily limited to those caused by paternally inherited sequences as well as conditions that can be inferred by the unique gene expression patterns in the fetus and placenta. Broadly, the potential applications of this technology fall into two categories: first, high genetic risk families with inheritable monogenic diseases, including sex determination in cases at risk of X-linked diseases and detection of specific paternally inherited single gene disorders; and second, routine antenatal care offered to all pregnant women, including prenatal screening/diagnosis for aneuploidy, particularly Down syndrome (DS), and diagnosis of Rhesus factor status in RhD negative women. Already sex determination and Rhesus factor diagnosis are nearing translation into clinical practice for high-risk individuals.

CONCLUSIONS

The analysis of cffNA may allow NIPD for a variety of genetic conditions and may in future form part of national antenatal screening programmes for DS and other common genetic disorders.

Ultrastructural localization of glycoprotein IIIa (GPIIIa, beta 3 integrin) on placental syncytiotrophoblast microvilli: implications for platelet alloimmunization during pregnancy

BACKGROUND

Fetal and neonatal alloimmune thrombocytopenia due to anti-human platelet antigen (HPA)-1a more commonly occurs in first pregnancies, unlike hemolytic disease of the newborn. Anti-D is produced after D+ fetomaternal hemorrhage; this usually occurs at parturition. Anti-HPA-1a could develop during pregnancy if maternal immunization is stimulated by HPA-1a expressed not only on platelets but also on other fetal cells.

STUDY DESIGN AND METHODS

An ultrastructural study of fetal placental chorionic villi was undertaken to determine the localization of glycoprotein (GP)IIIa carrying the HPA-1a/1b polymorphism. First trimester and term villi were incubated with a monoclonal antibody (MoAb) to GPIIIa or with positive control MoAbs (anti-placental alkaline phosphatase and ED822 MoAb) to villous syncytiotrophoblast (ST). Binding of MoAbs was detected with a gold-conjugated secondary antibody before processing the tissues and examination of ultrathin sections in an electron microscope.

RESULTS

Gold particles were evident on microvilli on the apical surface of ST when labeled with anti-GPIIIa and the placenta-specific MoAbs but not with an isotype control antibody. Immunolabeling for anti-GPIIIa on first trimester ST was similar to that of term ST.

CONCLUSION

The apical surface of the ST is bathed in maternal blood. During the natural regenerative process of human placenta, senescent parts of the ST are shed into maternal blood during pregnancy. This includes both apoptotic ST nuclei and microparticulate ST debris. The presence of GPIIIa on this circulating ST cellular material could be the source of HPA-1a alloantigen causing primary immunization of susceptible primigravidae early enough for anti-HPA-1a to cause fetal thrombocytopenia during a first pregnancy.

Non-invasive prenatal diagnosis and determination of fetal Rh status

RhD blood group incompatibility between a pregnant woman and her fetus can result in maternal alloimmunization and consequent haemolytic disease of the newborn (HDN) in subsequent pregnancies. The D-negative blood group is found in 15% of whites, 3-5% of black Africans, and is rare in Asians. Recent technological advances in non-invasive prenatal determination of the fetal RHD status using cell-free fetal DNA (cffDNA) have opened new avenues for the management of D-negative pregnant women. In this review applications for the high risk women, as well as potential for routine screening will be discussed. The use of non-invasive prenatal diagnosis and the management of other blood incompatibilities will also be discussed.

Noninvasive fetal RHD genotyping from maternal plasma. Use of a new developed Free DNA Fetal Kit RhD

Fetal RHD genotyping from maternal plasma was performed by real-time PCR amplification of exons 7 and 10 of the RHD gene and the amplified products were detected either with SYBR Green I dye according to our previously published method [Mol Diagn 8 (2004) 23-31] or with hydrolysis probes in a new Free DNA Fetal Kit RhD((R)). Plasma specimen from 300 RhD-negative pregnant women (between 10 to 34 weeks of gestation) were analysed and validation of the results was ascertained either by RHD genotyping on amniotic cells or by blood typing of the neonate at birth. We found 100% concordant results when comparing the two methods. Two false-positive but no false-negative results were found. Thus, the sensitivity of the assay was 100% and the specificity superior than 99%. These data confirm the accuracy of fetal RHD genotyping on maternal plasma using the Free DNA Fetal Kit RhD, thus allowing to propose non invasive PCR-based fetal RHD genotyping for all RhD-negative pregnant women and to restrict the use of anti-D immunoglobulins only to those bearing an RhD-positive fetus.

