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Objectives: To assess the accuracy of fetal RHD genotyping using cell-free fetal DNA in maternal plasma at different gestational ages., Design: A prospective multicentre cohort study., Setting: Seven maternity units in England., Participants: RhD negative pregnant women who booked for antenatal care before 24 weeks' gestation., Interventions: Women who gave consent for fetal RHD genotyping had blood taken at the time of booking for antenatal care and, when possible, at other routine visits such as for Down's syndrome screening between 11 and 21 weeks' gestation, at the anomaly scan at 18-21 weeks, and in the third trimester when blood was taken for the routine antibody check. The results of cord blood analysis, done routinely in RhD negative pregnancies, were also obtained to confirm the fetal RHD genotyping., Main Outcome Measures: The accuracy of fetal RHD genotyping compared with RhD status predicted by cord blood serology., Results: Up to four analyses per woman were performed in 2288 women, generating 4913 assessable fetal results. Sensitivity for detection of fetal RHD positivity was 96.85% (94.95% to 98.05%), 99.83% (99.06% to 99.97%), 99.67% (98.17% to 99.94%), 99.82% (98.96% to 99.97%), and 100% (99.59% to 100%) at <11, 11-13, 14-17, 18-23, and >23 completed weeks' gestation, respectively. Before 11 weeks' gestation 16/865 (1.85%) babies tested were falsely predicted as RHD negative., Conclusions: Mass throughput fetal RHD genotyping is sufficiently accurate for the prediction of RhD type if it is performed from 11 weeks' gestation. Testing before this time could result in a small but significant number of babies being incorrectly classified as RHD negative. These mothers would not receive anti-RhD immunoglobulin, and there would be a risk of haemolytic disease of the newborn in subsequent pregnancies., (© Chitty et al 2014.)

Objective: To examine the feasibility of fetal RHD genotyping at 11-13 weeks' gestation from analysis of circulating cell-free fetal DNA (ccffDNA) in the plasma of RhD negative pregnant women using a high-throughput robotic technique., Methods: Stored plasma (0.5 ml) from 591 RhD negative women was used for extraction of ccffDNA by a robotic technique. Real-time quantitative polymerase chain reaction (PCR) with probes for exons 5 and 7 of the RHD gene was then used to determine the fetal RHD genotype, which was compared to the neonatal RhD phenotype., Results: In total there were 502 (85.7%) cases with a conclusive result and 84 (14.3%) with an inconclusive result. The prenatal test predicted that the fetus was RhD positive in 332 cases and in all of these the prediction was correct, giving a positive predictive value of 100% (95% CI 96.8-100). The test predicted that the fetus was RhD negative in 170 cases and in 164 of these the prediction was correct, giving a negative predictive value for RhD positive fetuses of 96.5% (95% CI 93.7-99.2)., Conclusion: The findings demonstrate the feasibility and accuracy of non-invasive fetal RHD genotyping at 11-13 weeks with a high-throughput technique., (Copyright © 2011 S. Karger AG, Basel.)

Identification of the molecular basis of the D polymorphism of the Rh blood group system in the 1990s made it possible to predict D phenotype from DNA. The most valuable application of this has been the determination of fetal D type in pregnant D-negative women with anti-D. Knowledge of fetal D type reveals whether the fetus is at risk of hemolytic disease of the fetus and newborn so that the pregnancy can be managed appropriately. Noninvasive fetal D typing for D-negative pregnant women with anti-D, performed on the small quantity of fetal DNA present in the blood of pregnant women, is now routine practice in several European countries. Noninvasive fetal blood grouping for C, c, E, and K also may be provided as a routine service for alloimmunized pregnant women. In many countries, all D-negative pregnant women are offered anti-D prophylaxis antenatally, yet in a predominantly Caucasian population, about 38% will be carrying a D-negative fetus and will receive the treatment unnecessarily. Large-scale trials to ascertain the accuracy of high-throughput, automated methods suggest that fetal D screening of all D-negative pregnant women is feasible, and it is likely that fetal D screening in D-negative pregnant women will be policy in some European countries within the next few years., (Copyright (c) 2010 Elsevier Inc. All rights reserved.)

