Laboratory assays for predicting the severity of haemolytic disease of the fetus and newborn

Immunohematological testing and transfusion management of the prenatal patient

The primary indication for immunohematological testing in the prenatal patient is to detect and identify maternal red cell antibodies. If there are antibodies that are expected to hemolyze the fetus' red cells, their strength of reactivity must be tested, and the fetus' antigen status determined. After delivery, testing is performed to assess the extent of fetomaternal hemorrhage, as a large hemorrhage may require other therapeutic interventions. Another major role for immunohematological testing is to select blood components appropriately when intrauterine transfusion is required for fetal anemia resulting from maternal alloimmunization or some other cause. Supplementation with molecular methods has transformed the practice of immunohematology, particularly as it applies to typing for the D antigen of the Rh blood group system. Notwithstanding the advances in testing, close coordination and communication between the transfusion service and the obstetrics service are the foundation for ensuring the finest care for prenatal patients, and for new mothers and their infants. This review describes testing and transfusion practices for prenatal patients, using case presentations to highlight the management of selected immunohematological findings. It also includes a discussion of key patient management topics that are currently unresolved.

Identification and management of fetal anemia due to hemolytic disease

INTRODUCTION

Hemolytic disease of the fetus and newborn (HDFN) is a condition caused by maternal alloantibodies against fetal red blood cells (RBCs) that can cause severe morbidity and mortality in the fetus and newborn. Adequate screening programs allow for timely prevention and intervention resulting in significant reduction of the disease over the last decades. Nevertheless, HDFN still occurs and with current treatment having reached an optimum, focus shifts toward noninvasive therapy options.

AREAS COVERED

This review focusses on the timely identification of high risk cases and antenatal management. Furthermore, we elaborate on future perspectives including improvement of screening, identification of high risk cases and promising treatment options.

EXPERT OPINION

In high-income countries mortality and morbidity rates due to HDFN have drastically been reduced over the last decades, yet worldwide anti-D mediated HDFN still accounts for 160,000 perinatal deaths and 100,000 patients with disabilities every year. Much of these deaths and disabilities could have been avoided with proper identification and prophylaxis. By implementing sustainable prevention, screening, and disease treatment measures in all countries this will systemically reduce unnecessary perinatal deaths. There is a common responsibility to engage in this cause.

Neonatal outcomes following intrauterine transfusion for hemolytic disease of the fetus and newborn: a twenty-year service review

OBJECTIVE

The primary objective was to explore perinatal and neonatal outcomes amongst infants who received intrauterine transfusion (IUT) for the management of hemolytic disease of the fetus and newborn (HDFN). The secondary objective was to evaluate the role of key investigations in the fetus at risk of HDFN and assess the relationship with neonatal outcomes. We hypothesized that middle cerebral artery peak systolic velocity (MCA-PSV) and corresponding multiples of the median (MoM) would be predictive of neonatal course.

METHODS

This was a retrospective observational study conducted at a tertiary center in the United Kingdom between January 2000 and August 2020. Trust approval was obtained to conduct this service review. Pregnancies requiring IUT for HDFN were identified using the fetal medicine department database. Inclusion criteria were infants who received IUT for HDFN. 67 pregnancies were eligible for inclusion in the study with 156 IUT events. Data were extracted using healthcare records. Statistical analysis was performed using SPSS version 28.0, data were assessed for normality and Spearman's correlation analysis was performed with p values < .05 considered significant.

RESULTS

67 pregnancies were included in the study which led to the live birth of 68 infants (one twin pregnancy). There were no fetal deaths following IUT. There was one neonatal death due to extreme prematurity following spontaneous vaginal delivery at 23 + 4 weeks gestation, occurring three days following IUT. 97% of infants required admission to the neonatal intensive care unit and 88% required phototherapy. 25% of infants required readmission for red blood cell transfusion due to anemia. There was a significant correlation between maternal anti-D antibody levels and length of neonatal admission r = 0.477, p = .014. MCA-PSV and MoM measured prior to the last IUT had a significant positive correlation with the duration of phototherapy: r = 0.527 (p < .001) and r = 0.313 (p < .05) respectively. Linear regression analysis demonstrated a significant positive relationship between MCA-PSV and corresponding MoM recorded prior to the last IUT with r²= 0.177 (p = .003) and r²= 0.101 (p = .029).

