Common Alloimmunization Misconceptions

Every day women and providers hear statements about alloimmunization, but not all of these  statements are correct! As monitoring and treatment options continue to evolve, the information that patients and providers share must also change. Below are some common misconceptions or myths that many alloimmunized patient have heard. See if you can tell which statements are true and which ones are false.

Rh Disease has been eradicated.


Rh disease has not been eradicated. Since the invention of Rh Immune Globulin (RhoGAM), sensitization rates for anti-D alloimmunization have plummeted - but anti-D alloimmunization still occurs. For some women, RhoGAM simply doesn’t work. Others are not given a high enough dose, or are not treated at the appropriate time. Since the number of women developing anti-D has decreased dramatically, alloimmunization to other antigens has become more common. Anti-K, anti-E, and anti-c are 3 clinically significant antibodies that are now most commonly found among pregnant women.

We know that HDFN affects 276 out of every 100,000 births globally. In 2019, there were more than 123,040,800 global births. We can estimate that about 339,593 infants around the globe were affected by HDFN in 2019 alone.

Rh Incompatibility
World Population


Antibodies do not all act in the same manner. Certain antibodies such as anti-K and anti-M attack and destroy the progenitor cells before they can become red blood cells. Some antibodies will attack antigens on the kidneys or suppress the bone marrow. Not only is there variation between the different antibodies, but between each individual pregnancy as well. The level of severity can be different in each patient. Some women with a titer of 2 may have a highly affected infant requiring IUTs, while others may have a titer of 128 and deliver and unaffected infant. To learn more about the unique differences between antibodies see HDFN and the Clinical Impact of Specific Antibodies.


The fetus can produce its own blood complete with the D antigen as early as 8 weeks. This is enough blood to sensitize some women, however it does not require a full dose of Rhogam. A partial dose, or a dose of MICRhoGAM may be used instead. According to the package insert, MICRhoGAM or RhoGAM should be used at any actual or threatened loss at any gestation. Even if a woman with a Rh negative blood type does not experience early miscarriage or bleeding, she should receive RhoGAM in their 28th week of pregnancy and again within three days of delivery.

“Each single dose prefilled syringe of MICRhoGAM contains 50 μg (250 IU) of Rho(D) Immune Globulin
(Human). This dose will suppress the immune response to up to 2.5 mL of Rh-positive red blood cells.
MICRhoGAM is indicated within 72 hours after acute or threatened termination of pregnancy up to and including 12 weeks gestation. At or beyond 13 weeks gestation, RhoGAM should be administered instead of MICRhoGAM.”

“Clinical studies demonstrated that administration of MICRhoGAM within three hours following pregnancy termination was 100% effective in preventing Rh immunization.”

RhoGAM for Health Care Providers


A first sensitized pregnancy absolutely can result in adverse outcomes in the fetus and infant. While some first affected pregnancies will be unaffected or only deal with hyperbilirubinemia and potential anemia after birth, other first affected pregnancies will require IUTs and can end in fetal/infant death if not properly managed. If titers are critical it is imperative to use regular MCA dopplers to assess for fetal anemia regardless of what number pregnancy it is.

Management of Pregnancies Complicated by RhD Alloimmunization
Management of Non-RhD Red Blood Cell Alloantibodies During Pregnancy


There are various interventions available for women with previously affected pregnancies that are relatively low-risk when managed by an experienced provider. The survival rate with skilled intrauterine transfusion is over 90% if hydrops is not present. For those women with severe cases, intravenous immune globulin combined with plasmapheresis has been used to delay HDFN in the fetus. Women with anti-K or anti-D who have a prior history of severe anemia or fetal loss <24 weeks can apply for the clinical trial of Nipocalimab (aka M281), a monoclonal antibody that blocks maternal antibodies from passing through the placenta and into the fetal circulation. Patients with heterozygous partners who wish to have more biological children may want to consider IVF with PGD.