Routine fetal RHD genotyping with maternal plasma: a four-year experience in Belgium

BACKGROUND

The objective was to evaluate the diagnostic value of RHD fetal genotyping from the plasma of D- mothers as soon as 10 weeks' gestation in a routine clinical practice in Belgium.

STUDY DESIGN AND METHODS

A prospective study was conducted between November 2002 and December 2006. DNA extraction was performed in an automated closed tube system. Fetal RHD/SRY genotypes were detected in the plasma of 563 pregnant mothers by real-time polymerase chain reaction (PCR) targeting multiple exons 4, 5, and 10 of the RHD gene and targeting an SRY gene sequence. These were compared to the D phenotypes determined in the 581 babies they delivered.

RESULTS

By combining amplification of three exons, the concordance rate of fetal RHD genotypes in maternal plasma and newborn D phenotypes at delivery was 100 percent (99.8% including one unusual false-positive). The presence of nonfunctional RHD genes and the absence of a universal fetal marker, irrespective of fetal sex, did not influence the accuracy of fetal RhD status prediction. The RHD genotyping from 18 twin pregnancies was also assessed. Five weak D women were excluded from the RHD fetal genotyping prediction. Three discrepant results (0.5%) between predicted fetal genotype and cord blood phenotype were not confirmed by the baby phenotypes from venipuncture blood.

CONCLUSION

Prenatal prediction of fetal RHD by targeting multiple exons from the maternal plasma with real-time PCR is highly sensitive and accurate. Over 4 years, this experience has highly modified our management of D- pregnant women.

Blood group genotyping in Germany

BACKGROUND

Molecular methods for blood group genotyping became available more than 10 years ago as one major aspect of immunogenetics. Since then, the clinical applications have been expanded and refined. Their implementation varies considerably among different health-care systems, notably between North America and Europe.

STUDY DESIGN

This summary is based on studies published mostly during the last 3 years and on workshop reports from the German and Swiss transfusion societies. It represents an edited transcript of the author's presentation given at the Workshop on Molecular Methods in Immunohematology organized by the Food and Drug Administration (FDA) in Bethesda on September 25, 2006.

RESULTS

Current applications of blood group genotyping in Germany, Switzerland, and Austria are detailed: weak D testing in patients and pregnant women; blood group genotyping in perinatal care, in patients who received a transfusion, and in patients with immunohematologic problems; RHD genotyping in donors for DEL and D(+/-) chimera; and RHD zygosity testing.

CONCLUSION

Since around 2000, molecular tests for blood groups have been widely offered as a routine service. Many samples are shipped to reference laboratories in the German-speaking countries with the specific request for such testing. The advent of Conformité Européenne (CE)-labeled test kits renders it technically and legally possible, within the specifications of the CE-certification process for in vitro diagnostic devices in the European Union, to replace several blood group serology tasks by genotyping.

Fetal blood group genotyping

Blood group genotyping using DNA extracted from fetal tissue is useful to identify fetuses at risk for hemolytic disease of the fetus and newborn (HDFN) due to maternal red cell alloantibodies. Four considerations are important for fetal blood group genotyping. First, paternal heterozygosity must be established, including tests that evaluate RHD hemizygosity. Second, the source of fetal tissue for DNA extraction requires certain considerations. Third, because the fetal genotype is used to predict the expressed phenotype, a thorough knowledge of blood group genetics is required. Moreover, the test algorithm should include the evaluation of the parental phenotypes and genotypes to help identify variant alleles. Fourth, the blood group antigen expression at birth should be evaluated to confirm the inheritance. The identification of an antigen-negative fetus on the basis of the blood group genotype provides significant advantages in managing the pregnancy at risk for HDFN. In the near future, fetal DNA in maternal plasma will likely replace fetal blood group genotyping for RHD. Significant challenges remain to detect other clinically significant blood group antigens using maternal plasma DNA.