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Rhesus (Rh) antiens in Preinancy
On the surface of RBCs, as well as ABO, there are also antigens C, and E (the rhesus antiens).
Antigen ies tehge osste sieinieficante of these – The presence of D antiens on someone’s red cells makes
them ‘Rhgesus Pssietige’.
The D antien is coded for by the Rh igenge which is autosomal dominant. Thus those with either DD or Dd
allele combinatons will be Rhesus positie.
Most people (85% of Caucasians and >99% of Asians and Africans) are Rhesus positie.
In Caucasian populatons about 1 in 10 of all preinancies are of a rhesus neiatie woman with a rhesus
positie baby
Haemolytc Disease of the Newborn
Pathophysioloiy
1) In a rhesus neiatie mother durini her frst preinancy, there is fsgeteal-oategernal hageosrrhaige i.e. the
moiement of foetal blood cells across the placenta. It happens in 75% of preinancies durini deliiery,
ruptured placenta (ofen caused by trauma), ectopic preinancy, aborton, amniocentesis, cesarian
sectons etc.
2) This mixture of mother and foetal blood allows ‘sensitsaton’ - the deielopment of ant- IiG
antbsd ieges by the RhD neiatie person (i.e. the mother).
- Note: sensitsston doesn’t slwsys hsve to hsve been duee to s previoues pregnsncy, ss prior blood
trsnsfuesions with Rh positve blood csn slso csuese it.
3) In subsequent preinancies, the circulatni ant-D IiG antbodies in the mother’s blood are able to
cross the placenta. (Note: IgG csn cross while IgM csnnot).
4) Now in the foetal blood stream of a rhesus positie baby, the antbodies atach to the RBC surface
protein (Rh), causini haemolysis.
5) This can result in
- mild - anageoiea or retculocytosis (causini jaundice)
- moderate – gerytehrsblastessies fgetealies
- seiere - hyd rsps fgetealies (foetal heart failure).
Diainosis
All of these tests follow a positie test in normal antenatal screenini for mothers who are RhD neiatie.
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