Rhesus disease (Rh incompatibility, Rh factor disease, Haemolytic Disease of the Newborn)

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What is Rhesus disease?

Rhesus disease (or Rh incompatibility) is a condition that results when a female of Rh-negative blood is exposed to Rh-positive blood cells and subsequently her body creates Rh antibodies to remove what it sees as an invading organism.

In the case of a pregnancy, if blood is shared amongst fetus and mother, the mothers antibodies will attach and attack the foetal red blood cells, leading to anaemia in the foetus. This is known as Haemolytic Disease of the Newborn.

The Rh Factor is a blood cell based surface antigen that was named in recognition of the monkeys in which it was first discovered.

Who gets Rhesus disease?

Figures tend to indicate that 15% of the population on average are considered Rh negative, meaning that 85% of the population are considered Rh positive.

Approxiamately 1 in 1000 births are considered succeptible to Rhesus disease.

Predisposing Factors

There are two ways Rhesus disease can occur. The first involves a Rh-negative mother being exposed to a Rh-positive foetus during the period of her preganancy.

If an Rh negative woman has a baby that is Rh positive, then it is possible for some of the baby's blood to enter into her system. This can happen under several circumstances:

During the birth,
Naturally (between 28 weeks and delivery),
During an amniocentesis,
At an abortion,
When a miscarriage occurs.

The condition can also occur during the course of a women receiving a Rh-positive blood transfusion.

The passing of Rh-positive foetal red cells into the maternal circulation sensitises the mother to form antibodies to the Rh antigen. Sensitisation does not pose a problem, however, if anti-Rh crosses the placenta to the foetus during the next pregnancy with an Rh-positive foetus, it will coat the foetal red cells with antibody and result in reticuloendothelial system destruction of the cells, causing anaemia and jaundice.