In rare cases where a woman is unable to receive transfused blood cells, intravenous immune globulin combined with plasmapheresis has been used to successfully allow women to carry to term without severe anemia.

Intrauterine Fetal Transfusion of Red Cells
Treatment with Plasmapheresis and IVIG In Pregnancies Complicated with anti-PP1PK or anti-K Immunization
The role of preimplantation genetic diagnosis in the management of severe rhesus alloimmunization: first unaffected pregnancy: case report.
Clinical Trial for Nipocalimab
Clinical Trials For Alloimmunization and HDFN


Titers can increase at any time. It is especially common for them to increase in the third trimester as both maternal and fetal blood volumes increase and the chances of fetomaternal hemorrhage (FMH) are higher. Titers are commonly tested monthly until 28 weeks, biweekly until 36 weeks, and weekly until delivery. The increased frequency in testing comes as a result of the greater likelihood of increasing maternal titers and fetal anemia as gestation advances. Up-To-Date articles about alloimmunization state, “A woman's first pregnancy complicated by Rh(D) alloimmunization is managed differently from subsequent pregnancies because her anti-D titer is usually low at the beginning of her first affected pregnancy; severe fetal anemia may not develop or develops in the late second trimester or the third trimester.”

Management of Pregnancy Complicated by RhD Alloimmunization


Administration of RhoGAM or other RhD Immune globulin products is contraindicated if a woman has anti-D. Rhogam is used to prevent alloimmunization to the D antigen from happening. It does not treat alloimmunization. Women with anti-D are already alloimmunized and producing antibodies against the D antigen. They should not be given RhoGAM.


Fetal anemia requiring intrauterine transfusion can happen at 16 weeks or earlier. While the rate of complications is higher prior to 20 weeks gestation, both intraperitoneal and intravascular IUT are possible to treat severe anemia. Severe anemia can happen without signs of hydrops or ascites at early gestations. The survival rate for those treated with early IUT is 80% or higher. MCA PSV reference values are available beginning at 14-18 weeks gestation, and a recent study provided values as early as 12 weeks gestation.

Efficacy of Antenatal Intravenous Immunoglobulin Treatment in Pregnancies at High Risk due to Alloimmunization to Red Blood Cells
Management of Very Early Fetal Anemia Resulting From Red-Cell Alloimmunization Before 20 Weeks of Gestation
Early intrauterine transfusion in severe red blood cell alloimmunization
Normogram of Middle Cerebral Artery Doppler Indexes and Cerebroplacental Ratio at 12 to 14 Weeks in an Unselected Pregnancy Population
Middle cerebral artery peak systolic velocity for the diagnosis of fetal anemia: the untold story


MCA scans can begin as early as 12-16 weeks. IVIG and plasmapheresis can be started as early as 8 weeks gestation to help get the fetus to a gestational age that will allow for intrauterine transfusion to take place. Intrauterine transfusions can be done as early as 15 weeks via intraperitoneal transfusion (IPT), or as early as 18 weeks via intravenous transfusion (IVT). IPTs are not effective if the fetus already has ascites in the abdomen, so intervention before fluid build up is vital.

Link to Taiwan study with MCA PSV values at 14 weeks.

Intrauterine Fetal Transfusion of Red Cells
Management of Very Early Fetal Anemia Resulting From Red-Cell Alloimmunization Before 20 Weeks of Gestation
Early intrauterine transfusion in severe red blood cell alloimmunization
Therapeutic plasma exchange and intravenous immunoglobulin as primary therapy for D alloimmunization in pregnancy precludes the need for intrauterine transfusion


Especially at early gestations, it is possible for the fetus to be severely anemic without showing signs of ascites or hydrops. It is vitally important that MCA scans are performed to assess for fetal anemia and that ultrasound findings of fluid build up are not the sole indicator of anemia. The purpose of the MCA scan with IUT is to intervene before hydrops presents. After fetal hydrops is present, the survival rate plummets and adverse cardiovascular and neurological outcomes are more likely. In the event of an elevated MCA scan near 1.5, it is common practice for the patient to be rescanned within the next 1-2 days and prepped for an IUT if results are still elevated.

