Rhesus (Rh) factor is an inherited protein on your red blood cells. If the protein if present on your red blood cells, your blood is Rh positive. If it's not present, you're Rh negative. A simple blood test can determine if a person is Rh negative or positive.
Rh negative blood is rare but several myths, phenomenons and oddities surround those with Rh negative blood.
Rh positive genes are more dominant than Rh negative ones. So a woman with Rh negative blood who conceives a child with a Rh positive man will likely have an Rh positive child.
And that can be problematic for the health of children.
During pregnancy and/or delivery, a mother's blood may come in contact with her baby's. And if an Rh negative mother's blood mixes with Rh positive blood from an infant, the mother's blood could develop antibodies to the Rh positive blood.
That's generally not a problem during a first pregnancy, but can pose health risks to an unborn child during subsequent pregnancies if future children are also Rh positive.
The antibodies in a mother's blood could cross the placenta and fight a fetus' red blood cells causing life-threatening anemia and risking the baby's life.
Injections of Rh immune globulin can help combat this.
About 15 percent of caucasians Rh negative while 5 to 10 percent of African Americans don't have the protein on the red blood cells. 1 to 2 percent of Asians are negative for the protein.
Those with ancestral roots in Basque provinces in Spain and France have the highest incidence of Rh negative blood than others around the world. Rh negative blood has been found to be significantly higher in Basques than those in neighboring European countries as well as other regions in Spain and France.
27 percent of Basques have type O Rh negative blood.
A higher percentage of Rh negative people claim to have been abducted by aliens than Rh positive people.