CONCLUSION

HDFN is an important cause of fetal anemia associated with significant neonatal morbidity. MCA-PSV and MoM may be predictive of neonatal phototherapy requirements. The predictive value of MCA-PSV appears to be dependent on the timing of measurement during the antenatal period and more research is needed. Multicentre collaboration is required to generate a reliable large-scale database to further delineate the value of MCA-PSV and MoM and predict neonatal outcomes in cases of HDFN requiring IUT. This data would assist clinicians in antenatal planning and enable more informed counseling of parents in the antenatal period.

Afucosylated IgG responses in humans - structural clues to the regulation of humoral immunity

Healthy immune responses require efficient protection without excessive inflammation. Recent discoveries on the degree of fucosylation of a human N-linked glycan at a conserved site in the immunoglobulin IgG-Fc domain might add an additional regulatory layer to adaptive humoral immunity. Specifically, afucosylation of IgG-Fc enhances the interaction of IgG with FcγRIII and thereby its activity. Although plasma IgG is generally fucosylated, afucosylated IgG is raised in responses to enveloped viruses and Plasmodium falciparum proteins expressed on infected erythrocytes, as well as during alloimmune responses. Moreover, while afucosylation can exacerbate some infectious diseases (e.g., COVID-19), it also correlates with traits of protective immunity against malaria and HIV-1. Herein we discuss the implications of IgG afucosylation for health and disease, as well as for vaccination.

Implementation of a Standardized Prenatal Testing Protocol in an Integrated, Multihospital Health System

OBJECTIVES

When our institution grew into an integrated multihospital health system, we were faced with the need to standardize laboratory processes, including blood bank processes, across all locations. The purpose of this article is to describe our experience of standardizing the protocols for prenatal testing.

METHODS

For each hospital in the system, we established service tiers to define tests offered on site or referred to another location. For each prenatal test, we examined the related processes for ways to improve uniformity, efficiency, and reliability. Throughout this process of standardization, we collaborated with the clinical services to gain concurrence on the interpretation and reporting of results.

RESULTS

We created and implemented a uniform protocol for testing prenatal patients. The protocol standardized the definition of critical titer, instituted criteria to identify passively acquired anti-D, and established a process for the follow-up of women with inconsistent serologic results on Rh(D) typing.

CONCLUSIONS

Close collaboration with the clinical services ensured that our testing protocol is aligned with the needs of the integrated obstetrics service in the health system. The approach described in this article may provide a plan outline for pathologists facing similar challenges at other integrated health systems.

An Unusual Case of Hemolytic Disease of Newborn Due to ABO and Rh Isoimmunization

Anti-D is the most common cause of hemolytic disease of the newborn (HDN) in the developing countries even after the introduction of anti-D immunoprophylaxis. Still, ABO incompatibility and other alloantibodies against minor blood group antigens have emerged as significant causes of HDN. Moreover, ABO incompatibility acts as a protective barrier to the expression of Rh isoimmunization. Here we are presenting a case of HDN where both Rh and ABO incompatibility co-existed with their manifestations in a B positive neonate born to an O positive mother. Use of appropriate elution technique can aid in the diagnosis of such cases. Hence, antenatal screening of all mothers irrespective of their Rh D status can help in early diagnosis and proper management that can decrease the neonatal morbidity and mortality.

Silent red blood cell autoantibodies: Are they naturally occurring or an effect of tolerance loss for a subsequent autoimmune process?

Unexpected anti-red blood cell (RBC) alloantibodies are routinely investigated in immunohematology and blood banking since their existence in pregnant women may induce haemolytic disease of the foetus and newborn, and their presence in donors may induce haemolytic transfusion reactions or hyperacute rejection in solid organ transplantation. Unexpected anti-RBC alloantibodies may target antigens of the most blood types excluding the expected antibodies targeting the ABO antigens. Their incidence in humans was originally linked to alloimmunization events such as blood transfusions, transplants, or pregnancies. But later, many findings revealed their existence in pathogenic processes such as malignancies, infections, and autoimmune diseases; and usually (but not always) associated to autoimmune haemolytic anaemia (AIHA). Nevertheless, unexpected anti-RBC autoantibodies are also occasionally found in healthy individuals in the absence of AIHA and with no history of alloimmunization or the associated pathologic processes. Hence, they are generally known as non-clinically significant, are excluded for typification and called "silent red blood cell autoantibodies (SRBCAA)". This review highlights evidence related to genetic predisposition, molecular mimicry, immune dysregulation, and immune tolerance loss surrounding the existence of anti-RBC antibodies, describing the presence of SRBCAA as possible early witnesses of the development of autoimmune diseases.

