The immunoglobulin M (IgM) antibody test for toxoplasmosis is a serological test that detects the body's initial immune response against the parasite Toxoplasma gondii. These antibodies typically appear within the first week after infection, peak within one to two months, and then gradually decline over several months to a year. It is primarily used to differentiate between recent/acute and old/chronic infections, especially in pregnant women and immunocompromised individuals.