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1. Blood group (O, A, B, AB)

2. Rhesus system ² C, D and ED

antigens

When fetal red cells pass across to the

maternal circulation, as they do to a greater orlesser extend during pregnancy, sensitizationof the maternal immune system to these fetal'foreign' red blood cells may occur.

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ABO blood group iso-immunization mayoccur when the mother is blood group O and

the baby is blood group A or B. Anti-A andanti-B antibodies are present in the maternalcirculation naturally, and hence do not requireprior sensitization in order to be produced.

This means that ABO incompatibility mayoccur in a first pregnancy.

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In this situation, anti-A or anti-B antibodiespass to the fetal circulation, causing fetalhaemolysis and anaemia. ABO incompatibility

causes mild haemolytic disease of the baby, butmay sometimes explain unexpected jaundice inan otherwise healthy term infant.

The D antigen is associated most commonlywith severe haemolytic fetal disease. This canonly occur if the mother is D rhesus negativeand the baby is D rhesus positive.

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Rhesus disease does not affect a firstpregnancy. The mother must have exposure

to D rhesus-positive fetal cells in a previouspregnancy and then developed and immuneresponse that has lain dormant until afollowing pregnancy of a D rhesus-positive

baby.

IgG antibodies cross from the mother to thefetal circulation.

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Miscarriage

Termination of pregnancy

Antepartum haemorrhage

Invasive prenatal testing (chorion villus

sampling, amniocentesis and cordocentesis)

Delivery

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Rhesus-negative mother, rhesus-negativefather (homozygote)

Rhesus-negative mother, rhesus-positivefather (heterozygote)

Rhesus-negative mother, rhesus-positivefather (homozygote)

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ABO

Rhesus (C, D, E)

Kell

Duffy

c (know as 'little c')

S

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(Mildest)«

Normal delivery at term; mild jaundice

requiring phototherapy Preterm delivery of an anaemic fetus requiring

exchange transfusion

Delivery of fetus at 34 weeks following

fortnightly blood transfusion from 26 weeksgestation.

Stillbirth or neonatal death due to rhesus (earlier

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Blood may be given to the baby by a needleintroduced through the mother's abdomen.Blood is given either intravascularly (into theumbilical vein or heart) or intraperitoneally.

Blood transfused to the fetus must be:- concentrated (Hb normally 22-24g/dL)- cytomegalovirus negative- rhesus negative- irradiated (to reduce the risk of graft-versus-host disease)

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