The use of maternal plasma for prenatal RhD blood group genotyping

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.

Noninvasive screening of fetal RHD genotype in Chinese pregnant women with serologic RhD-negative phenotype

BACKGROUND

Noninvasive fetal RHD genotyping has been provided to nonimmunized RhD-negative pregnant women to guide anti-D prophylaxis. Among the Chinese, more than 30% of the RhD-negative phenotype is associated with variant RHD alleles, which would limit the accuracy of fetal RHD status prediction; thus, more targeting and proper programs need to be developed.

STUDY DESIGN AND METHODS

Fluorescence quantitative polymerase chain reaction PCR (qPCR) or Sanger sequencing on all RHD exons was used to detect maternal RHD genotypes. For pregnant women with RHD*01N.01 or RHD*01N.03 alleles, the presence of RHD exons 5 and 10 in cell-free DNA was determined by qPCR. For pregnant women with the RHD(1227G>A) allele, high-throughput sequencing on exon 9 of the RHD gene and RHCE gene was used to predict fetal RhD phenotype.

RESULTS

Among 65 cases of Chinese pregnant women with the serologic RhD-negative phenotype, three major genotypes were identified: RHD*01N.01/RHD*01N.01 (61.5%), RHD*01N.01/RHD(1227G>A) or RHD*01N.03/RHD(1227G>A) (20%), and RHD*01N.01/RHD*01N.03 (13.8%), along with three cases of minor genotypes (4.6%). For 43 pregnant women with the RHD*01N.01 or RHD*01N.03 alleles, qPCR on maternal cell-free DNA yielded a 98.5% (42/43) accuracy rate and 100% successful prediction rate. High-throughput sequencing was successfully used to predict fetal RhD phenotypes for 13 pregnant women with RHD(1227G>A).

CONCLUSION

On the basis of maternal RHD genotyping, fetal genotyping through qPCR or high-throughput sequencing can improve the accuracy and success rate of prenatal fetal RhD phenotype prediction among Chinese pregnant women. It plays a potential role in guiding anti-D prophylaxis and pregnancy management in Chinese pregnant women.

High Levels of CXCL8 and Low Levels of CXCL9 and CXCL10 in Women with Maternal RhD Alloimmunization

Maternal RhD alloimmunization is an inflammatory response against protein antigens in fetal red blood cells (RBC). However, not all women become alloimmunized when exposed to RhD⁺ fetal RBC. Thus, this study aimed to evaluate levels of inflammatory chemokines in RhD⁻ pregnant women with erythrocyte alloimmunization. CXCL8, CXCL9, CCL5, and CXCL10 levels were determined from cell culture supernatants by flow cytometry in 46 (30 non-alloimmunized RhD⁻ and 16 previously alloimmunized RhD⁻) pregnant women. CXCL8 levels were significantly higher (P < 0.004), and CXCL9 (P < 0.008) and CXCL10 (P < 0.003) levels were significantly lower in alloimmunized pregnant women. No significant difference in CCL5 levels was detected between the groups. Fetal RHD genotyping was performed in the alloimmunized RhD⁻ group by real-time PCR. Anti-D alloantibody was detected in 10 mothers and anti-D and -C in six mothers. Twelve fetuses were RHD positive and four were RHD negative. Further studies of serum chemokines and placenta tissue could provide a better understanding of the cells involved in the pathogenesis of maternal erythrocyte alloimmunization.

Fetal RHD Genotyping Using Real-Time Polymerase Chain Reaction Analysis of Cell-Free Fetal DNA in Pregnancy of RhD Negative Women in South of Iran

BACKGROUND

Maternal-fetal RhD antigen incompatibility causes approximately 50% of clinically significant alloimmunization cases. The routine use of prophylactic anti-D immunoglobulin has dramatically reduced hemolytic disease of the fetus and newborn. Recently, fetal RHD genotyping in RhD negative pregnant women has been suggested for appropriate use of anti-D immunoglobulin antenatal prophylaxis and decrease unnecessary prenatal interventions.

MATERIALS AND METHODS

In this prospective cohort study, in order to develop a reliable and non-invasive method for fetal RHD genotyping, cell free fetal DNA (cffD- NA) was extracted from maternal plasma. Real-time quantitative polymerase chain reaction (qPCR) for detection of RHD exons 7, 5, 10 and intron 4 was performed and the results were compared to the serological results of cord blood cells as the gold standard method. SRY gene and hypermethylated Ras-association domain family member 1 (RASSF1A) gene were used to confirm the presence of fetal DNA in male and female fetuses, respectively.

