Rh isoimmunization, also known as Rh incompatibility or Rh sensitization, is a condition that arises during pregnancy when a woman's immune system responds to a specific red blood cell antigen that originates from the biological father. This antigen, referred to as the Rh factor, is unfamiliar to the mother and is inherited by the developing fetus.In simpler terms, when the mother and the father have different Rh blood types (e.g., one is Rh-positive and the other is Rh-negative), there is a potential for the mother's immune system to recognize the Rh factor as foreign and mount an immunological response. This immune reaction can lead to the production of antibodies against the Rh factor, posing a risk to the fetus, particularly in subsequent pregnancies.The consequences of Rh isoimmunization can range from mild to severe, with the potential to impact the health of the unborn baby. Therefore, monitoring and appropriate medical interventions are crucial to manage and prevent complications associated with Rh isoimmunization during pregnancy. Doppler study of MCA-PSV screens for fetalanemia in Rh alloimmunization cases, replacing invasive methods like amniocentesis. It's a non-invasive approach utilizing Doppler ultrasound to measure blood flow velocity in the middle cerebral artery, providing early detection without the need for more invasive procedures.