Alloimmunization and HDFN Awareness Day, also known as World Alloimmunization and HDFN Awareness Day, is observed worldwide every March 12. This day aims to highlight a pregnancy complication where maternal antibodies attack the red blood cells of an unborn baby, known as hemolytic disease of the fetus and newborn (HDFN). Maternal alloimmunization occurs when a mother produces antibodies against fetal red blood cell antigens, which can lead to severe health issues for the baby, including anemia and jaundice. The most common form of HDFN is Rh disease, which is preventable through Rho(D) immunoglobulin treatment for Rh-negative mothers. On this day, individuals are encouraged to wear purple, the awareness color for these conditions, and to use the hashtag #empoweredinpurple on social media. Additionally, people can support affected families by donating to relevant organizations. The observance serves to promote research and support for mothers and babies impacted by alloimmunization and HDFN.