Background: Alloimmunization against the fetal Kell (KEL1) blood group antigen is gaining importance relative to the Rhesus problem and is the second most important cause of hemolytic disease of the fetus and newborn. Molecular diagnosis for fetal KEL1, which currently involves invasive procedures, is routinely done for accessing whether a fetus is at risk. Here we developed a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)-based single allele-based extension reaction (SABER) to examine the fetal KEL1 gene from KEL1-negative pregnant women using cell-free fetal DNA in maternal plasma., Methods: Thirty-two maternal plasma samples taken at the second and third trimesters of gestation (median: 21.5 weeks) were examined with MALDI-TOF MS-based SABER. The results were confirmed by serological tests on cord blood or polymerase chain reaction (PCR) typing on amniocyte-derived fetal DNA., Results: We were able to detect the fetal KEL1 allele in 11 of the 13 KEL1-positive samples. No false positive results were scored. The paternal KEL1 allele could be correctly determined in 94% of cases (30/32)., Conclusions: Our results indicated that the MALDI-TOF MS-based SABER has been used successfully for the detection of the fetal KEL1 status with the accuracy of 94%. Further, large-scale study, such as multicenter study, can now be explored for clinical application., (Copyright (c) 2008 John Wiley & Sons, Ltd.)

The most important application of blood group genotyping by molecular genetics is the prediction of fetal RhD phenotype in pregnant women with anti-D, in order to assess the risk of haemolytic disease of the fetus and newborn. This diagnostic test performed on cell-free fetal DNA in the maternal plasma, is now a routine procedure in some countries. High-throughput modifications of this form of fetal D-typing would be valuable for testing fetuses of all D-negative pregnant women to avoid unnecessary antenatal treatment with anti-D immunoglobulin in the 40% of D-negative pregnant women with a D-negative fetus. The results of trials in Bristol and Amsterdam suggest that such routine testing is feasible and accurate.

Prediction of fetal blood group from DNA is usually performed when the mother has antibodies to RhD, to assess whether the fetus is at risk from hemolytic disease of the fetus and newborn (HDFN). Over the last five years RhD testing on fetal DNA in maternal plasma has been introduced. At the International Blood Group Reference Laboratory (IBGRL) we employ real-time quantitative polymerase chain reaction (RQ-PCR) to detect RHD exons 4, 5, and 10, which also reveals RHDpsi. SRY and, in RhD-negative (RhD-) females, eight biallelic polymorphisms are incorporated in an attempt to provide an internal positive control. Since 2000 we have tested 533 pregnancies for RhD. In 327 pregnancies where the RhD of the infant is known, we had one false-positive and one false-negative result. In 2004 we introduced fetal typing from DNA in maternal plasma for K, Rhc, and RhE, which represent single nucleotide polymorphisms (SNPs) on the KEL and RHCE genes. We have begun trials on an automated method for fetal RhD typing from DNA in maternal plasma. This is designed to test fetal RhD in all pregnant RhD- women, to identify the 40% with an RhD- fetus so that antenatal RhD immunoglobulin (Ig) prophylaxis can be avoided. Similar trials have already been reported by Sanquin Research Laboratories in Amsterdam.

The cloning of blood group genes and subsequent identification of the molecular bases of blood group polymorphisms has made it possible to predict blood group phenotypes from DNA with a reasonable degree of accuracy. The major application of this technology, which has now become the standard of care, is the determination of a fetal RHD genotype in women with anti-D, to assess whether the fetus is at risk of haemolytic disease of the fetus and newborn (HDFN). Initially, the procurement of fetal DNA required the invasive procedures of amniocentesis or chorionic villus sampling. Since the discovery of fetal DNA in maternal plasma in 1997, the technology of detecting an RHD gene in this very small quantity of fetal DNA has developed rapidly, so that non-invasive fetal D typing can now be provided as a diagnostic service for D-negative pregnant women with anti-D. Within a few years, it is probable that fetuses of all D-negative pregnant women will be tested for RHD, to establish whether the mother requires antenatal anti-D immunoglobulin prophylaxis.