“Transfusion at a moderately reduced hemoglobin level results in a better fetal outcome than waiting until development of severe anemia (hemoglobin >7 g/dL below the normal mean for gestational age [35]) or hydrops (hemoglobin less than 5 g/dL).”

Management of Pregnancy Complicated by RhD Alloimmunization
Intrauterine Fetal Transfusion of Red Cells
Intrauterine Blood Transfusion: Current Indications and Associated Risks


Steroids falsely lower the PSV and thus the MoM value from an MCA scan. Administration of intramuscular or vaginal steroids before an IUT or delivery will show a lower MoM (an average of 0.3 lower) for 4 or more days without actually reducing the anemia. The anemic fetus will still be anemic despite improving values after steroid administration. Steroids are not a treatment for anemia and IUT should not be delayed due to a decreased PSV after steroids. In one study, a statistically significant decrease in fetal MCA-PI was noted after progesterone administration both vaginally and intramuscularly.

Antenatal corticosteroid therapy: a comparative study of dexamethasone and betamethasone effects on fetal Doppler flow velocity waveforms.
Effect of antenatal betamethasone therapy on maternal-fetal Doppler velocimetry.
The short term fetal cardiovascular effects of corticosteroids used in obstetrics
Effects of maternal dexamethasone administration on fetal Doppler flow velocity waveforms.
Vaginal versus intramuscular progesterone in the prevention of preterm labor and their effect on uterine and fetal blood flow


Women with alloantibodies are at high risk for hemolytic transfusion reactions (HTRs). Up to 50% of HTRs are due to existing antibodies. Blood must be closely matched to ensure that it is antigen negative. Blood should be on hand in case of FMH or delivery. Patients should be encouraged to tell their care providers that they have allo antibodies before any medical/surgical procedure so that matching donor blood can be ready during the procedure in case a transfusion is needed. Patients can get a medical alert card with their unique antibodies listed, that conveys the risk of hemolytic transfusion reaction. The need for special blood will continue throughout a woman’s lifetime. In some cases, the level of antibodies will even drop to undetectable levels - an event known as antibody evanescence. This does not mean that the patient is not still sensitized, or that the patient will not produce antibodies again. Upon an additional exposure, the body will rapidly reproduce the antibodies and levels will rise again in an event known as antibody boostering.

Hemolytic Transfusion Reactions
Risk of Hemolytic Transfusion Reactions Following Emergency-Release RBC Transfusion


Titers are not a direct indication of how a neonate will do after birth. A titer level below critical does not rule out mild or moderate anemia, but does suggest that severe anemia requiring IUT is unlikely. Some patients have more aggressive antibodies than others and although rare, severe fetal anemia has been documented with titer levels below critical. Infants with HDFN can still require phototherapy, exchange transfusion, and top up transfusions at 4-6 weeks even when the mother’s titer was below critical during the pregnancy. Anti-K specifically is notorious for not correlating severity of disease with titer level and has caused severe fetal anemia requiring IUTs at titers as low as 1. Multiple providers now suggest that there is no safe titer for anti-K. Maternal titers are not useful for predicting fetal anemia after the first affected pregnancy. Women who have had a previous affected pregnancy should automatically be monitored via MCA scans for anemia since they are more likely to be affected even with low titers. The prudent provider will carefully monitor both mother/fetus and the neonate for signs of HDFN and its related complications regardless of the maternal titer.

Anti‐E in pregnancy
Hemolytic Disease of the Newborn Treatment & Management
Management of Non-RhD Red Blood Cell Alloantibodies During Pregnancy
Management of Pregnancy Complicated by RhD Alloimmunization


In addition to anemia and hyperbilirubinemia, the two commonly known effects of HDFN, the neonate is at risk for developing neutropenia and thrombocytopenia as a result of maternal alloimmunization. Delayed onset anemia is a risk up to 12 weeks after birth. This is anemia that develops in a child with HDFN who is not initially anemic, and it can have fatal consequences if left untreated. It is common for infants with HDFN to need their first transfusion between 2 to 6 weeks of age. Prudent follow up testing includes weekly hemoglobin checks (or CBC) and the occasional reticulocyte count until the infant’s numbers are elevating on their own consistently without a blood transfusion.

