Erythroblastosis fetalis of neonates, also erythroblastosis neonatorum or hemolytic anemia of the newborn is caused by the transmission of antibodies to the red blood cell of the fetus through the placenta in intrauterine life. It is caused by incompatibility of the maternal blood group and the fetal blood group, mostly the Rhesus D antigens of the blood. Erythroblastosis fetalis only occurs when the mother is Rh-.
Erythroblastosis fetalis occurs as a result of the sensitization of the mothers Rh- blood due to exposure to Rh-D antigens either by blood transfusion or tearing of the placenta during child birth in which case the blood of the Rh+ fetus mixes with that of the Rh negative mother. As a result of the production of anti-bodies, subsequent Rh+ babies will be subjected to erythroblastosis fetalis because the body of the synthesized mother will attack the baby’s red blood cell due to the presence of Rh-D antigens.
The first Rh+ child of a Rh- woman is free of this disease if the mother is yet to be sensitized by any other means. If the subsequent child is Rh-, the child is also free from this disease. Other fetomaternal incompatibilities that may lead to erythroblastosis fetalis are the Kell, kidd, MNSs, Diego, Cc, Ee, Xg antigen systems, among others. ABO blood group incompatibility doesn’t cause erythroblastosis fetalis.
The first step of diagnosis is prenatal maternal blood typing and screening. The blood group and Rhesus factor of the woman is determined. She is also screened for anti-RhD and any other anti-bodies that may have developed due to exposure of any of the antigens that may lead to erythroblastosis fetalis. If the mother is found to be Rh+, normal pregnancy procedures are carried on. If the mother is Rh- and has any of the anti-bodies caused by erythroblastosis fetalis causing antigens, then the next step will be to test the blood of the father, if the paternity of the child is certain.
The blood of the father is screened and tested to determine his Rh factor and to determine if he has any of the antigens that may lead to erythroblastosis fetalis. If the father has neither of the antigens, then the child will be 100 percent free of these antigens and will be free of erythroblastosis fetalis. However, if he is Rh+ or has the anti-body causing antigen, the next step will be to measure the maternal anti-Rh antibodies titers.
If the titer value is positive but not up to the laboratory specific critical value, then they she comes back to have them measured every 2 to 4 weeks after the 20th week. If the critical value is exceeded, middle cerebral artery (MCA) blood flow is measured to detect high output heart failure indicating high risk of anemia. Elevated MCA blood flow during gestational age would lead to consideration of umbilical blood sampling and intra uterine blood transfusion. if the father is heterogynous for Rh-D antigen or any of the anti-body causing antigen, the Rh factor of the child is uncertain so the MCA is still carried out and elevated blood flow means high risk of anemia as well.
If the fetus is at risk of anemia, fetal blood transfusions will be carried out by a specialized in a well-equipped hospital every 1 to 2 weeks. This is done until about 32-35 weeks when the child would be delivered. Delivery may be required earlier if the MCA blood flow increases severely.
When the Rh- woman is pregnant with her first Rh+ baby and she has not been previously sensitized, she is given Rh-D immune globulin at:
- 28th week of pregnancy
- 72 hours of terminating the pregnancy either by delivery or abortion or treatment of ectopic pregnancy.
- After any occurrence of vaginal bleeding
- After amniocentesis or chorionic villus sampling
All these processes help prevent her from being sensitized against the Rh-D antigen. The Rh-D immune globulin consists of anti Rh-antibodies that neutralize the fetal Rh positive red blood cells in the mother after delivery.
Sensitization can occur earlier during the pregnancy so Rh-D immune globulin is also given at about 28 weeks into the pregnancy. A 2nd dose is also recommended if termination of the pregnancy has not occurred by the 40th week. It should also be given after any occurrence of vaginal bleeding and After amniocentesis or chorionic villus sampling