Monitoring of prenatal patients using a combined antibody titre for Rh and non-Rh antibodies

OBJECTIVES

This was a laboratory exercise designed to determine whether combined antibody titrations in the presence of multiple antibodies achieve a critical level earlier or at the same time as antibodies having individual antibody titrations.

BACKGROUND

Management of haemolytic disease of the fetus and newborn involves monitoring maternal antibody concentration by antibody titration. Separate titrations are generally performed for each antibody.

METHOD

Thirty-one samples containing combinations of two different Rh and/or non-Rh antibodies were examined with separate titres for each antibody and one single combined titration.

RESULTS

Of 31 samples, 19 (61.3%) showed an increased combined titre. Of 12 samples that showed no increase, 10 contained a separate titre of <1 for either one or both antibodies. Where both antibodies had a separate titre of ≥1, 15 of 17 (88.2%) showed an increased combined titre. In contrast to the separate titration method, no decrease in titre level was observed using the combined method.

CONCLUSION

Where two antibodies are present, titrations performed by a combined method will produce titre levels equal to or higher than antibodies titred individually. Therefore, a combined titration can be expected to reach a critical titre level as early as, or earlier in gestation than, antibodies monitored by a single titration method. Further studies relating fetal outcomes to titration methodology would be valuable in determining the validity of this approach for prenatal management. Cost-effectiveness of this approach to prenatal screening should also be assessed.

A case of mild HDFN caused by anti-C, anti-D, and anti-G: Diagnostic strategy and clinical significance of distinguishing anti-G from anti-D and anti-C

Anti-G is commonly present with anti-D and anti-C and can confuse serological investigations. The differentiation of anti-G from anti-D and anti-C is particularly essential for the accurate diagnosis of hemolytic disease of the fetus and newborn (HDFN) and appropriate administration of anti-D immunoglobulin prophylaxis in Rhesus (Rh) negative women. We reported a rare case of anti-G together with anti-D and anti-C in a pregnant woman and her female neonate. The titers of IgG anti-D, anti-C, and anti-G in the woman were 256, 128, and 32, respectively. While the titers of IgG anti-D, anti-C, and anti-G in the neonate were 16, 8, and 4, respectively. The neonate experienced mild HDFN and only received phototherapy during hospitalization. This report discusses the diagnostic strategy and clinical significance of differentiating anti-G from anti-D and anti-C.

Predicting anti-Kell-mediated hemolytic disease of the fetus and newborn: diagnostic accuracy of laboratory management

BACKGROUND

There is controversy on critical cut-off values of laboratory testing to select pregnancies at increased risk for anti-Kell-mediated hemolytic disease of the fetus and newborn. Without early detection and treatment, anti-Kell-mediated hemolytic disease of the fetus and newborn may result in progressive fetal anemia, fetal hydrops, asphyxia, and perinatal death.

OBJECTIVE

We aimed to determine the value of repeated anti-Kell titer determination and biological activity measurement using the antibody-dependent cellular cytotoxicity test determination in the management of pregnancies at risk for anti-Kell-mediated hemolytic disease of the fetus and newborn.

STUDY DESIGN

This was a retrospective cohort study of pregnancies with anti-Kell and a Kell-positive fetus, identified from January 1999 through April 2015. Laboratory test results and clinical outcome were collected from the Dutch nationwide screening program and the national reference center for fetal therapy in The Netherlands, the Leiden University Medical Center. Diagnostic accuracy was measured (receiver operating characteristic curves, sensitivity, specificity, positive and negative predictive values) for anti-Kell titers and antibody-dependent cellular cytotoxicity test. The relationship between the titer and antibody-dependent cellular cytotoxicity measurements and the 2 foregoing measurements were computed with a Pearson product-moment correlation coefficient.

RESULTS

In a 16-year unselected cohort, representing screening results of 3.2 million pregnancies resulting in live births in The Netherlands, we identified 1026 Kell-immunized pregnancies. In all, 93 pregnant women had anti-Kell and a Kell-positive child, without other red cell alloantibodies. In all, 49 children (53%) needed intrauterine or postnatal transfusion therapy. The first anti-Kell titer showed already a high diagnostic accuracy with an area under the curve of 91%. The optimal cut-off point for the titer was 4 (sensitivity 100%; 95% confidence interval, 91-100), specificity 27% (95% confidence interval, 15-43), and positive predictive value 60% (49-71%). The antibody-dependent cellular cytotoxicity test was not informative to select high-risk pregnancies. Linear regression showed no significant change during pregnancy, when antibody titer and antibody-dependent cellular cytotoxicity test results were compared with every 2 foregoing measurements (P < .0001).

