Toxoplasma gondii is a parasitic protozoan that can cause toxoplasmosis, a disease that can affect the brain, eyes, and other organs. The IgG test for Toxoplasma gondii is a blood test that measures the level of immunoglobulin G (IgG) antibodies in the blood, which are produced by the body in response to the infection. The test can help determine if a person has been infected with Toxoplasma gondii in the past, as IgG antibodies can persist in the blood for many years. However, a positive IgG test does not necessarily mean that a person currently has an active infection, as the antibodies can remain in the blood even after the infection has been cleared. The IgG test is important for pregnant women, as infection with Toxoplasma gondii during pregnancy can cause serious health problems for the fetus.