Fetal RHD Screening in RH1 Negative Pregnant Women: Experience in Switzerland.

RH1 incompatibility between mother and fetus can cause hemolytic disease of the fetus and newborn. In Switzerland, fetal RHD genotyping from maternal blood has been recommended from gestational age 18 onwards since the year 2020. This facilitates tailored administration of RH immunoglobulin (RHIG) only to RH1 negative women carrying a RH1 positive fetus. Data from 30 months of noninvasive fetal RHD screening is presented. Cell-free DNA was extracted from 7192 plasma samples using a commercial kit, followed by an in-house qPCR to detect RHD exons 5 and 7, in addition to an amplification control. Valid results were obtained from 7072 samples, with 4515 (64%) fetuses typed RHD positive and 2556 (36%) fetuses being RHD negative. A total of 120 samples led to inconclusive results due to the presence of maternal or fetal RHD variants (46%), followed by women being serologically RH1 positive (37%), and technical issues (17%). One sample was typed false positive, possibly due to contamination. No false negative results were observed. We show that unnecessary administration of RHIG can be avoided for more than one third of RH1 negative pregnant women in Switzerland. This reduces the risks of exposure to a blood-derived product and conserves this limited resource to women in actual need

Noninvasive fetal RHD genotyping to guide targeted anti-D prophylaxis-an external quality assessment workshop.

Background and Objectives: FetalRHDgenotyping of cell-free fetal DNA fromRhD-negative pregnant women can be used to guide targeted antenatal and post-natal anti-D prophylaxis for the prevention of RhD immunization. To assure thequality of clinical testing, we conducted an external quality assessment workshopwith the participation of 28 laboratories. Materials and Methods: Aliquots of pooled maternal plasma were sent to eachlaboratory. One sample was positive, and the second sample was negative forfetalRHD, verified by pre-workshop testing using quantitative real-time PCR(qPCR) analysis ofRHDexons 4, 5, 7 and 10. Plasma samples were shipped atroom temperature. A reporting scheme was supplied for data collection, includingquestions regarding the methodological setup, results and clinical recommenda-tions. Different methodological approaches were used, all employing qPCR with atotal of eight different combinations ofRHDexon targets. The samples weretested blindly. Results: FetalRHDgenotyping was performed with no false-negative and nofalse-positive results. One inconclusive result was reported for theRHD-positivesample, and four inconclusive results were reported for theRHD-negative sample.All clinical conclusions were satisfactory. Conclusion: This external quality assessment workshop demonstrates that despitethe different approaches taken to perform the clinical assays, fetalRHDgenotyp-ing is a reliable laboratory assay to guide targeted use of Rh prophylaxis in aclinical setting

Noninvasive Antenatal Determination of Fetal Blood Group Using Next-Generation Sequencing

Hemolytic disease of the fetus and newborn (HDFN) is a condition characterized by a decreased lifespan of fetal red blood cells caused by maternally produced allospecific antibodies transferred to the fetus during pregnancy. The antibodies bind to the corresponding blood group antigens on fetal red blood cells and induce hemolysis. Cell-free DNA derived from the conceptus circulates in maternal blood. Using next-generation sequencing (NGS), it can be determined if this cell-free fetal DNA encodes the corresponding blood group antigen that is the target of the maternal allospecific antibodies. This determination carries no risk to the fetus. It is important to determine if the fetus is at risk of hemolysis to enable timely intervention. Many tests for blood groups are based solely on the presence or absence of a single nucleotide polymorphism (SNP). Antenatal determination of fetal blood group by NGS analysis holds advantages over polymerase chain reaction (PCR) determination based on allele specific amplification

Genotyping to prevent Rh disease: has the time come?

In this review, we analyzed the current literature on noninvasive fetal RHD typing to answer the question whether the administration of RhIg to prevent D-alloimmunization during pregnancy can be safely guided by fetal RHD typing. Recently the first centers that implemented large-scale nationwide fetal RHD typing in the second trimester for targeted RhIg administration have published their studies evaluating the diagnostic accuracy of their screening programs. These data show that fetal RHD typing in a routine setting is, at least in a population of European descent, accurate enough to guide both antenatal and postnatal immunoprophylaxis. Depending on the ethnic background and the organization of pregnancy care the decisions regarding RhIg can be safely and cost-effectively based on fetal RHD typing by a duplex real-time PCR. As a result, the unnecessary administration of 40% of antenatal RhIg can be prevented, and cord blood serology can be omitte