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Rh Incompatibility
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Description
In more than 98% of cases, red blood cell incompatibility between a mother
and the baby she is carrying involves the Rhesus
or Rh D antigen so the disease is known as
Rhesus disease , Rh disease
or Rh Incompatibility .
If a Rh-negative woman conceives a child with
a Rh-positive partner, the potential exists
for the child to inherit its father's Rh-positive blood type.
During the , blood
cells from the unborn child can escape into the mother's bloodstream.
These cells are recognised as foreign if they are Rh-incompatible (Rh
positive compared to mother's Rh-negative) and a natural rejection process
will ensue with the formation of antibodies. The process is known as red
cell alloimmunisation and typically occurs after the
of a baby at the end of pregnancy, but other pregnancy-related events
such as , , ,
or can result in antibody formation. Although the pregnancy
in which the alloimmunisation first occurs results in an unaffected child,
future children are at substantial risk, as in subsequent pregnancies,
newly formed antibodies in the pregnant woman can cross to her unborn
child and attach to its red blood cells producing anaemia and in the worst
case scenario, foetal death.
Data from the U.S. Centres for Disease Control indicate that the incidence
of haemolytic disease of the newborn secondary to Rhesus disease is approximately
1 per 1000 live born infants.
Prevention & Treatment
Medication is available to prevent Rhesus disease. Rh0(D)
immune globulin should be administered to the Rh-negative woman
with a Rh-positive partner any time there is a chance foetal cells may
enter the pregnant woman's circulation. Rhesus immune globulin should
be administered routinely at 28 weeks of pregnancy and after the delivery
of an Rh-positive infant. If given correctly, this medication is more
than 99% effective in the prevention of Rhesus disease. Rhesus immune
globulin is only effective in preventing Rhesus disease; it is not effective
in preventing worsening disease once alloimmunisation has occurred.
In 12% of first affected pregnancies, the infant may require intrauterine
transfusions. In this procedure, a needle is directed under ultrasound
guidance into the umbilical cord and blood is infused directly into the
foetus to correct its anaemia. The procedure is usually repeated at 2
to 3 week intervals for the remainder of the pregnancy until approximately
35 weeks of the pregnancy. The survival rate after intrauterine transfusion
is approximately 85%.
The information in this page is presented in summarised form and has been taken
from the following source(s):
1. The University of North Carolina, Department of Obstetrics
& Gynecology, Women's Wellness & Specialty Services:
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Introduction