RESULTS

Out of 48 fetuses between 8 and 32 weeks (wks) of gestational age (GA), we correctly diagnosed 45 cases (93.75%) of RHD positive fetuses and 2 cases (4.16%) of the RHD negative one. Exon 7 was amplified in one sample, while three other RHD gene sequences were not detected; the sample was classified as inconclusive, and the RhD serology result after birth showed that the fetus was RhD-negative.

CONCLUSION

Our results showed high accuracy of the qPCR method using cffDNA for fetal RHD genotyping and implicate on the efficiency of this technique to predict the competence of anti-D immunoglobulin administration.

Survey on the prevention and incidence of haemolytic disease of the newborn in Italy

BACKGROUND

In 2010, the Italian Society of Immunohaematology and Transfusion Medicine (SIMTI) carried out a survey of the incidence of haemolytic disease of the newborn (HDN) and the prevention of HDN caused by anti-Rh(D) in Italian Transfusion Structures (TS).

MATERIALS AND METHODS

A questionnaire divided into the following five sections was administered: (i) types of services provided and maintenance of legally required registers, (ii) immunoprophylaxis (IP), (iii) red cell typing and searches for irregular antibodies, (iv) evaluation of foetal-maternal haemorrhage (FMH), and (v) incidence of HDN in 2010. Of the 280 TS sent the questionnaire, 176 (63%) replied.

RESULTS

A HDN register was available in 55.5% of the TS (n =91). Immunoprophylaxis with a dose of anti-D IgG was given to all Rh(D) negative and Rh(D) variant puerpera with Rh(D) positive newborns: in more than 93% of cases the dose was between 1,500 IU (300 μg) and 1,250 IU (250 μg). Antenatal IP between the 25(th) and 28(th) week was proposed by 42 TS (26%). Seventy percent of the TS (n =115) did not make any evaluation of FMH. The number of births surveyed in 2010 was 203,384, the number of Rh(D) negative pregnancies was 13,569, while anti-D antibodies were present in 245 pregnancies. There were 111 cases of HDN due to anti Rh(D) incompatibility and in 40 of these, intrauterine transfusion (n =8) or exchange transfusion (n =32) was necessary. In 94 cases HDN was due to other irregular antibodies: in 4 of these cases intrauterine transfusion was needed and in 11 other recourse was made of exchange transfusion. Finally, there were 1,456 newborns with ABO HDN of whom 13 underwent exchange transfusion.

DISCUSSION

The data collected give a picture of the incidence of HDN in Italy and of the methods of managing IP and could form the basis for an update of the SIMTI recommendations on the management and prevention of this disease.

Cell-free fetal nucleic acid testing: a review of the technology and its applications

Cell-free fetal nucleic acids circulating in the blood of pregnant women afford the opportunity for early, noninvasive prenatal genetic testing. The predominance of admixed maternal genetic material in circulation demands innovative means for identification and analysis of cell-free fetal DNA and RNA. Techniques using polymerase chain reaction, mass spectrometry, and sequencing have been developed for the purposes of detecting fetal-specific sequences, such as paternally inherited or de novo mutations, or determining allelic balance or chromosome dosage. Clinical applications of these methods include fetal sex determination and blood group typing, which are currently available commercially although not offered routinely in the United States. Other uses of cell-free fetal DNA and RNA being explored are the detection of single-gene disorders, chromosomal abnormalities, and inheritance of parental polymorphisms across the whole fetal genome. The concentration of cell-free fetal DNA may also provide predictive capabilities for pregnancy-associated complications. The roles that cell-free fetal nucleic acid testing assume in the existing framework of prenatal screening and invasive diagnostic testing will depend on factors such as costs, clinical validity and utility, and perceived benefit-risk ratios for different applications. As cell-free fetal DNA and RNA testing continues to be developed and translated, significant ethical, legal, and social questions will arise that will need to be addressed by those with a stake in the use of this technology.

TARGET AUDIENCE

Obstetricians & Gynecologists and Family Physicians Learning Objectives: After participating in this activity, physicians should be better able to evaluate techniques and tools for analyzing cell-free fetal nucleic acids, assess clinical applications of prenatal testing, using cell-free fetal nucleic acids and barriers to implementation, and distinguish between relevant clinical features of cell-free fetal nucleic acid testing and existing prenatal genetic screening and diagnostic procedures.