Antenatal determination of fetal blood group is important in pregnancies with a significant risk of hemolytic anemia due to maternal alloimmunization. The International Blood Group Reference Laboratory (part of the National Blood Service) in Bristol, UK, provides a fetal blood group genotyping service to obstetricians caring for immunized pregnant women with heterozygous partners. Since 2001, fetal D typing has been offered using free fetal DNA in maternal plasma. Real-time polymerase chain reaction (PCR) assays are performed to detect the RHD gene. To confirm the presence of fetal DNA when RHD is not detected, Y-chromosome sequences are targeted. When a D-negative female fetus is predicted, maternal buffy coat DNA is tested for eight insertion/deletion polymorphisms. Sequences that are absent from the maternal genome are then targeted in maternal plasma and are used to confirm the presence of free fetal DNA in the blood sample. Currently, 283 pregnancies have been tested, of which 50 are awaiting confirmatory results. Fetal D status was correctly predicted in 223 cases, and no result was obtainable in 7 cases. In three cases, serology on cord blood was discrepant with reported results, but all fetuses had received multiple intrauterine transfusions. The new test has significantly reduced the number of invasive procedures carried out in the UK for fetal D grouping. Antenatal anti-D prophylaxis is currently being introduced in the UK to all D-negative women; in the future, detection of fetal RHD sequences in maternal plasma may allow anti-D to be restricted to pregnancies involving a D-positive fetus.

Background: Invasive procedures to obtain fetal DNA for prenatal blood grouping present a risk to the fetus. During pregnancy, cell-free fetal DNA is present in maternal blood. The detection of RHD sequences in maternal plasma has been used to predict fetal D status, based on the assumption that RHD is absent in D- genomes., Study Design and Methods: Real-time PCR assays were designed to distinguish RHD from RHDpsi (possessed by the majority of D- black Africans). Plasma-derived DNA from 137 D- women was subjected to real-time PCR to detect fetal RHD and Y chromosome-associated SRY sequences. The accuracy of RHD genotyping from maternal plasma was investigated by comparing results with those obtained by conventional RHD genotyping from fetal tissue or serologic tests on the infant's RBCs. The quantity of fetal DNA in maternal plasma was investigated in 94 pregnancies., Results: Fetal D status was predicted with 100-percent accuracy from maternal plasma. The number of copies of fetal DNA in maternal plasma was found to increase with gestation., Conclusion: Combination of the sensitivity of real-time PCR with an improved RHD typing assay to distinguish RHD from RHDpsi enables highly accurate prediction of fetal D status from maternal plasma. This has resulted in the implementation of a clinical noninvasive fetal RHD genotyping service.

Background and Objectives: The prenatal determination of fetal blood group status by molecular techniques has been used in the clinical management of alloimmunised pregnancies for seven years, in particular for the definition of fetal Rh D, c and E, K, Fya and Jka status. This has arisen in response to the definition of the molecular bases of human blood group polymorphism., Materials and Methods: PCR-based amplification assays have been designed to define fetal blood group status, where the source of template DNA is normally derived from amniotic fluid or chorionic villus. Recently, non-invasive methods have been explored to obtain fetal DNA from maternal peripheral blood., Results: PCR-based tests are now available to screen for all fetal medicine significant blood group antigens. The Rh system is the most complex, and assays to define Rh genotype have been modified in response to our increased understanding of the molecular biology of this blood group system., Conclusion: Prenatal diagnosis of fetal blood group status is now in widespread use in the clinical management of HDN. Non-invasive testing, if applied in the clinical setting may invoke a dramatic increase in the numbers of pregnancies that may be analysed prenatally.