Alloimmunization occurs when a patient is exposed to foreign red blood cell antigens, and subsequently develops antibodies against one or more foreign antigens. This exposure most commonly occurs through pregnancy, blood transfusion or shared needles. For patients without childbearing potential or who are not currently pregnant, the only clinical impact of this antibody development is the patient’s risk for a hemolytic transfusion reaction. It is for this reason that the presence of antibodies is usually discovered during blood group matching in anticipation of transfusion or in early pregnancy during standard first trimester screening.
Clinically significant antibodies have the potential to lyse fetal and newborn red blood cells (RBCs) causing mild to severe hemolysis. This can result in hemolytic disease of the fetus and newborn (HDFN) presenting from mild anemia and icterus to hydrops fetalis, a condition leading to edema and heart failure in the fetus. Though maternal alloimmunization is a serious and nuanced condition, close monitoring and prompt clinical intervention results in a high survival rate for the child of an alloimmunized woman.
Alloimmunization occurs in approximately one to two percent of pregnancies 1, though this estimate includes antibodies which are not clinically significant (see Appendix A for a table of clinically significant antibodies). A recent retrospective observational study by Sánchez-Durán et al. in a large university setting identified maternal antibodies in 337 pregnancies in a fifteen-year period, of which 259 were clinically significant and known to have the potential to cause mild to severe hemolysis. Of these 259, the fetus was determined to be at risk (i.e., the fetus did inherit or had the potential to inherit the antibody’s target red blood cell antigen) in 194 2.
Though RhD immune globulin (RhiG) prophylaxis is standard in developed countries, Anti-D remains one of the most frequently identified antibodies (hence the name “Rh Disease”) along with Anti-Kell (Anti-K) and Anti-E. The distribution of clinically significant antibodies identified by Sánchez-Durán and colleagues can be found in Appendix B.
All pregnant patients should receive blood typing and an antibody screen (indirect Coombs test) during their first prenatal visit. The results of these screens present the following options for clinical management:
Once a patient’s antibody type and titer is established, the following sequence must take place to determine whether the fetus is at risk:
If the mother is alloimmunized against an antibody known to cause HDFN (Appendix A) and paternal antigen testing determines that the fetus may inherit the corresponding antigen (i.e., the fetus is “at risk”), antibody titers must be drawn at four-week intervals until 28 weeks, then every two weeks until they reach a critical titer (1:16 or 16 in most institutions, 1:4 or 4 for Kell). The critical titer reflects the threshold at which the antibody is capable of causing anemia requiring intervention in-utero. Important caveats include:
Once a critical titer is reached, titer concentration is no longer indicative of severity of HDFN. Noninvasive testing should be initiated weekly (or more frequently if rising or approaching 1.5 multiples of the median (MoM)) beginning at 16 to 18 weeks gestation 15 with doppler scanning of the fetal middle cerebral artery peak systolic velocity (MCA-PSV).The ideal MCA scan is performed by trained personnel during a state of fetal rest, in the absence of fetal breathing, and with no-minimal angle correction. Multiple readings should be obtained despite fetal activity level. Correct technique is critical in determination of the PSV value. The highest PSV value of at least three assessments should be recorded and used for clinical decision making. Read more about MCA technique here.
Note that the objective of the MCA-PSV scan is to detect fetal anemia in order to initiate intervention before progression to fetal hydrops. An MCA-PSV at or above 1.5 MoM for gestational age (calculator available at https://medicinafetalbarcelona.org/calc/), indicates possible severe anemia requiring intervention. Some types of steroid administration including oral 8, vaginal 8, or IM administration 9, can falsely lower an MoM score – leading to an anemic fetus being missed 35, 36. Steroids should only be administered after the decision to transfuse or deliver has been made. A planned intrauterine transfusion should not be modified based on MoM values observed after administration of steroids.
In addition to false lows, MCA scans have a false positive rate of 12% 11. Potential causes for falsely elevated MoM scores (scan indicates anemia when no anemia is present) include: fetal activity 10, fetal breathing 11, and maternal meals 12. For this reason, an MCA-PSV closely approaching 1.5 MoM should be reassessed in 2-3 DAYS 5, 15.
Some institutions initiate weekly antenatal testing (non-stress tests and biophysical profiles) at 32 weeks gestation for any at risk pregnancies regardless of titer and MoM 14, and this is suggested in recent UpToDate guidance 5.
