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The Rhesus Factor It seems almost impossible to believe that a mother's blood could
threaten her baby's life, however between 1946 and 1948 one in every
200 women in England were affected by this blood type
incompatibility. Twenty percent of their babies died shortly after
birth, with the remaining women suffering miscarriages during
subsequent pregnancies.
Causes
Blood is divided into ABO groups, which are determined by the
presence or absence of certain protein molecules on the outer shell
of the red cells. Which proteins are present, depends on genes
inherited from the parents - An A, B, AB or O blood group will be
inherited just as is hair or eye colour. Blood types are also
inherited, with all blood being either Rh-positive (containing
factor D - the Rh factor) or Rh-negative. Rhesus (Rh)
incompatibility is an incompatibility between the Rhesus blood
groups of the mother and the developing baby, as different blood
groups don't mix. Therefore, Rhesus incompatibility would only occur
if the mother has Rh-negative blood and the baby has Rh-positive
blood (through having inherited Rh-positive genes from the father).
When Rh-positive blood enters the circulation of an Rh-negative
person, the body reacts in a similar way as it would when fighting
off infection. Once the persons immune system detects an 'alien'
D-factor present in Rh-positive blood, specific anti-D antibodies
are formed to eliminate the 'alien'. This poses a problem during
pregnancy as an Rh-negative mother's body would react to the baby's
Rh-positive blood in the same manner as it would to foreign
material, thus producing antibodies to combat it. Since this
normally occurs as a delayed reaction after the baby is born, there
is a very good chance that the first baby will go unharmed. However,
the mother will continue to produce these antibodies after delivery
and, in any subsequent pregnancy where the baby has, Rh-positive
blood, they will begin to destroy the baby's red blood cells.
How common is rhesus incompatibility and what are the risks?
Approximately 85 per cent of the population are Rh-positive, meaning
that a Rh-negative woman having a child has an 85 per cent chance of
having the child by a Rh-positive man.
Only Rh-negative mothers carrying Rh-positive babies are at risk.
In the cases when it occurs, the baby is at risk of developing
haemolytic anaemia and neonatal jaundice at birth or, in extreme
cases, of being stillborn.
Risks are increased with each successive Rhesus incompatibility
pregnancy.
What should be done to prevent rhesus disease?
At the start of a pregnancy, each woman is given a blood test to
determine (among other things) whether you are Rhesus positive or
negative. If you are Rhesus negative, then your partner's blood will
also be tested and, if the results show that he is Rh-positive,
meaning that there is a chance that the baby will be Rh-positive,
you may be injected with Anti-D immunoglobulin during the pregnancy
or after the birth of the baby. Being your first pregnancy, you will
also have regular blood tests to ensure that yours is not a rare
case where antibodies develop before the baby is born. In subsequent
pregnancies, these tests are carried out to determine whether the
treatment given after your previous pregnancy was actually
effective.
In the case of modern treatment not having been available during
your first pregnancy, the blood test results will show a
concentration of antibodies in your blood. The effect they are
having on your developing baby can be detected through amniocentesis
or by taking samples of your baby's blood.
Treatment
The serum developed as a protective vaccination has almost
eliminated the dangers of Rhesus incompatibility. This serum is
given by injection to the mother soon after delivery or miscarriage,
haemorrhage or abortion. This acts by destroying any of the baby's
blood cells that may have entered the mother's bloodstream, before
her body had a chance to develop antibodies.
If it is found that the mother has already started to produce
antibodies, which are adversely affecting the unborn baby, she will
be hospitalised, and provided the baby is sufficiently mature,
labour will be induced. A baby who is still too immature to be born
may be given a blood transfusion while still in the uterus.
Following the delivery, the baby will most likely be jaundiced, and
depending on the severity may require an exchange blood transfusion.
Those that are not as severely affected can be carefully monitored.
The biggest problem for these babies is the fact that the red blood
cells continue to breakdown even after birth, as well as the
simultaneous danger of a build-up of bilirubin.
- Bilirubin:
During pregnancy, this waste product passes into the amniotic fluid
and then through the placenta to the mother's circulation from which
it is excreted from the body as the chief component of bile. After
birth the baby has to dispose of the bilirubin himself. Because
Rhesus babies often have immature livers which are also swollen from
exertion while trying to compensate for lost red blood cells, they
cannot do this. The bilirubin then builds up and is deposited in
tissues. Excessive levels of bilirubin stain the fatty tissues in
the skin yellow; this condition is called jaundice. If bilirubin
levels continue to rise, the baby will sustain permanent damage to
certain areas of the brain - the few babies that survive are usually
permanently brain damaged and deaf.
Thanks to the improved development of specialised units in most
hospitals, the future has a far brighter outlook for babies who have
Rhesus incompatibility.
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