If a fetus receives one Rh+ gene from their father an one Rh- gene from their mother then that fetus will be Rh+.  Within the womb the fetus actually has their own separate blood supply from the mother that is carrying it so the mother will not immediately develop Rh+ antibodies unless there is some sort of internal trama to the fetus while in utero.  However, when the child is born there is a lot of blood exchange between the mother and the fetus and inevitably the mother will be exposed to the fetus’s Rh+ blood, whereby she develops an antibody to that factor D antigen.  The baby that has already been born will not be affected to by this fact however, if the mother has another infant that is born Rh+ there could be dire consequences.

If a mother with the Rh+ antibody has a fetus that is Rh+, the fetus will develop hemolytic disease of the newborn.  This disease is caused by the fact that the mother’s anti-Rh factor D antibodies cross the placenta and enter the fetus’s body.  Once inside the antibodies will attach to and destroy most of the fetus’s red blood cells, robbing their cells of the oxygen that blood carries.  Without serious medical intervention, the fetus will not survive at this point.  So what can be done about this rather common problem?

Today, mother’s that are O- are commonly given a shot called Rhogam which prevents the mother’s blood from coming into contact with the fetus’s Rh factor D antigens.  Without coming into contact with those antigens the mother will never develop the anti-Rh antibodies that can be so deadly to followup pregnancies.  This solution is simple and effective but it also makes yet another good case for good physician lead prenatal care.

Although Rh factor D is what determines the commonly referred to + or – blood type there are a lot of other blood antigens present in the body.  The reason that doctors don’t regularly refer to these other blood antigens is that they rarely cause problems with transfusions and therefore they are not commonly tested for in blood typing.  There are two situations where these other blood antigens can come up: pregnancy and repeated transfusions.  With repeated transfusions the body may have already had exposure to a commonly untested blood antigen and it will have created a corresponding antibody for that antigen, which will react upon the second transfusion.  Likely these transfusion reactions are mild in nature but occasionally can be life threatening.  The other place that these rare blood antigens become a problem is during pregnancy, which is talked about in this article.

Our bodies usually make antibodies only when we have been exposed to an antigen.  With almost all other antibodies found in the body we have to have an initial contact with the antigen before our body creates the corresponding antibody.  However, with ABO blood types we are born with antibodies for antigens that we do not have in our body.  So someone with type A blood would have anti-B antibodies which would react if they were given type B blood and vice versa for someone with type B blood.  The reason for the early presence of these antibodies in our blood is not fully understood and theories for their presence abound.  One of the more credible theories is that we are exposed to the antigens in our environment without us knowing it at some very early part of our upbringing.

Since your blood type is inherited, you get one gene for your father’s blood type and one gene for your mother’s blood type to combine and form your blood type.  So someone with type A blood would have to have a mother or a father that had type A blood also.  If you are type A then you would have you would be genetically coded for either two type A genes, or a type A and a type O gene.  The same setup works with type B.  Someone that is blood type AB would have both a type A gene and a type B gene.  People with blood type O would have two genes that don’t code for either type A or type B antigens.  What that means for people with type O blood is that they carry both anti-A and anti-B antibodies, which means that they cannot receive transfused blood from someone with either type A or B blood.  Blood types are also referred to as being “positive” or “negative” which indicates another type of blood antigen called Rhesus factor.  An article on Rhesus factor can be found here.

So… how do you find out your blood type if you can’t donate blood?  There are home blood typing kits that you can buy online through amazon and they are actually pretty fun little experiments that you can run in your home.  With these kits you will have to prick yourself with a lancet but its really not that painful and certainly its much less painful than actually giving blood at a doctors office or donating blood.

Finally, if you have health insurance or have had your blood drawn at your doctor’s office before you can request this information from them.  Your physician should have a record of your old lab work if you have had any drawn in the last several years.  The only problem with this method is that with some physician’s offices struggling to maintain their existing incomes they have resorted to charging people as much as $15 per page for medical record data and your insurance company will likely charge you a copay if you have not had this type of lab drawn in the past.

If you have additional ways that people can find out their blood type then please comment below and we’ll investigate those methods.