The Rhesus factor (Rh factor) is a surface antigen of erythrocytes. The term "Rhesus" was coined since it was first discovered in Rhesus monkeys. The Rh blood group system consists of multiple antigens (over 50), but D, C, c, E, and e are the most common antigens identified. D antigen is mainly responsible for Rh disease due to its high immunogenicity. A person can be Rh-positive or Rh-negative based on the presence or absence of D antigen on the surface of red blood cells, respectively.
Rh-hemolytic disease, also known as Rh incompatibility, is a condition that occurs when a woman with Rhesus-negative blood type is exposed to Rhesus-positive blood cells, leading to the development of anti-D antibodies by a process called as isoimmunization. After this sensitization, these maternal alloantibodies (IgG immunoglobulins) may persist for life and move freely across the placenta to the fetal circulation during subsequent pregnancies, where they lead to the destruction of fetal erythrocytes after forming antigen-antibody complexes with their surface D antigen. This results in alloimmune hemolytic anemia in the fetus known as erythroblastosis fetalis. The severity of illness depends greatly on the number of immunoglobulins, the gestational age, and the enzymatic activity of the fetus.
If undiagnosed, the mortality rate is high, at 24% in neonates. Universal parental Rh screening and prophylaxis treatment with Rh immunoglobulin have significantly reduced neonatal mortality rates.
There are two main causes responsible for Rh Hemolytic disease. The first is the exposure of an Rh-negative pregnant mother to Rh-positive fetal erythrocytes due to fetomaternal hemorrhage during pregnancy secondary to normal delivery, spontaneous or induced abortion, ectopic pregnancy, placenta previa, lack of prenatal care, invasive obstetric procedures (cordocentesis, chorionic villous sampling, amniocentesis), external cephalic version, c-section or trauma.
After the sensitization of the mother due to the formation of anti-D IgG immunoglobulins, future pregnancies are at risk for the development of the hemolytic disease of the newborn (HDN) due to Rh incompatibility if the fetus is Rh-positive. These IgG antibodies can cross the placenta and cause hemolysis causing severe fetal anemia and hyperbilirubinemia, which can cause neurological damage or death. Secondly, a less common cause of Rh incompatibility is the transfusion of an Rh-negative female with Rh-positive blood, especially during an emergency.
The varying prevalence of Rhesus negative type individuals around the globe has caused a significant impact on the incidence of disease worldwide. 15% of Whites (North Americans and Europeans) are found to be Rh-negative, while only 4%-8% of Africans and 0.1%-0.3% of Asians have the Rhesus negative blood group. Despite a remarkable decline in reported cases of Rh-hemolytic disease due to proper prenatal screening and prophylaxis, 276 neonates per 100,000 live births per year are still being affected globally, especially in developing countries.
The southwest United States has a 1.5 times greater incidence rate than the national average, probably due to immigration factors. The risk of death and stillbirths are 24% and 11% respectively among these affected newborns, while 13% of affected neonates develop kernicterus with the highest reported mortality rates in the Eastern Europe/Central Asian region with 38 deaths per 100,000 live births. The presence of co-existing ABO incompatibility decreases the incidence of this hemolytic disease drastically because of the presence of anti-A/anti-B antibodies against the fetus in maternal serum.
The sensitization of the mother depends on multiple factors, including the volume of transplacental hemorrhage, the extent of the maternal immune response, and the concurrent presence of ABO incompatibility. It affects 17% of pregnant women with 1mL of Rh-positive cells and 70% after 250mL of rhesus positive cell exposure. When Rh-positive fetal RBCs leak into maternal circulation after breakage of the embryonic chorion, which normally separates fetal and maternal circulation, the immune system of Rh-negative women considers these cells as foreign and mounts a primary immune response by producing IgM antibodies initially.
Generally, no effects are seen in first pregnancies for Rh-D mediated disease as IgM is a large pentamer that can not cross the placental barrier. However, during the following pregnancies, subsequent exposure of as little as 0.03mL of Rh-positive cells can lead to the formation of anti-D IgG immunoglobulins, which cross the placenta freely and bind to fetal red blood cells containing D-surface antigen. These antibody-coated cells are recognized by the fetal reticuloendothelial system, and the destruction of these cells causes the release of large amounts of bilirubin in fetal circulation. During the antenatal period, maternal conjugation enzymes remove the excess of bilirubin, but after birth due to early insufficiency of glucuronyltransferase enzymatic activity, neonates present with jaundice or kernicterus and severe hemolytic anemia.
