IgG antibodies, or immunoglobulin G, are the most abundant type of antibody in the bloodstream, playing a crucial role in the immune response by neutralising pathogens and facilitating their removal. In clinical practice, measuring IgG levels can help diagnose infections, autoimmune diseases, and immunodeficiencies. A key association is their role in passive immunity, as maternal IgG antibodies are transferred to the fetus, providing early protection against infections.