People have molecules called antigens on the surface of their red blood cells. The two most important ones are ABO system antigens and the Rh system.
The ABO Blood Group System
- If you have A antigens covering your red cells, then you have blood group A and you also have B-antibodies.
- If you have B antigens covering your red cells, then you have blood group B and you also have A antibodies.
- If you have both A and B antigens covering your red cells, then you have blood group AB and no A or B antibodies.
- If you have neither A or B antigens covering your red cells then you have blood group O and both A and B antibodies.
The Rhesus (Rh) system
Besides A and B there is another important antigen on red blood cells, the Rh antigen which is also known as the D-Antigen.
- If the Rh antigen is present, then the blood is RhD positive.
- If the Rh antigen is not present, then the blood is RhD negative.
Does the population of Rh-positive people change?
The number of people who are Rh-positive varies by population. Among white Europeans, about 16% of the population will have Rh-negative blood types (and 84% will be Rh-positive). In other populations of the world, the frequency of Rh negative types will be much lower; in Africans, only 9 people in 10,000 will be Rh negative, and in the non-African, non-European portion of the world, only 1 person in 10,000 will be Rh negative.
In the United States, about 15% of the general population is Rh negative; almost 20% of European Americans are Rh negative (because many Americans have western European ancestry), and approximately 5-10% of African Americans are Rh negative (because of the flow of European genes into the African American population). Fewer than 1% of Asian and Native Americans are Rh negative.
Blood Type and Fertility
For the most part, we all associate blood type with health problems and illnesses. Many people don’t pay much attention to their blood type until the time comes when they need to know what it is. In fact, only the people that usually need transplants or transfusions have to worry about their blood type. However, if you’re thinking of becoming pregnant you should think twice about your blood type. Studies show that a woman’s blood type might actually have something to do with her fertility and her ability to get pregnant. Women with blood type O will have a more difficult time getting pregnant than women with any other blood type, especially type A.
Studies show that women with blood type A were more likely to have a lower egg count than women with other blood types, and they were also more likely to have poorer egg quality. On the other hand, women with blood type A in these studies were more likely to have high egg counts and eggs of higher quality than women with other blood types. Another major difference in the fertility levels between blood type O and blood type A is that women with type O do not have well balanced ovarian reserves. In other words, some women’s bodies can keep eggs on hand to come out when necessary, but some women don’t have that ability. So, if you have blood type O, you have a higher chance of needing fertility treatment. The studies do not suggest the reasoning behind these differences. One study suggested that women with blood type O were more likely to seek out fertility treatments to help them conceive since their bodies were not naturally doing so.
While these studies definitely suggest you won’t become pregnant as easily if you have type O blood type, there is always a chance you’ll prove the statistics wrong. Even the doctor that directed the most convincing study on the topic explained that age is still the most accurate predictor of a woman’s fertility, and blood type might only be a coincidental association. Women with type O blood type should not assume that they are infertile but based on statistics they should be more mentally prepared to take on the burden than women with other blood types. If you’re concerned about your blood type affecting your ability to conceive speak with your doctor about fertilization treatments.
Source: Edward J. Nejat et al: Implications of Blood Type for Ovarian Reserve. Human Reproduction Volume 26 Issue 9 pp. 2513-2517 2011