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Rhesus disease explained

Babies inherit their blood type from their parents, but when the child’s blood type isn’t compatible with the mother’s, it can cause serious problems that endanger the pregnancy.

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Rhesus disease can endanger a woman's pregnancy

Babies inherit their blood type from their parents, but when the child’s blood type isn’t compatible with the mother’s, it can cause serious problems that endanger the pregnancy. The mother’s immune system could create antibodies that attack the baby’s red blood cells.

It’s only a concern when the mom is Rh (Rhesus) negative and the foetus is Rh positive, but what does that mean?

You probably know your blood type, which is expressed as a letter (A, B, AB or O) and + (positive) or – (negative). Positive means you have the Rhesus factor, which is an inherited protein found on red blood cells. Negative means you don’t have Rhesus factor and your blood type is A negative, B negative, AB negative or O negative.

So if the child’s mother is Rh negative and the father is Rh positive, the baby could be negative or positive. That’s why some pregnant women receive an injection derived from human plasma that contains Rh-positive proteins.

The injection temporarily tricks a Rh-negative mother's immune system into thinking there are already antibodies to the Rh-positive cells in the baby's blood. This means the mother's body does not produce antibodies to the Rh-positive factor in the baby's red blood cells. The risks from Rh incompatibility are especially severe with second pregnancies.

Until about 70 years ago, mothers who were Rh negative often lost babies after their first pregnancy because their immune systems created antibodies that crossed the placenta and attacked the red blood cells of their Rh-positive babies. This caused anaemia that led to heart failure.

Even today, half of untreated babies who are Rh negative die or experience brain damage, according to the Plasma Protein Therapeutics Association (PPTA).