HAEMOLYTIC DISEASE OF THE NEW BORN (HDN)

Haemolytic disease of the newborn (HDN) occurs when the mother has anti-red-cell IgG antibodies in her plasma that cross the placenta and bind to fetal red cells bearing the corresponding antigen. The three most common red cell alloantibodies which cause significant HDN are anti D, anti c and anti Kell (anti K).

Fetal red cells binding sufficient maternally derived antibody are destroyed in the fetal reticuloendothelial system, producing extravascular haemolysis and a variable degree of fetal anaemia. In severe cases the fetus may die in utero of heart failure (hydrops fetalis). If the fetus survives birth, the neonate rapidly develops jaundice and is at risk of neurological damage due to the high Bilirubin level.

Development of red cell antibodies in the mother may occur either as a result of:

Previous pregnancies (because fetal blood displaying paternal red cell antigens frequently enters the mothers circulation during pregnancy). As a result of a previous blood transfusion.

The three most common red cell alloantibodies which cause significant HDN:

Antibody to the Rh antigen: The most common is anti D.This develops in RhD negative women who have carried a RhD positive fetus. It rarely affects the first pregnancy although it can sensitize the mother so that subsequent pregnancies with RhD positive babies boost antibody production progressively, putting later pregnancies at increasing risk.

Smaller family sizes and the introduction of prophylaxis with RhD immunoglobulin have reduced the incidence and severity of this condition. The fetus is only at risk if its red blood cells express the antigens against which the antibody is directed (e.g. if a RhD negative woman with anti D is carrying a RhD positive fetus, there is a risk that the fetus will be affected, but if the fetus is RhD negative the baby will not be at risk of HDN).The next most common causes of severe HDN are the rhesus antibody anti c.

Treatment Exchange transfusion

2- Kell antibody (anti K).

In HDN due to anti K, the antibody also causes reduced fetal red cell production. This is due to anti K binding to red cell progenitor cells; in such cases the anaemia is often very severe while jaundice may be minimal. Although it is not usually severe.

3-Antibodies of the ABO blood group system

in a group O mother with naturally occurring anti-A and anti-B of the IgG subclass which can cross the placenta. HDN due to ABO incompatibility occurs when a group O mother with IgG anti-A or IgG anti-B is carrying a fetus of blood group A or blood group B respectively. The most common presentation of ABO HDN is jaundice (un-conjugated hyperbilirubinaemia).

The direct antiglobulin test is usually (but not always) positive. Severe anaemia in HDN due to maternal anti-A or anti-B is uncommon in Caucasians in the UK, but is commoner in some other ethnic groups, especially among women of African or Caribbean origin.

ABO haemolytic disease of the new bornChild rarely requires treatment by exchange transfusionBlood film shows auto agglutination and shperocytosis

Prevention

Anti-D immunoglobulin (Routine antenatal anti-D prophylaxis) is prepared from plasma of donors who have high levels of plasma anti-D due to exposure to RhD positive cells following pregnancy or intentional immunization. Anti-D products contain specified levels of anti D and are available for intramuscular or intravenous administration. Prevention of HDN due to anti RhDAnti RhD immunoglobulin (anti D)

Anti D is administered to RhD negative women who may have been exposed to RhD positive fetal red cells that have entered the maternal circulation. The anti D destroys the RhD positive red cells and prevents active immunization, thus preventing the production of RhD antibodies.

Clinical features

Severe disease : intrauterine deathModerate disease : the baby born with severe anaemia and jaundiseMild disease : mild anaemia

Treatment

Exchange transfusionManagement of pregnant women and prevention: The ABO and Rh blood groups of all pregnant mother determined early in pregnancy The severity of the haemolytic disease can be assessed by estimation the bile pigment derivatives in the aminotic fluidSuitable fresh blood should be available at the time of induction for exchange transfusion

A birth the babies of Rh-negative who do not have antibodies must have their Cord blood grouped for ABO and Rh : - If the baby Rh-negative ( no need for treatment( - If the baby Rh-positive (prophylactic anti-D should be administered5. Prevention of Rh immunization : by giving (anti-D) to an Rh (D) negative mother giving birth Rh-positive baby . The routine dose is 500 i.u of anti-D giving intramuscular within 72 hours of delivery.

Laboratory findings at birth

Cord blood * variable anaemia (haemoglobin

Potentially sensitizing events during pregnancyPSEs are events that may cause feto-maternal bleeding and can cause the mother to develop anti D.If the pregnancy has reached 20 weeks or longer, patients with any of these events should receive anti D followed by a test that determines the volume of fetal red cells in the maternal circulation.If there is repeated antepartum haemorrhage (APH) during the pregnancy, further doses of anti D should be given at six-weekly intervals.

The identification of cells containing haemoglobin F depends on the fact that they resist acid elution to a greater extent than do normal cells, they appear as isolated, darkly stained cells among a background of palely staining ghost cells. The occasional cells that stain to an intermediate degree are less easy to evaluate; some may be reticulocytes because these also resist acid elution to some extent.