CONCLUSION

Early determination of the anti-Kell titer is sufficient to select pregnancies at increased risk for hemolytic disease of the fetus and newborn with need for transfusion therapy. If the Kell status of the fetus is known to be positive, a titer of ≥4 can be used to target intensive clinical monitoring.

Anti-D Antibodies in Pregnant D Variant Antigen Carriers Initially Typed as RhD

BACKGROUND

To evaluate the incidence, the consequences, and the prevention strategy of anti-D alloimmunizations of D variant carriers in the obstetric population of Split-Dalmatia County, Croatia.

METHODS

RhD immunization events were evaluated retrospectively for the period between 1993 and 2012. Women were tested for RhD antigen and irregular antibodies. Those with anti-D antibody who were not serologically D- were genotyped for RHD. They were evaluated for their obstetric and transfusion history and their titer of anti-D. The neonates were evaluated for RhD status, direct antiglobulin test (DAT), hemoglobin and bilirubin levels, transfusion therapy as well as phototherapy and outcome.

RESULTS

Out of 104,884 live births 102,982 women were tested for RhD antigen. Anti-D immunization occurred in 184 women which accounts for 0.9% of individuals at risk of anti-D formation. 181 cases occurred in women serologically typed as D-. Three women were partial D carriers (DVa n = 2, DNB n = 1), initially typed RhD+, and recognized as D variant carriers after the immunization occurred. Anti-D titer varied from 1:1 to 1:16. Six children were RhD+, four had positive DAT, and two underwent phototherapy.

CONCLUSION

Anti-D immunization occurred in pregnant partial D carriers (DVa, DNB). RhD+ children had serologic markers of hemolytic disease of the fetus and newborn (HDFN), with no cases of severe HDFN.

Estimating the Risk of ABO Hemolytic Disease of the Newborn in Lagos

Background. ABO hemolytic disease of the newborn is the most common hemolytic consequence of maternofetal blood group incompatibility restricted mostly to non-group-O babies of group O mothers with immune anti-A or anti-B antibodies. Aim. We estimated the risk of ABO HDN with view to determining need for routine screening for ABO incompatibility between mother and fetus. Materials and Methods. Prevalence of ABO blood group phenotypes in blood donors at the donor clinic of the Lagos University Teaching Hospital and arithmetic methods were used to determine population prevalence of ABO genes. We then estimated proportion of pregnancies of group O mothers carrying a non-group-O baby and the risk that maternofetal ABO incompatibility will cause clinical ABO HDN. Results. Blood from 9138 donors was ABO typed. 54.3%, 23%, 19.4%, and 3.3% were blood groups O, A, B, and AB, respectively. Calculated gene frequencies were 0.1416, 0.1209, and 0.7375 for A, B, and O genes, respectively. It was estimated that 14.3% of deliveries will result in a blood group O woman giving birth to a child who is non-group-O. Approximately 4.3% of deliveries are likely to suffer ABO HDN with 2.7% prone to suffer from moderately severe to severe hemolysis.

Haemolytic disease of the fetus and newborn

Haemolytic Disease of the Fetus and Newborn (HDFN) is caused by maternal alloimmunization against red blood cell antigens. In severe cases, HDFN may lead to fetal anaemia with a risk for fetal death and to severe forms of neonatal hyperbilirubinaemia with a risk for kernicterus. Most severe cases are caused by anti-D, despite the introduction of antental and postnatal anti-D immunoglobulin prophylaxis. In general, red blood cell antibody screening programmes are aimed to detect maternal alloimmunization early in pregnancy to facilitate the identification of high-risk cases to timely start antenatal and postnatal treatment. In this review, an overview of the clinical relevance of red cell alloantibodies in relation to occurrence of HDFN and recent views on prevention, screening and treatment options of HDFN are provided.

