Rhesus incompatibility

• The most relevant antigen within the rhesus blood group system is the rhesus-D antigen.
• Women that are rhesus-D positive do not need any additional treatment during pregnancy.
• Overview:

  • rhesus negative woman's child could be rhesus positive
  • Likely at some point in the pregnancy that blood from the baby will enter the mothers blood stream
  • The mothers immune system will produce antibodies to the babies rhesus-D antigen = mother sensitised to rhesus-D antigens
  • Sensitisation process does not cause problems during first pregnancy
  • During subsequent pregnancies the mothers anti-rhesus-D antibodies can cross the placenta into the foetus
  • Antibodies attach themselves to the red blood cells and cause the immune system to attack them
  • Haemolytic disease of the newborn
• Management:

  • Prevention is mainstay of management
  • Anti-D injections given routinely at 28 weeks and at birth (if baby rhesus-positive)
  • Anti-D works by attaching itself to the rhesus-D antigens on the foetal red blood cells in the mothers circulation, causing them to be destroyed
  • Anti-D also given at any time where sensitisation may occur e.g. APH, amniocentesis (within 72 hours)
  • Kleihauer test used after any sensitising event past 20 weeks to assess whether further doses of anti-D is required
• Kleihauer test:

  • Checks how much foetal blood has passed into mothers blood during a sensitisation event
  • Used to check whether further doses of anti-D are required
  • Add acid to sample of mothers blood
  • Foetal haemoglobin is naturally more resistant to acid so they are protected against the acidosis that occurs around childbirth
  • Foetal haemoglobin persists in response to the acid, the mothers haemoglobin is destroyed
  • The number of cells left still containing haemoglobin (remaining foetal cells) can then be calculated