In Rh-hemolytic disease of the newborn, the following changes are seen in the peripheral blood smear:
Detailed history regarding maternal and paternal Rh blood grouping, prior blood transfusions, previous pregnancies especially with the history of Rh-hemolytic disease, trauma or invasive obstetric procedures, spontaneous or induced abortions, and administration of Rh IgG should be obtained carefully. Physical examination depends on the severity of the disease.
Neonates with mild Rh-hemolytic disease exhibit only mild jaundice during the first few days of postnatal life. They recover without any subsequent damage. Moderately affected infants may have anemia and jaundice both at the same time. Severely affected newborns develop kernicterus several days after delivery due to the deposition of unconjugated bilirubin in tissues of the central nervous system. Kernicterus is characterized by loss of early neurological reflexes e.g., Moro reflex, posturing reflex, bulging fontanelle, arching of head and heels back like a bow, floppy body, a high pitched cry, poor feeding, and generalized tonic-clonic seizures. Premature infants are more prone to develop neurological damage in Rh-incompatibility. Around 83% of neonates with kernicterus develop permanent neurological damage later in life.
Severe Rh-hemolytic disease can also cause a life-threatening condition in infants called erythroblastosis fetalis characterized by jaundice and severe hemolytic anemia. Hydrops fetalis is the most severe form of erythroblastosis fetalis, which develops in infants with extreme pallor having a hematocrit less than 5 and is associated with more than a 50% mortality rate. Newborns with this pathology have the following symptoms: generalized edema, pleural or pericardial effusions, high output cardiac failure, and extramedullary hematopoiesis.
The first step in evaluation is the determination of Rh blood type in every pregnant female, according to the recommendations of the United States Preventive Services Task Force (USPSTF).
If a woman is Rh-positive, there is no need for further testing. If a woman is Rh-negative, the second step is the determination of anti-D antibody presence in the maternal serum initially by a qualitative rosette test and later on by a quantitative Kleihauer-Betke test. This is a confirmatory test to quantify antibody titers, especially in large hemorrhage (>30ml blood) recommended by the American College of Obstetricians and Gynecologists (ACOG). A Coomb's test is used for confirmation if antibody titers are positive. Antibody titers level should be less than 1:16, a level greater than this requires further serial amniocentesis started as early as 16-20 weeks to determine fetal Rh status.
Fetal surveillance depends on Rh positivity of the fetus. It is usually done by serial pelvic ultrasounds, umbilical artery doppler, and middle cerebral artery (MCA) dopplers to monitor fetal growth if an Rh-positive mother is carrying an Rh-negative fetus. MCA doppler is primarily used to screen anemia in Rh-positive fetuses. It is usually performed every 1-2 weeks beginning at 24 weeks gestation with the use of peak systolic velocity (PSV) as the main parameter as it increases in anemic fetuses. A PSV level >1.5MoM needs further investigations.
Negative antibody testing further requires paternal Rh testing. If the father is Rh-negative, then no more testing is required. On the contrary, if the father is heterozygous Rh-positive, there is a 50% chance for the fetus to be Rh-negative or positive. So in such cases or where paternal Rh grouping is not possible, fetal Rh genotyping is required either by non-invasive methods or by invasive techniques. Non-invasive fetal RHD genotyping is done in the first 12 weeks of pregnancy by taking a maternal blood sample, and this procedure is found to be 97% accurate with specificity and sensitivity 93% and 100% respectively in determining Rh status. Amniocentesis and chorionic villus sampling are the preferred invasive procedures to analyze fetal DNA to devise a future management plan.
If a woman presents in the emergency department for delivery without any prior prenatal investigations, then blood samples are taken from the umbilical cord of the infant for blood grouping and Rh typing, hematocrit, and hemoglobin level measurement and serum bilirubin analysis. Direct Coombs test is also performed to confirm the diagnosis of antibody-induced hemolytic anemia, which is more commonly due to Rh-incompatibility than ABO incompatibility. Increased bilirubin, low hematocrit, and high reticulocyte count may indicate the need for early exchange transfusion.
Imaging studies include pelvic ultrasound mainly which can show signs of fetal ascites, soft-tissue edema, scalp edema, pleural and pericardial effusion, cardiomegaly, and hepatomegaly with portal hypertension in the case of a severely affected fetus.
