## Extra protein The rhesus factor is the Rh factor blood test D-antigen protein on the surface of red blood cells. If you have this protein, the Rh factor is positive (Rh+); if not, it is negative (Rh-). If a person with Rh- receives blood with the D-antigen, his or her body will start producing D-antibodies. This can cause the red blood cells to break down. Therefore, rhesus-negative blood of the right group can be transfused to anyone, but rhesus-positive blood is only for people with Rh+. ## Rarely encountered The highest percentage of Rh-negative carriers is 30 % of=== Spanish Basques. For the vast majority of the world’s population, the percentage of Rh-negative people is much lower. ## Allergy tendency People with (Rh-) are more prone to [allergies](https://ul.orna.me/KOge/librarydisease?id=21), especially food allergies. This causes them to be more selective about food preferences. ## Altitude considerations Those who are Rh-negative are better at absorbing oxygen, so they are more adapted to living in high-altitude areas. For example, people in China who are Rh-negative tend to fare better at higher altitudes than lower altitudes. ## Pregnancy considerations The rhesus factor is of key importance when planning a [pregnancy](https://ul.orna.me/KOge/librarydisease?id=3). If both partners are Rh-negative, there will be no problems. But if the man is Rh-positive and the woman is negative, then in most cases their baby will be Rh-positive, which in turn will lead to Rh factor conflict between mother and child. In the first pregnancy, the risk of problems is not too high, but with each subsequent pregnancy, risk increases and requires especially careful monitoring. Despite this, it is not a contraindication for pregnancy — it is just something to keep in mind.