Antiphospholipid Antibody Syndrome - What Is APS?

This Autoimmune Disorder Increases the Risk of Recurrent Miscarriages

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Antiphospholipid antibody syndrome, also known as antiphospholipid syndrome or APS, is an autoimmune disorder in which the body's immune system reacts against certain normal substances present in blood and causes health problems. A woman with APS will have a greater than average tendency to form blood clots and experience miscarriages.

What Causes APS?

Antiphospholipid syndrome is caused by the abnormal formation of anti-phospholipid autoantibodies (aPL).

These proteins in the blood attack a type of fat in all cells called phospholipids. The attacks cause cell damage that leads to blood clots in arteries and veins.

Why aPL form in some people and not others is not well understood. It's possible their production is triggered by environmental factors (like an infection) in people who are already genetically predisposed to them.

APS and Health Problems

People can have anti-phospholipid autoantibodies without having antiphospholipid syndrome. A person is only diagnosed with APS if the antibodies cause health problems.

Anti-phospholipid autoantibodies interfere with blood coagulation. This can cause clots to form, which can stop blood flow in arteries and veins - a dangerous condition known as thrombosis. 

People with APS can have blood clots anywhere in the body, including the heart, brain, legs and lungs.These clots can cause problems such as:

The Link Between APS and Miscarriage

If you have experienced multiple miscarriages you may be tested for APS. This condition is associated with greater odds of pregnancy loss.

An estimated 10 to 25 percent of women with recurrent miscarriages have APS, and a person with APS will often have no other symptoms of the disorder until she experiences recurrent miscarriages.


Several problems in pregnancy can be caused by APS: 

Some controversy exists over whether APS causes early pregnancy losses. Most doctors agree that APS can cause late losses but the evidence is unclear on whether APS causes early losses.

According to the American College of Rheumatology, there are two ways that aPL may cause pregnancy problems:

  • By causing clots in the blood vessels of the placenta. These clots could cause fetal growth retardation. 
  • By directly attack placental tissue. These attacks could block the proper growth and development of the placenta.

Who Gets It?

APS is usually a disease that affects young women. It's five times more common in women than men.

Most people who have APS are diagnosed when they're between 30 and 40 years old. 

ALS is common in people with the autoimmune disorder systemic lupus erythematosus (SLE). Up to 40 percent of people with lupus have anti-phospholipid autoantibodies. Half of this group develops blood clots and/or has miscarriages. 

Testing for Antiphospholipid Syndrome

If you've had recurrent miscarriages, your doctor will test for specific anti-phospholipid autoantibodies called anticardiolipin antibodies or lupus anticoagulant antibodies.

This is part of the normal recurrent miscarriage workup. Testing positive for these antibodies may indicate that you have APS.

How APS Is Treated in Pregnancy

Doctors usually treat the condition by having the woman take low-dose aspirin and injections of a blood thinner called heparin during pregnancy. This course of action has been shown to be safe for mother and baby. It reduces the odds of forming blood clots while increasing the odds of a successful pregnancy.

Also Known As: Antiphospholipid Syndrome, APS


Antiphospholipid Syndrome. The American College of Rheumatology. May 2015.

What Is Antiphospholipid Antibody Syndrome? National Heart, Lung, and Blood Institute. May 17, 2012.

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