Identification and management of fetal anemia due to hemolytic disease

Erythrokinetic mechanism(s) causing the "late anemia" of hemolytic disease of the fetus and newborn

A transfusion-requiring "late anemia" can complicate the management of neonates convalescing from hemolytic disease of the fetus and newborn (HDFN). This anemia can occur in any neonate after HDFN but is particularly prominent in those who received intrauterine transfusions and/or double-volume exchange transfusions. Various reports describe this condition as occurring based on ongoing hemolysis, either due to passive transfer of alloantibody through breast milk or persistence of antibody not removed by exchange transfusion. However, other reports describe this condition as the result of inadequate erythrocyte production. Both hypotheses might have merit, because perhaps; (1) some cases are primarily due to continued hemolysis, (2) others are primarily hypoproductive, and (3) yet others result from a mixture of these two mechanisms. We propose prospective collaborative studies that will resolve this issue by serially quantifying end-tidal carbon monoxide. Doing this will better inform the assessment and treatment of neonates recovering from HDFN.

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.

Intrauterine Transfusion for Rhesus Alloimmunization: A Historical Retrospective Cohort from A Single Reference Center in Brazil

Objective: This study aimed to describe the historical experience of a single reference center in Brazil with intrauterine transfusion (IUT) for Rhesus (Rh) alloimmunization, evaluating the major complications and the perinatal outcomes of this procedure. Methods: This retrospective cohort study evaluated data from medical records of pregnant women between 20 and 34 weeks of gestation whose fetuses underwent IUT by cordocentesis between January 1991 and June 2021. The same experienced examiner performed all procedures. Univariate and multivariate logistic regression was used to assess the effect of fetal hydrops, duration of IUT, post-transfusion cord bleeding time, and bradycardia on death (fetal or neonatal). Results: We analyzed data from 388 IUTs in 169 fetuses of alloimmunized pregnant women with a mean age of 29.3 ± 5.1 years. Death and fetal hydrops were significantly associated at first IUT (p < 0.001). We had two cases of emergency cesarean section (mean of 0.51% per IUT) and three cases of premature rupture of the ovular membranes (mean of 0.77% per procedure). Thirty-six deaths were recorded, including 14 intrauterine and 22 neonatal. A higher percentage of neonatal deaths was observed in the group with post-transfusion cord bleeding time > 120 s (45.8%). The odds of neonatal death were 17.6 and 12.9 times higher in cases with hydrops and bradycardia than in cases without hydrops and bradycardia, respectively. The odds of death (fetal and neonatal) were 79.9 and 92.3 times higher in cases with hydrops and bradycardia than in cases without hydrops and bradycardia, respectively. Conclusions: The most common complications of IUT for Rh alloimmunization were post-transfusion cord bleeding, fetal bradycardia, premature rupture of ovular membranes, and emergency cesarean section. The IUT complication most associated with death (fetal and neonatal) was bradycardia, and the perinatal outcomes were worse in fetuses with hydrops.

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.

History and current standard of postnatal management in hemolytic disease of the fetus and newborn

Since the discovery of the Rh blood group system in 1940, a greater understanding of hemolytic disease of the fetus and newborn (HDFN) was gained. In the years thereafter, researchers and clinicians came to the current understanding that fetal and neonatal red blood cells (RBC) are hemolyzed by maternal alloantibodies directed against RBC antigens potentially leading to severe disease. Preventative measures, such as Rhesus(D) immunoprophylaxis (RhIG), have greatly decreased the prevalence of Rh(D)-mediated HDFN, although a gap between high-income countries and middle- to low-income countries was created largely due to a lack in availability and high costs of RhIG. Other important developments in the past decades have improved the identification, monitoring, and care of pregnancies, fetuses, and neonates with HDFN. Prenatally, fetal anemia may occur and intrauterine transfusions may be needed. Postnatally, pediatricians should be aware of the (antenatally determined) risk of hemolysis in RBC alloimmunization and should provide treatment for hyperbilirubinemia in the early phase and monitor for anemia in the late phase of the disease. Through this review, we aim to provide an overview of important historic events and to provide hands-on guidelines for the delivery and postnatal management of neonates with HDFN. Secondarily, we aim to describe recent scientific findings and evidence gaps.

CONCLUSION

 Multiple developments have improved the identification, monitoring, and care of pregnancies and neonates with HDFN throughout the centuries. Pediatricians should be aware of the (antenatally determined) risk of hemolysis in RBC alloimmunization and should provide treatment for hyperbilirubinemia in the early phase and monitor for late anemia in the late phase of the disease. Future studies should be set in an international setting and ultimately aim to eradicate HDFN on a global scale.

WHAT IS KNOWN

• Developments have led to a greater understanding of the pathophysiology, an improved serological identification and monitoring of at-risk cases and the current pre- and postnatal treatment.

WHAT IS NEW

• This review provides the pediatrician with hands-on guidelines for the delivery and postnatal management of neonates with HDFN. • Future studies should be set in an international setting with the ultimate aim of eradicating HDFN.