Hemolytic Disease of the Fetus and Newborn (HDFN)

Hemolytic disease of the fetus and newborn (HDFN), also known as erythroblastosis fetalis or alloimmune HDFN, is a rare, immune-mediated blood disorder, in which maternal immunoglobulin G (IgG) antibodies cause the destruction of red blood cells (RBCs) in a fetus or neonate. It occurs when fetal RBCs express certain antigens that are not produced in the mother, then cross the placenta, and enter the mother’s blood. This causes isoimmunization, which is a production of maternal antibodies that is reactive to this exposure. The fetal RBCs are destroyed by this antibody reaction, which causes hemolysis, bilirubin release, and anemia. The strength and amount of antibody production by the mother, the fetus’ gestational age, and the fetus’ capacity to replace lost RBCs and eliminate bilirubin are some of the variables that affect the severity of the disease.¹ 

Laboratory and imaging tests are required to diagnose and treat pregnant women with HDFN. Rapid and marked hyperbilirubinemia or persistent hyperbilirubinemia, as well as hemolysis seen on blood film findings, are clinical indicators of HDFN. The severity of the disease is determined by the level of hematopoiesis.² 

Routine Blood Group Typing and Antibody Screening

During the initial prenatal appointment with a general physician, blood samples should be tested for antibodies and ABO and RhD blood group typing. This typing can identify RhD-negative women who produce anti-D antibodies. Regardless of whether the mother is RhD positive or RhD negative, antibody screening can identify those who have already generated alloantibodies in the first trimester.³ 

For RhD-negative women with a negative first trimester antibody screening, routine noninvasive fetal antenatal RhD screening is offered at 25 weeks gestational age, and repeat routine antibody screening is done for RhD-negative women only.³ 

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Hematology Testing for HDFN

Patients frequently exhibit anemia, thrombocytopenia, and neutropenia. Arteriolar samples can be utilized to assess anemia rather than those taken from capillary blood. Most often, neutropenia is seen following intrauterine transfusion. It is frequently accompanied by reticulocytosis and higher levels of circulating cytokines. Additionally, erythroblasts, polychromasia, anisocytosis, and the absence of spherocytes are frequently seen on peripheral blood smears. Exchange transfusions are frequently accompanied by thrombocytopenia. This occurs when blood platelets do not form properly and erythropoiesis takes precedence over platelet production.² 

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Serological Testing for HDFN

ABO and RhD blood typing, as well as an indirect antiglobulin test (IAT) to identify IgG antibodies, should be conducted on all pregnant women.⁴

IAT is utilized to find any unbound RBC antibodies in the patient’s serum. Native RBCs are taken out of the isolated serum. After that, foreign RBCs with known antigenicity are incubated with the isolated serum sample. The presence of agglutination after the addition of the antiglobulin reagent denotes a positive test.⁵ 

During the first prenatal appointment, if the antibody screen for Rh is positive, a titer is also assessed. Fetal hydrops has been linked to antibody titers of 1:16 and higher. Blood type testing on the father can be done to identify whether the fetus is at risk. The safest approach is to treat every pregnancy as if the fetus is at risk because around 5% of all pregnancies have unknown or erroneous paternity.¹ 

Antibody titers should be measured approximately every 4 weeks during pregnancy. If they are below 1:16, pregnancy can be managed as usual. If they surpass 1:16, however, serial amniocentesis should begin as early as 16 to 20 weeks. Fetal cells from the initial amniocentesis sample can be taken and checked for the Rh antigen to assess fetal Rh status. If the test is negative, the pregnancy can be monitored in a usual manner.¹ 

After birth, the direct Coombs test or direct agglutination test (DAT) is used to determine the presence or absence of HDFN. The purpose of this test is to detect alloantibodies in the infant’s blood. Babies with elevated bilirubin levels often undergo additional testing using a DAT to ascertain the underlying cause.⁶

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Imaging Studies for HDFN

Once Rh positivity in the fetus has been confirmed, repeated maternal pelvic ultrasounds and umbilical artery and middle cerebral artery (MCA) dopplers can be used for fetal monitoring. MCA dopplers are frequently used to check Rh-positive fetuses for anemia. From the 24th week of pregnancy, they are performed every 1 to 2 weeks to measure peak systolic velocity (PSV), which increases with anemia. If the fetus is severely afflicted, fetal ultrasounds are typically used to screen for ascites, soft-tissue edema, scalp edema, pleural effusion, hepatomegaly with portal hypertension, and cardiomegaly.² 

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Direct Fetal Genotyping for HDFN

Serological reagents do not precisely identify the RhD type in certain cases, such as in weak D phenotypes. For these individuals, blood typing can also be done using molecular techniques.⁴ Direct fetal red cell genotyping is an option for the evaluation of fetal blood group expression to predict the fetal risk of developing HDFN in sensitized mothers. Fetal DNA is obtained via amniocentesis, chorionic villus sampling, or the collection of cell-free fetal DNA from maternal plasma.^4,7 

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References

1. Nassar GN, Wehbe C. Erythroblastosis fetalis. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2023. Updated June 26, 2023. Accessed August 30, 2023.
2. Myle AK, Al-Khattabi GH. Hemolytic disease of the newborn: a review of current trends and prospects. Pediatric Health Med Ther. 2021;12:491-498. doi:10.2147/PHMT.S327032
3. Dziegiel MH, Krog GR, Hansen AT, et al. Laboratory monitoring of mother, fetus, and newborn in hemolytic disease of fetus and newborn. Transfus Med Hemother. 2021;48(5):306-315. doi:10.1159/000518782
4. Delaney M, Matthews DC. Hemolytic disease of the fetus and newborn: managing the mother, fetus, and newborn. Hematology Am Soc Hematol Educ Program. 2015;2015:146-151. doi:10.1182/asheducation-2015.1.146 
5. Theis SR, Hashmi MF. Coombs test. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2023. Updated September 12, 2022. Accessed August 30, 2023.
6. Hemolytic disease of the fetus and newborn/maternal alloimmunization. Fetal Health Foundation. Accessed August 30, 2023.
7. British Committee for Standards in Haematology Blood Transfusion Task Force; Gooch A, Parker J, Wray J, Qureshi H. Guideline for blood grouping and antibody testing in pregnancy. Transfus Med. 2007;17(4):252-262. doi:10.1111/j.1365-3148.2007.00767.x

Reviewed by Debjyoti Talukdar, MD, on 8/6/2023.

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Harshi Dhingra, MD

Harshi Dhingra is a licensed medical doctor with specialization in Pathology. She is currently employed as faculty in a medical school with a tertiary care hospital and research center in India. Dr. Dhingra has over a decade of experience in diagnostic, clinical, research, and teaching work, and has written several publications and citations in indexed peer reviewed journals. She holds medical degrees for MBBS and an MD in Pathology.