Plasmapheresis or therapeutic plasma exchange (TPE) and intravenous immunoglobulin (IVIG) has been used for over 40 years to lower antibody titers and prevent/reduce fetal hemolysis in cases of extremely high titers or previous pregnancy loss as a result of HDFN. These interventions are most effective when initiated during the first trimester of pregnancy, typically around ten to twelve weeks of gestation. These usually are not effective in reducing fetal anemia once it is present, but these measures have been shown in small studies to reduce the time to initiation of IUT.
The mechanism of action of IVIG is not well-known in this application, though positive results have been demonstrated in small series and one prospective study 23, 24. This treatment usually initiates at 1g/kg maternal weight every week.
Plasmapheresis (removal of maternal plasma through an apheresis machine) may enhance the efficacy of IVIG, and though IVIG is sometimes instituted alone, plasmapheresis is not often instituted alone 25, 26. The combination of plasmapheresis and IVIG is typically reserved for the most high-risk cases due. A case series of 9 pregnancies using this technique reported reduced antibody titers, IUT initiation at a later gestation, and no fetal and neonatal fatalities 26. A common treatment plan for a patient receiving plasmapheresis and IVIG involves initiating several serial plasmapheresis treatments followed by IVIG at ten to twelve weeks’ gestation and continuing with weekly IVIG 26, though this should be considered case-by-case.
To read more about IVIG and plasmapheresis click here.
Erythropoietin is not commonly given to the mother for the treatment of alloimmunization. It is used in the few rare cases when women cannot be transfused with blood products or may need to donate their own blood. For additional information see “Religious objections to blood products”.
A clinical trial is currently ongoing for nipocalimab administered via weekly IV infusion in women who have previously had severely affected pregnancies and who have Anti-D or Anti-K antibodies. Visit the official site to assess the patient’s eligibility for this trial. Other trials relating to alloimmunization and HDFN can be found here.
After an MCA-PSV at or above 1.5 MoM, the following interventions should be scheduled within 2-3 days 6, 10 and conducted during the same session6:
The use of maternal premedication for IUT varies by center and may include use of local anesthetics, indomethacin/pethidine/promethazine, or spinal epidural analgesia. The prophylactic use of antibiotics or corticosteroids are sometimes used but their necessity is not well-established 18, 19. Premedication for the fetus is necessary in most cases including atracurium or vecuronium 6, 21 for fetal paralysis. Some practitioners recommend fentanyl for fetal pain 20 though it is not universally used 22. Click here for more detailed information about medications during IUTs.
Intrauterine transfusion should be guided by continuous ultrasound and staffed, at minimum, by an experienced maternal fetal medicine (MFM) specialist/perinatologist, seasoned ultrasonographer and one or more operating nurses. Inclusion of a neonatologist and/or additional MFM/perinatologist and support staff is not unwarranted. Transfusion volume can be calculated using a simplified formula by Giannina et al29 to attain 45% hematocrit 30, 31. Fetal hemoglobin testing through cordocentesis at the time of intravascular transfusion allows for a precise calculation of transfusion quantity. It is important to note that transfusing too large of a volume of blood can be dangerous. Fetal hematocrit should never be raised higher than 3x the beginning value.
For IVT, “transfusion volume = 0.02 × target increase in fetal Ht per 10% × g of estimated fetal weight, assuming that donor blood hematocrit is approximately 75%.” 16
For IPT, transfusion volume (mL) = (Gestation – 20) x 10. Blood in the peritoneal reservoir will be absorbed over 7-10 days.
The goal of an intrauterine transfusion is to maintain the fetal hematocrit above 25% . To this end, physicians will typically transfuse 10 days after the first transfusion, 2 weeks after the second transfusion, and 3 weeks after the third transfusion. Beyond the third transfusion, additional transfusions typically take place at 3-4 week intervals due to suppression of fetal erythropoiesis and the high percentage of donor RBCs which are safe from hemolysis. A second approach to the timing of intrauterine transfusions is to expect a decline in hemoglobin of 0.4 g/dL/day after the first transfusion, 0.3 g/dL/day after the second transfusion, and 0.2 g/dL/day after the third transfusion. This approach requires caution due to a potentially inaccurate fetal hemoglobin immediately after the procedure as a result of fetal fluid shifts, and bleeding from the puncture site 6. Information regarding the accuracy of MCA-PSV for determining the timing of additional transfusions is mixed, and providers must familiarize themselves with the various data available 61, 62, 63, 64, 65.
