There are “blood type” diets, “blood type” personalities, and even “blood types” that are tastier to mosquitos (apparently if you are type O, you should go out and buy some more bug spray!). And while most of us have no idea what A, B, AB, or O mean until we visit our first American Red Cross blood drive, your blood type is actually pretty important in the land of obstetrics. Although most of us don’t think past those three letters (and four groups), the plus or minus that comes after the A, B, AB, and O is equally as important as the letter. The negative or positive denotes the Rh factor. If there is a mismatch between the negative and positives in a pregnant woman, just like those AA batteries you are always in need of, this system won’t work the way it is supposed to.

Let’s start with the simple stuff…

1. There are four basic blood groups; A, B, AB, and O. What distinguishes A from B or AB from O are the antigens (a.k.a. the proteins) on the surface of red blood cells.

2. The symbol, plus or minus, which follows the letter is referring to the presence (+) or absence (-) of the Rh factor. Rh stands for rhesus, and Rh or Rhesus factor is another antigen that is found on red blood cells. Rh antigen is present or + in Rh (+) individuals and absent or – in Rh (-) individuals.

Moving on to a couple of fun facts that will make you look smart at a cocktail party…

3. The most common blood type is O+.

4. The universal blood donor (you can give to anyone) is blood type O-.

5. The universal blood recipient (a.k.a. you can take from anyone) is AB+.

6. You inherit your blood type from your parents, and you will pass your blood type on to your children.

Last, the essential stuff for anyone who has been or will be PREGNANT….

7. Rh-negative women need special attention. If untreated AND pregnant with an Rh-positive baby, they have the potential of forming antibodies against the Rh factor that is covering their baby’s red blood cells. And while this may not be a big deal in their current pregnancy (antibodies are like Rome; they were not built in a day), it will be a major deal in future pregnancies. Therefore, all Rh-negative women should receive a medication called RhoGAM (a.k.a. RhoD or Rh immune globin) during their pregnancy to prevent the formation of these antibodies.

8. RhoGAM is an injectable medication that contains a small amount of antibodies pooled from blood donors…it works to kill off any Rh-positive blood cells lingering in the immune systems of Rh-negative women. Think of RhoGAM as a stun gun to the immune system of an Rh-negative pregnant woman. Basically, it will “daze and confuse” her immune system so that she doesn’t have a chance to make antibodies to the Rh factor her body is seeing during pregnancy. Problem solved. And in the past, this was a big problem that not only cost a lot of perinatal morbidity but also mortality. So kudos to those who racked their brains and “birthed” RhoGAM.

9. When it comes to most things pregnancy, it takes two to tango. Therefore, just because you are Rh-negative doesn’t mean that your baby will be. If your partner is Rh-positive, there is a good chance your little one will be too (and that’s when you have a problem on your hands)! To be safe, all Rh-negative women will be given RhoGAM during pregnancy (remember, we won’t know your little one’s Rh factor until birth). The good news is that the majority of pregnant women will only need to roll up their sleeves and stick out their arms twice, once at 28 weeks and once following delivery. This is because in most cases maternal and fetal blood don’t say, “It’s nice to meet you” until delivery. However, because this introduction may speed up to the third trimester in about 2% of pregnant women, we give a precautionary dose at 28 weeks.

10. Unfortunately, two times may not be the “RhoGAM charm.” If bleeding should occur during the pregnancy or if you undergo an invasive procedure such as a CVS or an amniocentesis, your blood and your baby’s blood might get mixed up. Therefore, to be extra careful, we recommend you get another shot within 72 hours of the bleeding or the procedure.

11. Rh-negative women that are NOT given RhoGAM are at serious risk during their NEXT pregnancy. So while many of us have the “I will deal with that tomorrow” attitude when it comes to things that don’t impact us immediately but can hurt us in the future (think not paying your bills and dealing with your credit score later), you really shouldn’t mess around with RhoGAM. Antibodies to Rh take some time to form. Therefore, while your current passenger might pass through without a problem, the next baby on board could be at serious risk if a woman is NOT given RhoGAM during the current pregnancy. Don’t push this one to the side; this sort of credit your next child can’t afford!

Given that 85% of individuals are Rh+, this incompatibility issue does not come up every day. Simply stated, most moms and their babies are in sync when it comes to Rh status. However, given the serious impact an untreated Rh mismatch can have on a woman and her future children, it is something that we OBs get pretty pesky about. We have to be doubly POSITIVE so that nothing NEGATIVE happens. And while we can’t validate the stuff out there which suggests that As may be “more responsible and patient” while Bs are more “passionate and creative,” we can tell you that your blood type means a lot for your baby (and the babies that you may have to come). That much, we are triply super positive about!