Hematological morbidity and management in neonates with hemolytic disease due to red cell alloimmunization
Late onset neonatal anaemia due to maternal anti‐Ge: possible association with destruction of eythroid progenitors
Late onset neonatal anaemia due to maternal anti-Kpb induced haemolytic disease of the newborn


Iron supplements will not help infants with Hemolytic Disease of the Fetus and Newborn (HDFN), and can actually be dangerous in some instances. Infants with HDFN have hemolytic anemia, not iron-deficiency anemia. Infants with hemolytic anemia have normal iron stores, or high iron stores if they have had an intrauterine transfusion (IUT). Iron should never be prescribed for an infant with HDFN without first conducting a ferritin test.

Iron status in infants with alloimmune haemolytic disease in the first three months of life
M. E. A. Rath, V. E. H. J. Smits-Wintjens, D. Oepkes, F. J. Walther & E. Lopriore
"On the contrary, iron overload occurs in 70% of neonates with alloimmune HDFN at birth, 50% at the age of 1 month and 18% at the age of 3 months. Therefore, we advise to measure iron status, and we discourage the use of iron supplementation in the first 3 months of life in neonates with alloimmune HDFN. Haemolysis and intrauterine and postnatal transfusions probably both contribute to the high incidence of iron overload in alloimmune HDFN."
70% of iso babies had iron overload at birth, none were iron deficient at birth, 50% at 1 month had iron overload, and 18% had iron overload at 3 months. "There is a number of case reports published on the risk of severe iron overload, diagnosed by liver biopsies, following IUTs for Rh HDFN. These infants were all born at 33 or 34 weeks of gestation and received 2–5 IUTs and several postnatal transfusions. Their serum ferritin levels ranged from 2479 to 28 800 lg/l. In addition to transfusions for alloimmune HDFN, the haemolysis itself can also contribute to iron overload in alloimmune HDFN."

Additional articles:
Rhesus haemolytic disease of the newborn: Postnatal management, associated morbidity and long-term outcome.
A Case of Rhesus Hemolytic Disease With Hemophagocytosis and Severe Iron Overload Due to Multiple Transfusions


A patient may have a positive Indirect Agglutination Test for up to 6 months following administration of RhoGAM. The maximum concentration in the blood stream is 4 days, the half life is ~30 days, and the injection provides protection for 12 weeks. Positive IAT results after 6 months or with a titer over 16 indicate a true alloimmunization with anti-D has occurred. If a woman’s previous delivery and RhoGAM administration was >6 months ago, then true sensitization has occurred.


There are some maternal antibodies which are known to have a negative IAT and yet still produce an affected infant. These include: Anti-Dia (Diego Blood Group), anti-Jsa (Kell Blood Group), and anti-Wra (Diego Blood Group). With both anti-Dia and anti-Wra being in the Diego blood group, it is suspected that anti-Dib, another Diego blood group antibody may have a similar result, but it has not been reported. The degree of HDFN ranges from mild to fatal. Anti-Jsa has been reported to produce a negative maternal IAT despite producing a hydropic infant with a DAT strength of 3+.

Hemolytic disease of newborn infants caused by anti-Diego antibodies
Characterization of an anti‐Dia antibody causing hemolytic disease in a newborn infant
The first case of hydrops fetalis caused by anti-Jsa. A case report and suggestions on the antenatal diagnosis of hemolysis due to antibodies against rare antigens
A case of hemolytic disease in a newborn associated with anti-Wra (WRIGHT) antibodies
Clinical case of the month. Mild hemolytic disease of the newborn due to an anti-Wr(a) antibody
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