Fetal survival has increased in recent years following the incorporation of continuous ultrasound and clinical implementation and discussion of published research techniques. Even so, a large cohort study examining the outcomes of intrauterine transfusion found that 1.8% of fetuses died from the procedure even under the care of an experienced practitioner 16. A representative summary of fetal survival from Zwiers et al. is available in Appendix C 16. Additional IUT-related complications include bleeding from the puncture site, cord occlusion, brady- or tachycardia, Chorioamnionitis, and preterm premature rupture of the membranes (PPROM) which may require emergency caesarian or lead to maternal and fetal morbidity or mortality 32. For this reason IUTs performed at or after viability are usually performed in an operating suite where delivery may be carried out immediately. Normal neurologic outcome occurs in 94-95.2% of cases after IUTs. Severe hydrops may be associated with a higher risk of impairment 71, 72. The incorporation of IUT into a provider’s clinical practice should be weighed heavily against experience and available resources. Please contact the Allo Hope Foundation for referral recommendations to an experienced facility if patient need requires.
Additional information regarding IUT technique is available here.
After the last IUT, phenobarbital is considered in many institutions to enhance the fetus’ liver function and therefore accelerate the breakdown of bilirubin in neonatal circulation. In one study, mothers took 30mg phenobarbital three times daily after their last IUT until delivery. The incidence of exchange transfusion was significantly lower in neonates whose mothers took phenobarbital in advance of delivery 27. Due to the time required for phenobarbital to work, this intervention was not shown to be efficacious when administered to the neonate after delivery in a randomized controlled trial 28.
In at risk pregnancies with nonsignificant titers or MCA-PSV values consistently below 1.5MoMs, mild to no anemia can be presumed, therefore necessitating delivery at 37 to 38 weeks gestation 3.
There is an increased risk of false high MoM values beyond 35 weeks of gestation 10. It is generally agreed that a high MoM at or beyond 35 weeks of gestation merits delivery. In a pregnancy requiring IUTs, it is generally planned to conduct the final IUT at approximately 33-35 weeks with delivery planned at 35-37 weeks gestation.
Follow additional protocols regarding steroid administration and other preventative treatments in advance of preterm delivery. Be aware that steroid administration has been shown to falsely lower MoM values 8, 9, 35, 36 and planned delivery should not be modified based on MoM values observed after administration of steroids.
As part of a delivery plan, the MFM should connect the patient with services such as a NICU tour, a consultation with a pediatric hematologist, and a neonatologist after birth. Infants with HDFN should not be discharged from the hospital until a hematology appointment has been made. This will ensure proper follow up care for neonates exposed to maternal alloantibodies.
Among 106 patients in a single center in their first alloimmunized pregnancy with Anti-D, 57% did not develop a critical titer. Of those who did develop a critical titer, 54% developed HDFN of any severity, 26% developed severe disease (hydrops, fetal demise, need for IUT), 4% developed moderate disease (need for neonatal exchange transfusion), and 24% developed mild disease (need for phototherapy or simple blood transfusion 37).
Another recent 15-year retrospective study in a single center observed an IUT rate of 77% among at risk pregnancies with critical titers and MoMs above 1.5. The average gestational age at birth for this group was 34 weeks. Among those with critical titers but MoMs below 1.5, no IUT was required and the average gestational age at birth was 37 weeks 2.
With appropriate monitoring and skilled intervention, fetal survival rate has increased in recent years. The table below provides survival outcomes in a range of populations and treatment circumstances at some of the most experienced fetal centers in the world.
|Author, Year||Country, Time period||Population||Treatment Summary||Fetal/infant survival rate|
|Bondagji, 2012 42||Saudi Arabia, 2004-2009||84 pregnancies with C/c, D, and/or e antibodies with critical titers at first assessment (>16).||Routine ultrasound and amniocentesis prior to 2007, then MCA-PSV. IUT in 5 cases.||75%|
|Nardozza, 2007 43||Brazil, 1995-2004||99 pregnancies with D antibodies and critical titers (>16).||1995-2000: Amniocentesis between 26-28 weeks with subsequent amniocenteses based on results of first exam and ultrasonographic signs of fetal compromise. IUT if moderate to severe anemia prior to 34 weeks.