Rh immunoglobulins (RhIVIG), introduced about five decades ago, have proven to be extremely effective as a main prophylactic treatment in Rh-incompatibility. After this invention in the year 1968, a significant decline in the incidence of Rh-hemolytic disease has been observed along with a two-thirds decline in the mortality rate in nationwide surveillance. As discussed earlier, it is given to all Rh-negative women only when alloimmunization has not occurred, carrying Rh-positive fetuses either prophylactically or after abortion or fetomaternal hemorrhage. It has the ability to coat fetal RBCs having surface D antigen, making antigen-antibody complexes that move across the placenta before activation of the maternal immune system. Having a short half-life of 3 months, it is given once during 28 to 32 weeks antenatally and then in the postpartum period within 72 hours after the birth of the baby in a standard dose of 300 mcg (1500IU) for every 30 mL of fetal whole blood exposed to the maternal circulation. However, the dose adjustments can be done according to the degree of hemorrhage by estimation of fetal RBCs in maternal circulation with the Kleihauer-Betke acid-elution test because hemoglobin F resists acid elution. In the case of abortion (<13weeks), a mini dose of 50mcg (250IU) should be given and a complete standard dose in case of a miscarriage.
Phototherapy can be used to treat jaundice. However, the use of a high dose of IVIG has significantly reduced the duration of phototherapy treatment.
Exchange transfusion is another effective therapy after phototherapy to treat neonatal hyperbilirubinemia, thus decreasing the chances of the infant developing kernicterus.
In-utero blood transfusion depends on anemic severity of the fetus, which can be estimated precisely antenatally by PSV of middle cerebral artery Doppler, which has a sensitivity and specificity in predicting any degree of anemia of 88.46% and 98.27% respectively. Post-natally, a hematocrit level of <30% is an indication for blood transfusion. These transfusions can be done by the intravascular route, preferably or by the intraperitoneal route as an alternate.
Rh-hemolytic disease presents clinically as jaundice, anemia, and serum indicates unconjugated hyperbilirubinemia. Bilirubin is conjugated to be excreted from the body by UDP-glucuronosyltransferase (UGT) 1A1. UGT1A1 enzyme deficiency or excessive production of bilirubin is responsible for this state. As such, the first step is to differentiate physiologic jaundice from other causes of pathologic jaundice. Physiologic jaundice, which presents on the second or third day of postnatal life has bilirubin levels less than 12mg/dl, 20% more incidence in premature infants, and usually subsides within the first week without any consequences. Jaundice within the first 24 hours after birth or with largely elevated bilirubin levels is pathological, and it needs detailed investigations.
The most common cause of pathological hyperbilirubinemia is breast milk induced jaundice due to probable caloric deficiency in these breastfed infants and the influence of breast milk on UDP-glucuronyltransferase enzyme system.
Other important causes for this physiopathology are ABO incompatibility, hereditary spherocytosis, hereditary enzyme deficiencies, fetomaternal hemorrhage, twin transfusion syndrome, thalassemia, especially alpha thalassemia, and thrombotic microangiopathies. Investigations to differentiate these conditions from Rh-incompatibility are complete blood count with differential, peripheral blood smear, conjugated and unconjugated bilirubin levels, liver function tests (serum alanine aminotransferase, aspartate aminotransferase, gamma-glutamyltransferase, alkaline phosphatase, and albumin level), serum blood markers to differentiate intravascular hemolysis causes from extravascular causes (e.g., lactate dehydrogenase level, hemosiderin level in blood and urine, haptoglobin level), reticulocyte count, RDW (red cell distribution width), and direct and indirect Coomb's test.
The introduction of Rho (D) immune globulin has significantly decreased the incidence rate of Rh-hemolytic disease. According to a study, the incidence rate of this hemolytic disease declined from 40.5% to 14.3% per 10,000 births during the first decade of the IVIG introduction.
The availability of advanced antenatal screening, modern diagnostic modalities, and state-of-the-art intensive healthcare facilities, especially in developed countries like the United States, have reduced the prevalence of Rh-hemolytic disease, and it's associated mortality rate to a minimal level. However, as mentioned earlier, rates are still relatively higher in developing countries involving around 276 infants and neonates/100,000 live births. The mortality rate in infants with hydropic features is relatively greater than in a non-hydropic newborn.
Association of preventable Rh-disease with high morbidity and mortality makes it crucial for health care providers to educate patients regarding the importance of timely intrauterine screening and immunoprophylaxis in the third trimester to avoid this. Improvements in access to health care have made it easier for health professionals to diagnose the Rh status of parents earlier, and this has greatly changed the overall outcome.
A strong clinician-patient relationship is essential to enhance healthcare outcomes. Collaboration among interprofessional team members which includes an obstetrician, a primary clinician, and nurses mainly. The preventable nature of this disease makes it necessary for professionals to precisely evaluate and screen both mother and father during the first trimester and carefully monitor antibody titers of Rh-negative females. These antibody levels should be <1:16, and if it exceeds this, invasive testing is done to manage accordingly. Critical surveillance of the fetus with MCA doppler gives an accurate idea of fetal anemia, indicating whether there is a need for intrauterine transfusion or not.
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