Women with infertility problems, particularly recurrent miscarriages, are likely to undergo testing for antiphospholipid antibodies. These are proteins that are produced by the immune system in antiphospholipid antibody syndrome, a disorder that causes blood clots (thrombosis) in both arteries and veins as well, and which can be the cause of some pregnancy-related complications such as miscarriage, stillbirth, preterm delivery, or severe preeclampsia. When these antibodies are produced (cardiolipin or lupus anticoagulant antibodies), they bind to a cell's membrane, making it sticky. This affects blood flow, and may contribute to the formation of blood clots as well as other health issues. Antiphospholipid antibodies are sometimes found in the blood of individuals without any disease process - indeed, in about 2% of normal individuals. Antiphospholipid antibodies can be transiently present in a wide variety of conditions, including some bacterial, viral, and parasite infections. Some drugs can also cause antiphospholipid antibodies to be produced, including antibiotics, cocaine, and quinine.