2001-2004: Weekly MCA PSV. IUT if moderate to severe anemia prior to 34 weeks.
|Overall (N=99): 76%
1995-2000 Amnio group (N=74): 73%
2001-2004 MCA group (N-25): 84%
|Sanchez-Duran, 2019 2||Spain, 2002-2017||57 pregnancies with at risk-fetuses and critical titers (>16) or Kell pregnancies of any titer requiring IUTs.||Fetuses being monitored through weekly MCA scans and IUTs performed through 34 weeks (or delivery if later).||84%|
|Dodd, 2018 41||Australia, New Zealand, Canada, UK, Ireland, Belgium, Argentina, 2009-2013||71 pregnancies with reported IUTs due to maternal alloimmunization||Half of pregnancies being monitored by fetal hematocrit, others by MCA-PSV (no significant difference between groups) and receiving IUTs.||88%|
|Tiblad, 2011 39||Sweden, 1990-2010||84 pregnancies with at-risk fetuses and critical titers (>64) requiring IUTs||Fetuses being monitored through “intermittent” MCA scans requiring subsequent IUTs.||92%|
|Sanchez-Duran, 2019 2||Spain, 2002-2017||93 pregnancies with at risk-fetuses and critical titers (>16) or Kell pregnancies and MCA-PSV scores below 1.5 MoM||Fetuses being monitored through weekly MCA scans, delivery at 37-39 weeks.||96%|
|Zwiers, 2017 16||Netherlands, 1988-2015||334 fetuses undergoing 937 intrauterine transfusions in 2001-2015||Fetuses with severe anemia requiring and receiving intrauterine transfusion.||97%|
|Pasman, 2015 40||Belgium, 2000-2014||56 pregnancies with reported IUTs due to maternal alloimmunization||Fetuses receiving IUTs.||100%|
|Sanchez-Duran, 2019 2||Spain, 2002-2017||38 pregnancies with at-risk fetuses and non-critical titers (<16).||Fetuses being monitored through titers every four weeks or every two weeks if rapidly increasing.||100%|
Estimates above reflect the positive impact of close monitoring of titers, frequent MCA-PSV doppler ultrasound, and prompt initiation of IUTs. Studies reporting lower survival rates also show practice standards not consistent with current recommendations.
Note as well the significance of RhIG prophylaxis and the importance of administering during early pregnancy bleeding, at the beginning of the third trimester and within 72 hours of birth to a RhD positive fetus. Bondaghi 42 reported that in Saudi Arabia between 2004 and 2009, failure to administer RhIG was common and 24% of women who were RhD negative became sensitized, a glimpse of the effect of sub-optimal monitoring and management of the RhD negative pregnant woman.
After birth, the risk of hyperbilirubinemia increases substantially because of the immature development of the neonatal liver’s metabolic pathways44. Phototherapy treatment may result in the development of Bronze Baby Syndrome in infants with elevated direct bilirubin levels. Bronze Baby Syndrome may increase the risk of complications due to hyperbilirubinemia such as Kernicterus 59. In addition to bronze baby syndrome, cholestasis occurs in up to 13% of infants with HDFN 58. Maternal antibodies may remain in fetal circulation for up to twelve weeks. Due to the risk of delayed onset anemia, follow-up in newborns whose cord blood confirms the presence of maternal antibodies is essential for twelve weeks, even in the absence of visible indications of anemia.
Immediately after delivery, obtain a cord blood sample before clotting for blood group assessment and Direct Agglutination Test (DAT)/Direct Coombs Test. An Indirect Agglutination Test (IAT) or antigen phenotype should be run in the case of maternal alloantibodies that have been shown to yield an affected infant despite a negative DAT. These include anti-C, anti-c, anti-Fya, anti-Good, anti-H, anti-Jra, anti-M, and anti-Mta antibodies. To read more about these exception antibodies see, “Direct Agglutination Test (DAT) Exceptions”.
Cord blood bilirubin and a complete blood count should also be ordered including hemoglobin, hematocrit, neutrophil count, thrombocyte count and reticulocyte count. Even in the absence of a positive DAT/IAT result, it is advised to continue to monitor bilirubin in the infant every four to six hours for at least the first 24 hours of life. If bilirubin levels are higher than expected during the infant’s first week of life, repeat the DAT. Establish hemoglobin and hematocrit values at eight to twelve hours of age and until stable.
Infants with HDFN should be considered to have “risk factors” when assessing bilirubin levels using standard phototherapy eligibility guidelines 45 as shown in Appendix D. An additional resource detailing presentation of early, late, and late hyporegenerative anemia in infants with HDFN can be found in Appendix E.
It is important to note that neonates who received IUTs in utero, the infant’s blood type and the state mandated newborn screenings may be incorrect due to the presence of donor blood. In this case, it is the donor’s blood being tested, not the infants.
