I am 16 weeks pregnant, and I found out that my blood type is Rh. The father of my baby had to have a blood test to determine his blood type, which is O positive. I have heard about a shot that I will have to receive because the two blood types are not compatible. Is this true? What is the shot made of? Will it hurt my baby? Is my baby hurting right now because I have not yet received this shot? What causes my blood type to be this way? I never had my blood type determined until now, and I want to know if there are any other health problems I will have to face because of my blood type.

Jennifer

The "blood type" label actually describes two different characteristics of the blood -- your ABO group and your Rh group. Both characteristics are determined by the genes you get from your parents. Your ABO type may be A, B, AB or O, and your Rh type may be positive or negative. The two components are determined by two different sets of genes. For example, if you get an A gene from your mom and a B gene from your dad, your blood type will be AB. If both parents also give you a Rh negative gene, then you will be AB negative.

It sounds like you are Rh negative. This means you have two negative Rh genes -- one that you got from your mother and one from your father. The word "positive" in your boyfriend's blood type means he's Rh positive. The positive gene is dominant, which means your boyfriend could have two positive genes, or he could have one positive gene and one negative gene and still have Rh-positive blood.

Your baby will receive a Rh negative gene from you, because that's the only kind you carry. Your baby, however, could end up with either Rh negative blood (if it received a negative from you and one from the baby's father) or Rh positive blood (if it received a negative from you and a positive from him). If the baby is Rh negative, then there are no worries; its blood is compatible with yours. If the baby is Rh positive, however, then your body could produce antibodies that could potentially lead to breakdown of the baby's blood cells and anemia. Because we do not know the baby's blood type until after the baby is born, you will be given a shot called Rhogam; Rhogam blocks the production of these antibodies, preventing them from causing any harm to the baby.

Being Rh negative does not have any health consequences for you. Many of us do not know our blood types unless we have donated blood in the past -- or during pregnancy, when all women have their blood type determined in order to see if Rhogam will be necessary.