Study of 25 cases of exchange transfusion by reconstituted blood in hemolytic disease of newborn

This study was aimed to review and establish the practice of exchange transfusion (ET) with reconstituted blood in neonates and to observe fall of bilirubin and its comparison with related studies. Twenty-five neonates diagnosed as hemolytic disease of newborn (HDN) were selected for this study, in which exchange transfusion was carried out as one of the treatments for hyperbilirubinemia. Out of the 25 cases, 15 were of Rhesus (Rh) HDN, while ABO and other blood groups constituted 6 and 4 HDN cases respectively. First, the neonates's and mother's blood samples were subjected to relevant investigations. After that, for neonates having Rh HDN, O Rh negative cells suspended in AB plasma were given, O Rh positive cells suspended in AB plasma were given to ABO HDN; and O positive cells, which were indirect Coomb's cross-matched compatible with neonates’ and mother's serum / plasma, suspended in AB plasma were given to the neonates having HDN because of other blood group antibodies. The exchange transfusion (ET) was carried out taking all aseptic precautions by Push-Pull technique with double-volume exchange transfusion method. The average post-exchange fall in serum indirect bilirubin was (52.01%) in all 25 cases, which was found to be more significant than the previous studies. Looking into the superiority of the exchange transfusion in HDN by reconstituted blood, the reconstituted blood can be modified and supplied as per the requirement and conditions.

Diagnostic laboratory technologies for the fetus and neonate with isoimmunization

Maternal-fetal blood group incompatibility is common but less commonly results in hemolytic disease of the fetus and newborn (HDFN). HDFN is associated with greater peak bilirubin, at an earlier age, and for longer duration than other causes of hyperbilirubinemia. It poses a substantial risk for kernicterus and accounts for the majority of exchange transfusions for hyperbilirubinemia. Advances in diagnosis and management are described, from identification of the alloimmunized pregnancy by maternal ABO and Rh typing, antibody screen (indirect Coombs test), identification and titration; laboratory evaluation of the maternal-fetal unit with a critical maternal antibody titer to prompt fetal antigen status determination; assessment of fetomaternal hemorrhage by conventional Kleihauer-Betke testing or by flow cytometric methodology; to antenatal management of isoimmunization and fetal status assessments using the systems of Liley, Queenan, and serial Doppler fetal middle cerebral artery peak velocity measurements. The utility of laboratory diagnostics in the approach to hemolysis in the neonate, including hematology, chemistry, and peripheral blood smear review, is reviewed. The goal of management, to deliver a healthy infant at or near term, is attained for the majority of cases using current modalities; future directions include noninvasive genotyping of fetal blood from maternal serum to fully eliminate RhD alloimmunization and HDFN; and development of prophylaxis and intervention strategies for non-RhD alloimmunizations for which immune globulin is currently unavailable.

HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia

BACKGROUND

The antenatal management of fetomaternal alloimmune thrombocytopenia (FMAIT) due to HPA-1a antibodies remains controversial, and a test identifying pregnancies that do not require therapy would be of clinical value.

STUDY DESIGN AND METHODS

The statistical correlation was analyzed between clinical outcome and 1) anti-HPA-1a potency in maternal serum samples determined by a monoclonal antibody immobilization of platelet (PLT) antigen assay with an international anti-HPA-1a potency standard and 2) anti-HPA-1a biological activity measured by a monocyte chemiluminescence (CL) assay.

RESULTS

A total of 133 pregnancies with FMAIT due to anti-HPA-1a were analyzed. In 97 newly diagnosed cases, there was no difference in antibody potency or CL signal between cases with intracranial hemorrhage (ICH; n = 15), those with no ICH but a PLT count of less than 20 x 10(9) per L (n = 52), and those with a PLT count of at least 20 x 10(9) per L (n = 30). In 22 previously known pregnancies, the positive predictive value of maternal anti-HPA-1a of greater than 30 IU per mL for a PLT count of less than 20 x 10(9) per L was 90 percent, but the negative predictive value was only 66 percent. Antibody potency tended to stay stable throughout pregnancy (n = 16) and from one pregnancy to the next (n = 16).

CONCLUSION

Neither severe thrombocytopenia nor ICH in HPA-1a-alloimmunized pregnancies can be predicted with sufficient sensitivity and specificity for clinical application from maternal anti-HPA-1a potency or bioactivity.