Intervention may include phototherapy based on cord bilirubin and rate of rise. A cord bilirubin of ⩾2.05 mg/dl (pre-term) to 2.15 mg/dL (full-term) indicates need for phototherapy 60. Serum bilirubin should be assessed regularly during phototherapy. Exchange transfusion should be conducted if bilirubin reaches critical levels.
The implementation of intravenous immune globulin (IVIG) in the newborn is a promising noninvasive treatment which may reduce the rate of exchange transfusion but has not been shown to reduce the rate of top-up transfusion 46. Early studies indicated that high-dose IVIG (0.5g/kg IV immediately after HDFN is confirmed) does reduce serum bilirubin levels and subsequent need for exchange transfusion 47. A recent meta-analysis confirmed these findings in studies where IVIG doses ranged from 0.5g/kg to 1.5g/kg in one to three administrations 48.
A special consideration in these infants is the use of iron in HDFN. Infants with HDFN do not suffer from iron-deficiency anemia 49. Do not administer iron supplements without first confirming ferritin level 49, 50, 51. Inappropriate administration of iron in infants with HDFN can result in iron overload46 and adverse events such as cholestasis 56, portal hypertension, coagulopathy abnormal liver enzymes, free-radical damage 57, liver damage, or death. For infants with severe iron overload, chelation therapy with desferrioxamine is an option to prevent or reduce organ damage 51, 52, 53, 54. Folic acid can be safely given to neonates with HDFN 46. If hyporegenerative anemia is a concern, Erythropoietin can be used either alone or in combination with desferrioxamine if iron overload is a concern 55.
Erythropoietin has been in use since the 1990s as an adjunct treatment for late anemia and to increase a reduced reticulocyte count. In limited single-arm studies and case reports, erythropoietin has been shown to be safe 33, 38 and may reduce the need for transfusion in neonates with HDFN 46, 66, 68, 69, 70. In one 6-week study of 20 infants with HDFN due to anti-D, the “number of erythrocyte transfusions was significantly lower than that of the control group (1.8 versus 4.2). The reticulocyte counts and Hb levels rose earlier in the treatment group 13.” This may also be a treatment option for children whose parents object to the use of blood products for religious reasons 67.
Before discharge a follow up appointment should be scheduled with a pediatric hematologist or other provider. After hospital discharge, providers and parents should be aware that affected infants may develop significant anemia until 12 weeks of life, especially if they received IUTs during pregnancy (see “Delayed Onset Anemia“). The discharging physician should alert the family pediatrician or pediatric hematologist of the follow up care plan.
During the first week of life, bilirubin should be checked daily, especially considering that bilirubin due to alloimmunization tends to peak at days four to six. Hemoglobin should be checked at least one additional time in the week after birth 44. Afterwards, weekly hematocrit and reticulocyte counts should be assessed and simple transfusions initiated if hemoglobin levels fall below 7 gm/dL or if symptoms are present.
Bilirubin should continue to be checked at least one to two times a week until a steady decrease is certain.Current guidelines state that infants with hemolytic disease of the fetus and newborn are at medium or high risk for developing severe hyperbilirubinemia and its consequences “If phototherapy is used for infants with hemolytic diseases or is initiated early and discontinued before the infant is 3 to 4 days old, a follow-up bilirubin measurement within 24 hours after discharge is recommended. 45” Home phototherapy is not an option for infants with HDFN and readmission may be necessary. In the case of infants who are readmitted for hyperbilirubinemia, a repeat TSB after subsequent discharge is an option 45.
For additional information on infant testing, see necessary laboratory assessments for infants exposed to maternal alloantibodies.
Though cost is generally a prohibitive factor, options exist to prevent alloimmunization entirely in subsequent pregnancies. This includes:
To see additional information on alternatives to natural conception visit our Alternatives to Natural Conception page.
If a woman intends to become pregnant again, pregnancy monitoring and potential interventions can be pre-planned with a supportive provider. This may include IVIG and plasmapheresis beginning in the first trimester and assessment for eligibility for inclusion in new clinical trials such as that for nipocalimab. To see additional clinical trials relating to alloimmunization and HDFN, visit our Current Research and Clinical Trials page. For women with previously affected pregnancies requiring IUTs, referral to a specialist with extensive experience in IUTs, IVIG and plasmapheresis may be considered and pre-pregnancy consultation should be initiated.