Haemolytic Disease of the Newborn and Foetus Flashcards
What is Haemolytic Disease of the Newborn and Foetus
A condition in which the life span of foetal red cells is reduced by the action of specific antibodies derived from the mother by placental transfer.
What led to a dramatic decrease in HDN cases after the 1970s
- Routine antenatal care including:
- screening of all expectant mothers to find those whose pregnancy may be at risk of HDN
- giving preventative tx accordingly
The disease involves (3)
- Maternal alloimmunisation -> produces antibody
- Transplacental passage of IgG antibody to the foetus
- Sensitisation and destruction of foetal cells
What type of immune system do newborns have
Primitive immune system
What keeps the foetus alive while they have their primitive immune system
The transport of the mothers antibodies across the placenta and into the fetal circulation. This occurs as their immune system matures.
What is a major cause of HDN
An incompatibility of the Rh blood group between the mother and foetus
Which pregnancies are at risk of HDN
Ones in which a Rd D- mother becomes preggers with a Rh D+ foetus (child inherited D+ antigen from father)
What is the Rh D- mother’s immune response to a Rh D+ foetus
The mothers immune response to the fetal D antigens is to form anti D antibodies against it
What type of antibodies are tha anti D antibodies and what does this mean
IgG antibodies. These type of antibodies can cross the placenta and be delivered to the fetal circulation.
Why is ABO incompatibility less severe than Rh incompatibility
Fetal rbcs express less of the ABO blood group antigens compared with adult levels
When may some foetal cells pass into the maternal blood system (2)
- At delivery
- Occasionally during pregnancy
Initially, what type of antibody is the maternal anti D antibody and can it cross the placenta
Initially, the anti D antibody is of the IgM type, this cannot cross the placenta
What happens in subsequent pregnancies after the formation of the IgM anti D antibodies
A repeat pregnancy with a Rh D+ child stimulates the rapid production of type IgG anti D antibodies which can cross the placenta into the foetal circulation
Once in foetal circulation what does the anti D antibody do
Attach to the Rh D antigens found on the foetal rbcs. This marks them to be destroyed.
What determines the nature of HBN to be mild, moderate or severe
The rate of haemolysis
What occurs in mild cases
- The small increase in red cell haemolysis is tolerated by the foetus
Symptoms (2) and tx of newborns with mild cases of HDN
- Mild anaemia
- Jaundice
Both of these may resolve w/o tx
What happens when there is an increased rate of haemolysis
- Bilirubin may remain low during pregnancy as placenta can remove bilirubin from the foetal circulation
- Post delivery the neonate’s immature liver is unable to metabolise the increased bilirubin accumulated in their blood
- Within 24 hrs bilirubin may rise and enter the brain, causing kernicterus
What is kernicterus and its prognosis
Kernicterus is a potentially fatal condition that leaves permanent neurological damage in the babies that survive.
Complications of HDN (6)
- Anaemia -> in foetus & neonate
- Jaundice -> elevated bilirubin
- Kernicterus -> seen in jaundice infants where bilirubin crosses into the brain and attaches and damages the brain tissue
- Hydropic -> bloated w fluid
- Hydrops foetalis -> watery foetus suffering from oedema bloated w fluid
- Erythroblastosis foetalis -> large no.s of nucleated rbcs in foetal peripheral blood
Testing of the mother (4 methods)
- Previous history -> of transfusions, pregnancies, infants affected by HDN
- ABO and Rh testing -> all Rh D- mothers must be identified
- Antibody screen -> should be performed using the IAT to detect IgG antibodies in the mother
- Antibody identification -> if antibody screen is positive, need to determine the identity of the antibody and its clinical significance
How many times must antenatal mothers be blood grouped
At least twice
What is performed to determine if a Rh+ mother has been sensitised to the Rh D antigen
An antibody screen is performed on her plasma
What is given to unsensitised mothers to reduce the risk of future sensitisation
Anti-D Ig
What does Anti D Ig do
Mops up any foetal rbcs that may have leaked into the mother’s circulation
When do Rh- mothers receive anti D Ig (2)
- At about 28 wks gestation, which is about when the foetal rbcs start expressing the D antigen
- A few wks before labour begins (Risk of feto-maternal hemorrhage is high)
When is the final dose of anti D Ig given
After the baby has been delivered if the baby is Rh +
How is the father tested
By doing a Rhesus genotype, which predicts the chances of having a Rh + baby
What are the chances of a Rh+ baby with a father who is homozygous DD
100% chance of foetus being Rh+
What are the chances of a Rh+ baby with a father who is heterozygous Dd
50% chance of foetus being Rh+
How can the level of haemolysis in the foetus be measured
The level of bilirubin in the amnion can be measured and is indicative of the level of haemolysis in the foetus
What other ways is the foetus tested (4)
- Foetal blood sampling for blood group
- Direct Coombs test
- Hb (anaemia)
- Bilirubin (jaundice)
What is the Doppler ultrasound used to test for in the foetus
Non invasive technique for measuring oedema and anaemia in the foetus
How is the neonate (newborn) tested
- Cord blood taken (representative of neonatal sample)
- ABO and Rh of infant
- Direct Coombs test -> see if maternal antibody has attached to infant’s cells in utero
- Hb level to assess anaemia
- Bilirubin level to assess jaundice
Management & tx of foetus with suspected HDN
- Intrauterine blood transfusions
-
Early delivery solution to Hydropic baby -> prematurity has risks
3.Phototherapy -> aids w excretion of bilirubin - Top up blood transfusions post delivery
- Immediate exchange transfusion post delivery -> alleviate the hyperbilirubinaemia, correct anaemia