Red cell antigens: Structure and function

Landsteiner and his colleagues demonstrated that human beings could be classified into four groups depending on the presence of one (A) or another (B) or both (AB) or none (O) of the antigens on their red cells. The number of the blood group antigens up to 1984 was 410. In the next 20 years, there were 16 systems with 144 antigens and quite a collection of antigens waiting to be assigned to systems, pending the discovery of new information about their relationship to the established systems. The importance of most blood group antigens had been recognized by immunological complications of blood transfusion or pregnancies; their molecular structure and function however remained undefined for many decades. Recent advances in molecular genetics and cellular biochemistry resulted in an abundance of new information in this field of research. In this review, we try to give some examples of advances made in the field of 'structure and function of the red cell surface molecules.'

Transfusion-Related Risks of Intradermal Allogeneic Lymphocyte Immunotherapy: Single Cases in a Large Cohort and Review of the Literature

PROBLEM

Lymphocyte immunotherapy (LIT) is applied in infertility treatment. Moreover, it has been suggested for prevention of rhesus D-hemolytic disease and as a vaccine for reduction of human immunodeficiency virus-1 susceptibility. Although transfusion-related problems have been rarely reported they were a matter of debate. Here we discuss extensive single-center experience with intradermal LIT for implantation failure and recurrent miscarriages.

METHOD OF STUDY

Retrospective 2- to 3-year follow-up of in vitro fertilization couples treated during 1996-2002 (feedback 2,848/3,041 = 93%), registering 930 deliveries. Prospective survey for acute reactions for 2000-2003 (feedback 2,687/3,246 = 83%). Review of the literature.

RESULTS

Infections of the patient and transplant rejection later in life are minor residual risks. Post-transfusion purpura was suspected once but not verified. Anaphylaxis or malignancy were not promoted. Fetal/newborn alloimmune disease (severe hemolytic disease, thrombocytopenia, neutropenia) were not observed.

CONCLUSION

Based on microbiological, immunological, and hematological testing the risks of intradermal LIT are low.

The Evolution of Alloimmunity and the Genesis of Adaptive Immunity

Infectious agents select for host immune responses that destroy infectious nonself yet maintain tolerance to self. Here we propose that retroviruses and other host-antigen associated pathogens (HAAPs) select for the genetic, biochemical, and cell biological properties of alloimmunity, also known as the histocompatibility or tissue rejection response. This hypothesis predicts the major observations regarding histocompatibility responses, including: (i) their existence in animals as diverse as sponges and humans; (ii) extreme polymorphism and balanced allele frequencies at histocompatibility loci, including the human MHC and blood group loci; (iii) the frequency dependent selection of histocompatibility alleles; (iv) the ancient age of many alloantigenic polymorphisms; (v) the high ratio of nonsynonymous mutations to synonymous mutations at histocompatibility loci; (vi) disassortative mating based on MHC alleles; (vii) the inability to explain the existence and continuing selection of histocompatibility alleles by other more conventional biochemical and genetic paradigms; and (viii) the susceptibility of HAAPs, particularly retroviruses such as HIV (human immunodeficiency virus), to histocompatibility reactions. In addition, the hypothesis that HAAPs select the forms and molecules of alloimmunity offers simple explanations for the evolution of histocompatibility systems over time, the initial selection of hypervariable immune mechanisms, and the genesis of adaptive immunity.

Testing for hematologic disorders and complications

This review summarizes state-of-the-art and emerging techniques in the antenatal diagnosis of fetal anemia and hemoglobinopathies. Fetal anemia may result from hemolytic disease, hemorrhage, suppression of erythropoiesis, infection (eg, parvovirus B19), or trauma. The clinical laboratory plays an essential role in the evaluation of these disorders by way of the use of various hematologic, biochemical, serologic, cytometric, and molecular genetics methods. Hemoglobinopathies are the most common class of single gene disorders worldwide. The authors have used the example of homozygous alpha-thalassemia major (Hb Barts disease) as a paradigmatic case for antenatal hemoglobinopathy screening. Perhaps the most familiar indication for hematologic screening in pregnancy is HDFN, most commonly in pregnancies previously sensitized to the RhD antigen. All pregnant women, regardless of their past medical or obstetric history or previous antibody screens, should have ABO/Rh blood typing and a red cell antibody screen performed at the first prenatal visit. Long-established methods for assaying FMH (KB method), microcytosis (hemogram with red cell indices), and blood group incompatibility (direct antigen test, serologies) remain critical for rapid, sensitive diagnosis. Analysis of fetal free DNA in maternal plasma holds the promise for rapid, ultrasensitive, and noninvasive detection of many fetal hematologic disorders.