Factors Behind Decreased Red Cell Antibody and Hemolytic Disease of Fetus and Newborn Rates: Single Center Experience
Year: 2025
Type: article
Study design: Observational Study
Abstract: Hemolytic disease of the fetus and newborn (HDFN) is a life-threatening condition caused by maternal alloimmunization to red blood cell (RBC) antigens. Over the years, the introduction of preventive and therapeutic measures has significantly reduced the frequency of anti-D and non-D immunizations in pregnant women, leading to a decline in HDFN cases. The postnatal and antenatal administration of anti-D immunoglobulins has reduced the prevalence of anti-D antibodies in pregnant women to less than 0.5%.1 However, the relative importance of non-D antibodies has increased following the widespread adoption of immunoprophylaxis. Among non-D antibodies, those from the Rh system and anti-K antibodies are the most common causes of HDFN. Approximately 50% of pregnant women with non-D antibodies have a history of blood transfusions.2 Therefore, transfusing women of reproductive age with RBCs compatible with Kell, Rhc, RhE, and RhC antigens could further reduce the incidence of non-D antibodies and HDFN. At our center, women of reproductive age and female children have been transfused with Kell-negative RBCs since 2000, and since 2008, RBCs compatible with Rhc, RhE, RhC, and Rhe antigens have also been used. Additionally, we implemented a standardized algorithm for monitoring immunized pregnancies and referring cases for intrauterine transfusion (IUT) to a specialized center, alongside a restrictive approach to transfusion therapy for HDFN. The study was approved by the Ethics Committee of the University Hospital of Split (Ethical Approval Number: 520-03/24-01/109). Data collection and analysis were performed in compliance with the Declaration of Helsinki. This prospective study collected data over 14 years (2010–2023) on pregnant women, immunized women, and their offspring. The primary outcomes were the incidence of anti-D and non-D antibodies in pregnancies and severe HDFN caused by specific antibodies. Data were compared to a historical control group. The study was conducted at the University Hospital of Split, Croatia, the regional institution responsible for pregnancy care, monitoring of RBC-alloimmunized women, and delivery management in Split-Dalmatia County. In Croatia, RhD-positive pregnant women undergo antibody screening during the first trimester (12 weeks) and again at 34 weeks. RhD-negative women are tested at 12, 28, and 34 weeks of pregnancy, as well as immediately postpartum. Rh prophylaxis is administered to RhD-negative women following miscarriage, pregnancy termination, chorionic villus sampling, amniocentesis, and delivery. Between January 1, 2010, and December 31, 2023, there were 61,040 live births in Split-Dalmatia County. Clinically relevant RBC antibodies were detected in 198 pregnancies involving 180 women (14 of whom had more than one pregnancy during the study period). Multiple clinically relevant alloantibodies were found in 24 (12%) of these women. The incidence of anti-D antibodies in RhD-negative women was 0.96%, while the incidence of non-D antibodies in all pregnancies was 0.17%. The most frequently detected antibody was anti-D, followed by anti-c, anti-E, and anti-K as the most common non-D antibodies (Table 1). Table 1 - Prevalence of clinically significant alloantibodies in pregnant women tested between January 1, 2010 and December 31, 2023. Blood group system Specificity dominant alloantibodies n Incidence Rh Anti-D 94 Incidence per 100 RhD negative pregnant women 0.95*. Kell Anti-K 14 – Rh Anti-c 26 – Rh Anti-E 26 – Rh Anti-C 6 – Duffy Anti-Fy 9 – MNS Ss antibodies 6 – Kidd Anti-Jk 10 – Other Other antibodies 7 – Non-anti-D antibodies in total 104 Incidence per 100 pregnant women is 0.17†. *Anti-D antibody incidence denominator: 10,800 RhD-negative pregnant women tested.†Non-anti-D antibody incidence denominator: 61,040 pregnant women tested.Anti-D: Antibody against the D antigen in the Rh blood group system; Anti-K: Antibody against the K antigen in the Kell blood group system; Anti-c: Antibody against the c antigen in the Rh blood group system; Anti-E: Antibody against the E antigen in the Rh blood group system; Anti-C: Antibody against the C antigen in the Rh blood group system; Anti-Fy: Antibody against the Fy antigen in the Duffy blood group system; Ss antibodies: Antibodies against the S or s antigens in the MNS blood group system; Anti-Jk: Antibody against the Jk antigen in the Kidd blood group system; HDFN: Hemolytic disease of the fetus and newborn; Other antibodies: Antibodies against other blood group antigens not listed above; RhD: Rhesus D antigen; –: Not applicable. Of the 198 pregnancies with clinically significant antibodies, 14 were excluded due to missing data (neonatal antigen status or direct antiglobulin test (DAT)). Among the remaining 184 pregnancies, 132 neonates were antigen-positive, 95 had a positive DAT result, and severe HDFN was diagnosed in 30 cases. Of these, 26 were caused by anti-D antibodies, two by anti-K, and two by anti-c (Supplementary Table 1, https://links.lww.com/MFM/A69). No cases of perinatal death were recorded during the study period. The frequency of severe HDFN due to anti-D and non-D antibodies was 4.9 per 10,000 live births. Compared to the historical control (1993–2008),3 the incidence of severe HDFN decreased significantly (4.9/10,000 vs. 13.2/10,000, P < 0.001). An even more pronounced reduction was observed for severe HDFN caused by non-D antibodies (0.6/10,000 vs. 4.8/10,000 in the historical control, P < 0.001). The overall prevalence of anti-D antibodies varies across different racial and ethnic groups. Individuals of European descent (16%) tend to have RhD-negative blood types more frequently than those of African (5% to 8%), Indian (5%), Asian (1% to 2%), or Native American (1% to 2%) descent.4 In Croatia, the prevalence of RhD-negative blood type is 18%.3 In this study, the frequency of anti-D antibodies in RhD-negative pregnant women was 0.95%, compared to 1.3% in the historical control group. This frequency is similar to that reported in other populations of European descent who practice postnatal immunoprophylaxis, as is done in our country.1 The decreased incidence of RhD immunizations compared to the historical control3 can be attributed to the consistent implementation of postnatal immunoprophylaxis. Since 2000, women of reproductive potential and female children in our center have been transfused with Kell-negative RBCs, and since 2008, they have also received C, c, E, and e antigen-compatible RBCs.2 This has led to a decrease in non-D antibodies in pregnant women. The total incidence of non-D immunizations in this study was 0.17%, compared to 0.2% in the historical control.3 The most significant decrease was observed in anti-K antibodies in pregnancy, with 14 cases out of 61,040 versus 45 cases out of 85,600 in the historical control. This can be explained by the established practice of Kell antigen-compatible transfusions for women younger than 50 years of age. The prevalence of non-D antibodies in our population is comparable to regional studies in Sweden and the Netherlands, which show a prevalence of about 0.2% in pregnant women. The frequency of maternal alloimmunization by clinically relevant non-D antibodies in other studies has been observed to range from 0.15% to as high as 6.2%.1 This variation in prevalence can be attributed to the lack of a clear definition of “the presence of clinically relevant non-D antibodies,” heterogeneity in screening protocols, and the use of preselected high-risk study populations with an unknown relation to the general population of pregnant women.1 Delaney et al.5 found that the incidence of severe HDFN is influenced by several factors, but particularly by the diversity of criteria used to label HDFN as severe. Therefore, population studies with the same approach to prevention, diagnosis, and treatment of HDFN report different incidence rates across different centers (ranging from 3 to 80 per 10,000). de Winter et al.4 found significant differences in the rates of exchange transfusions and simple RBC transfusions between centers and countries. The strengths of this study include the use of consistent criteria for defining severe HDFN and a very large sample size across two different periods. In this study, the incidence of severe HDFN has decreased significantly from 13.2 per 10,000 in the historical control to 4.9 per 10,000. There were no recorded cases of perinatal death among children born to alloimmunized mothers, in contrast to the historical control, where eight cases of perinatal death due to HDFN were confirmed.3 Clearly, the follow-up of high-risk pregnancies and timely treatment with IUTs have been more meticulous in recent years. The lower incidence of HDFN in this study is partly due to the lower incidence of maternal immunization, but also due to modified criteria for transfusion treatment. In this study, 30 out of 132 antigen-positive children (23%) classified as having severe HDFN and were treated with transfusions (IUTs, exchange transfusions, or simple blood transfusions), compared to 111 out of 267 antigen-positive children (41%) in the historical control. The criteria for transfusion management of HDFN (exchange transfusions and simple blood transfusions) are more restrictive in newer recommendations.6 In addition to restrictive transfusion practices, stricter adherence to phototherapy recommendations also reduced the need for exchange transfusions. Lower phototherapy threshold levels for HDFN are recommended, especially for younger gestational ages, to prevent manifestations of bilirubin encephalopathy, as well as a pre-discharge risk assessment plan.6 Additional modulators of the disease course include intravenous immunoglobulins and supportive care measures with close monitoring of metabolic changes. Uniform criteria for clinically relevant RBC antibodies and severe HDFN are recommended for comparing the frequency of these conditions across different centers and countries. When comparing the results of this study with the historical control, we used the same criteria and found a statistically significant decrease in severe HDFN. The factors contributing to these results include compatible transfusions with Rh/Kell phenotype for women younger than 50 years of age, consistent implementation of the IUT algorithm, stricter adherence to phototherapy recommendations to reduce the need for exchange transfusions, and restrictive transfusion practices for simple blood transfusions. Since several measures were applied during the monitored period, the individual significance of each measure for the reduction in the number of immunizations and severe HDFN cannot be determined. Funding None. Conflicts of Interest None. Data Availability All data generated or analyzed during this study are included in this published article and its supplementary information files.
Source: Maternal-Fetal Medicine
Institutions: Klinički Bolnički Centar Split, University of Split
Language: English
Topic: Blood groups and transfusion
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: diamond
OpenAlex ID: W4408676168