Diagnostic performance of the noninvasive prenatal FetoGnost RhD assay for the prediction of the fetal RhD blood group status

Artificial intelligence and machine learning in cell-free-DNA-based diagnostics

The discovery of circulating fetal and tumor cell-free DNA (cfDNA) molecules in plasma has opened up tremendous opportunities in noninvasive diagnostics such as the detection of fetal chromosomal aneuploidies and cancers and in posttransplantation monitoring. The advent of high-throughput sequencing technologies makes it possible to scrutinize the characteristics of cfDNA molecules, opening up the fields of cfDNA genetics, epigenetics, transcriptomics, and fragmentomics, providing a plethora of biomarkers. Machine learning (ML) and/or artificial intelligence (AI) technologies that are known for their ability to integrate high-dimensional features have recently been applied to the field of liquid biopsy. In this review, we highlight various AI and ML approaches in cfDNA-based diagnostics. We first introduce the biology of cell-free DNA and basic concepts of ML and AI technologies. We then discuss selected examples of ML- or AI-based applications in noninvasive prenatal testing and cancer liquid biopsy. These applications include the deduction of fetal DNA fraction, plasma DNA tissue mapping, and cancer detection and localization. Finally, we offer perspectives on the future direction of using ML and AI technologies to leverage cfDNA fragmentation patterns in terms of methylomic and transcriptional investigations.

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.

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.

Terminating Routine Cord Blood RhD Typing of the Newborns to Guide Postnatal Anti-D Immunoglobulin Prophylaxis Based on the Results of Fetal RHD Genotyping

INTRODUCTION

Targeted routine antenatal prophylaxis with anti-D immunoglobulin (Ig) only to RhD-negative pregnant women who carry RhD-positive fetuses (determined by fetal RHD genotyping) has reduced D-alloimmunization significantly when administered in addition to postnatal prophylaxis. Achieving high analysis sensitivity and few false-negative fetal RHD results will make RhD typing of the newborn redundant. Postnatal prophylaxis can then be given based on the result of fetal RHD genotyping. Terminating routine RhD typing of the newborns in cord blood will streamline maternity care. Accordingly, we compared the results of fetal RHD genotyping with RhD typing of the newborns.

METHODS

Fetal RHD genotyping was performed, and antenatal anti-D Ig was administered at gestational week 24 and 28, respectively. Data for 2017-2020 are reported.

RESULTS

Ten laboratories reported 18,536 fetal RHD genotypings, and 16,378 RhD typing results of newborns. We found 46 false-positive (0.28%) and seven false-negative (0.04%) results. Sensitivity of the assays was 99.93%, while specificity was 99.24%.

CONCLUSION

Few false-negative results support the good analysis quality of fetal RHD genotyping. Routine cord blood RhD typing will therefore be discontinued nationwide and postnatal anti-D Ig will now be given based on the result of fetal RHD genotyping.

Non-invasive prenatal diagnosis (NIPD): current and emerging technologies

Prenatal testing is important for the early detection and diagnosis of rare genetic conditions with life-changing implications for the patient and their family. Gaining access to the fetal genotype can be achieved using gold-standard invasive sampling methods, such as amniocentesis and chorionic villus sampling, but these carry a small risk of miscarriage. Non-invasive prenatal diagnosis (NIPD) for select rare monogenic conditions has been in clinical service in England since 2012 and has revolutionised the field of prenatal diagnostics by reducing the number of women undergoing invasive sampling procedures. Fetal-derived genomic material is present in a highly fragmented form amongst the maternal cell-free DNA (cfDNA) in circulation, with sequence coverage across the entire fetal genome. Cell-free fetal DNA (cffDNA) is the foundation for NIPD, and several technologies have been clinically implemented for the detection of paternally inherited and de novo pathogenic variants. Conversely, a low abundance of cffDNA within a high background of maternal cfDNA makes assigning maternally inherited variants to the fetal fraction a significantly more challenging task. Research is ongoing to expand available tests for maternal inheritance to include a broader range of monogenic conditions, as well as to uncover novel diagnostic avenues. This review covers the scope of technologies currently clinically available for NIPD of monogenic conditions and those still in the research pipeline towards implementation in the future.

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.