How come some people produce antiphospholipid antibodies?

Miscarriage. Apa, along with lupus anti-coagulant antibody, are two antibodies that attack the areas in the cell wall of growing tissue, especially the fast-growing placental tissue of an early pregnancy. These are newly-discovered causes for recurrent miscarriage, and are usually treated with Heparin injections and Aspirin during pregnancy. The reason for producing these antibodies is not really known.