Q: What is Rh factor? I have a 4-year-old son. My blood group is B+ and my husband's is O-. Will this lead to any complication if we plan for another baby?

A:The Rh (rhesus) factor is a protein (antigen) present on the surface of red blood cells (RBCs). As it was first discovered in the rhesus monkey, it has been so named. Individuals carrying this antigen are called Rh-positive (Rh+) blood group type while those lacking it are Rh-negative (Rh-). Rh incompatibility (or Rh disease) is a state in which a woman with Rh-negative blood group is exposed to Rh-positive RBCs leading to the formation of antibodies against this protein (called Rh antibodies). This process of Rh sensitisation can occur when an Rh-negative woman is carrying an Rh-positive baby or if an Rh-negative woman receives blood transfusion containing Rh-positive cells. In either case, her immune system is exposed to the Rh antigen (which is foreign to her body) and begins producing Rh antibodies. The problem of Rh incompatibility is of clinical importance only in a pregnant woman or if blood transfusion is required. These circulating antibodies in a woman's blood are otherwise harmless. As you are Rh+, Rh isoimmunisation is of no concern in your case as it occurs only in women who are Rh-.