Determination of foetal sex in pregnancies at risk of haemophilia: a qualitative study exploring the clinical practices and attitudes of health professionals in the United Kingdom

In pregnancies at risk of haemophilia, foetal sex determination is used to plan perinatal management and to guide the offer of invasive testing in pregnancies with a male foetus. Traditionally ultrasound from 12 weeks gestation has been used, but recently options for early foetal sex determination have increased following the introduction of non-invasive prenatal diagnosis (NIPD) using cell free foetal DNA in maternal plasma. This study was conducted to identify clinical practices and examine health professional attitudes regarding NIPD for foetal sex determination. A qualitative approach using one-to-one semi structured interviews was used to enable an in-depth exploration of current practice, introduction and use of NIPD and benefits and disadvantages of offering NIPD. Interviews were conducted with consultant haematologists (N = 7), specialist haemophilia nurses (N = 7), genetic counsellors (N = 6), consultants in clinical genetics (N = 5), specialist midwives (N = 2) and obstetricians (N = 5) from 24 services across the United Kingdom (UK). Key differences in how NIPD for foetal sexing is utilized throughout the UK were identified. Some services routinely offered NIPD to all carriers of haemophilia or to all carriers of severe haemophilia, others discussed the value of NIPD with all or primarily offered NIPD as a first step to invasive testing. This study informs our understanding of how NIPD is being utilized and provides unique insights into current practice. The identification of variation between services in how prenatal testing options are offered has implications for future policy and guidelines for prenatal care.

Fetal RHD genotyping by analysis of maternal plasma in a mixed population

BACKGROUND

Maternal plasma analysis for the determination of the fetal RHD status is an exciting tool for the management of RhD-negative pregnant women, specially sensitized women. We assessed the accuracy of fetal RHD genotyping by analysis of maternal plasma in a multi-ethnic population.

METHODS

We analyzed plasma samples from 88 RhD-negative pregnant women between 11 and 39 weeks of gestation, median age of 28 years old to determine the fetal RHD genotype. This population was from Southeastern Brazil with high mixed ethnic background. Fourteen patients (16%) had anti-D alloantibody. We used Taqman primers and probes to detect by real-time PCR, exons 4, 5, and 10 of RHD. As internal controls we used primers/probes sets to SRY and CCR5. Peripheral or umbilical cord bloods from respective neonates were collected during delivery and hemagglutination was performed.

RESULTS

Fifty-eight samples (66%) were genotyped as RHD+, 27 samples (31%) showed complete absence of RHD and 3 samples (3 %) presented a D variant (RHDψ). All the results agreed with the neonatal typing, including the three fetuses with the RHDψ, phenotyped as RhD-negative. Thus, the accuracy of the fetal RHD genotyping in this mixed population was 100%. The earliest pregnancy in which fetal RHD was detected was 11 weeks.

CONCLUSION

Our findings indicate that the accuracy of RHD gene using three regions (exons 4, 5, and 10) can be sufficient for clinical application in a multi-ethnic population. This knowledge helped us on the development of a feasible protocol for fetal RHD genotyping on DNA from maternal plasma for our population.

Restriction enzyme-mediated enhanced detection of circulating cell-free fetal DNA in maternal plasma

A universal method confirming the presence of circulating cell-free fetal (ccff) DNA in maternal plasma is important in the field of noninvasive prenatal diagnostics. Restriction endonuclease digestion of one allele of a single-nucleotide polymorphism (SNP) was used to allow detection of paternal alleles in maternal plasma DNA. Multiplexed genotyping of 92 panethnic high-frequency SNPs predicted >0.99 probability of detecting at least four informative loci per sample. Child-maternal paired DNA samples were used to confirm detection of 2% child's heterozygous DNA in a background of maternal DNA homozygous for the digestible allele. By restriction endonuclease digestion of DNA in a PCR cocktail before thermal cycling, 10 genomic copies of a paternal SNP allele were detectable in a background of 990 maternal SNP alleles. A comparison of 154 pregnant and nonpregnant female plasma DNA samples demonstrated enhanced detection of nondigestible SNP alleles in maternal plasma. Receiver operating characteristic curve analysis showed an optimal detection threshold of four nondigestible SNP alleles in plasma for the confirmation of ccff DNA and 98% sensitivity and 96% specificity at a 95% confidence level. Our study demonstrates the ability of this technique to confirm the presence of paternal alleles from ccff DNA in maternal plasma.

The Bloodgen Project of the European Union, 2003-2009

The Bloodgen project was funded by the European Commission between 2003 and 2006, and involved academic blood centres, universities, and Progenika Biopharma S.A., a commercial supplier of genotyping platforms that incorporate glass arrays. The project has led to the development of a commercially available product, BLOODchip, that can be used to comprehensively genotype an individual for all clinically significant blood groups. The intention of making this system available is that blood services and perhaps even hospital blood banks would be able to obtain extended information concerning the blood group of routine blood donors and vulnerable patient groups. This may be of significant use in the current management of multi-transfused patients who become alloimmunised due to incomplete matching of blood groups. In the future it can be envisaged that better matching of donor-patient blood could be achieved by comprehensive genotyping of every blood donor, especially regular ones. This situation could even be extended to genotyping every individual at birth, which may prove to have significant long-term health economic benefits as it may be coupled with detection of inborn errors of metabolism.