The mother, exposed to the Rh-positive blood during delivery or during pregnancy, produces antibodies against her infant's blood.

Most women who become sensitized do so during childbirth, when their blood mixes with Rh-positive fetal blood.

Bleeding from an abruption can mix the Rh-positive blood with yours.

But the health of a baby with Rh-positive blood during a future pregnancy is more likely to be affected.

If your blood is Rh-negative, it will also be tested for antibodies to Rh-positive blood.

If you have antibodies, that means that you have been sensitized to Rh-positive blood.

At the first prenatal visit, your blood is tested to see if you have been previously sensitized to Rh-positive blood.

Some women do not become sensitized even though they are exposed to large amounts of Rh-positive blood.

The baby may have Rh-positive blood if the father has Rh-positive blood.

Rh-positive blood does have this marker.