Antiphospholipid syndrome (APS) is a condition that makes the blood clot too easily. This can lead to serious problems such as a stroke, a heart attack, and blood clots in the legs or lungs. During pregnancy, APS can lead to miscarriage and other serious pregnancy problems.

APS is caused by antibodies. Normally, the immune system makes antibodies that attack germs like bacteria or viruses. In APS, the immune system makes abnormal antibodies that affect how the blood clots. These antibodies can be found with a blood test. A person who has these antibodies and has had blood clots is said to have APS.

APS is usually treated with blood-thinning medicine. Treatment and close monitoring are needed during pregnancy.