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Explainer: What Is Rh Negative?

A treatment made from donated plasma helps Rh-negative moms have healthy babies.

For many moms, your plasma donation is the gift of life

Babies inherit their blood type from their parents, but when the child’s blood type isn’t compatible with the mother’s type, 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 negative and the fetus 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 yes, you do 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 istemporary, tricking the Rh-negative mother's immune system intothinking there are already antibodies to the Rh-positive cells in thebaby's blood. So the mother's body refrains from producing antibodies tothe Rh-positive factor in the baby's red blood cells,” said Dr. Alan Lindemann, an obstetrician and maternal mortality expert in Elgin, North Dakota, who has delivered more than 6,000 babies.

The risks from Rh incompatibility are especially severe with second pregnancies, said Dr. Kim Langdon, an obstetrician/gynecologist in Ohio.

“The problem does not arise in the first pregnancy, because the baby’s red blood cells that reach the mother’s circulation only cause a mild immune response in the mother – but in subsequent pregnancies the immune response can be massive,” she said.

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

Half of untreated babies who are Rh negative die or experience brain damage, according to the Plasma Protein Therapeutics Association (PPTA). Read about one mom who received the treatment on the association’s website.

This treatment wouldn’t be possible without plasma donors. Are you interested in becoming a plasma donor? Here’s a two-minute video explanation.