How Antiphospholipid Antibody Syndrome Affects Pregnancy

Smiling pregnant female patient waiting in clinic examination room

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Antiphospholipid syndrome (APS) is a rare autoimmune condition that causes the immune system to attack phospholipid-bound proteins in blood cells and the lining of blood vessels. If you haven’t taken a recent course in college biology (and most of us haven’t), phospholipids are a necessary component of human cells.

When their function is impaired in APS, normal blood clotting can be affected. Because of this, people with APS may face pregnancy complications that require close monitoring and treatment.


When APS antibodies prevent proteins in the blood from binding to phospholipids, the normal balance between bleeding and clotting is upset. This can result in the blockage of blood flow and the formation of blood clots, which can lead to deep vein thrombosis, strokes, and heart attacks if left untreated.

Like many other autoimmune conditions, the cause of APS is unknown. Medical experts believe that genetics and infections may both play a role. Smoking also appears to raise the risk of developing APS.

This condition can be diagnosed as a stand-alone disease (called primary APS), or it may occur along with another autoimmune disease (such as lupus). In this case it is called secondary APS. 


Antiphospholipid (APL) antibodies are present in about 1% to 5% of healthy people and 20% to 40% of those with lupus. An estimated 75% to 90% of APS patients are women.

An estimated 30% to 50% of people with APS will ultimately be diagnosed with a second autoimmune disease.

Relationship to Recurrent Miscarriages

APS accounts for approximately 15% of recurrent miscarriages, with half of those losses occurring in the first trimester. While the reason for APS-associated miscarriages is unclear, some researchers believe that the blood clots seen in APS can block the blood supply to the placenta.

APS is a well-established cause of later miscarriages, but doctors are still unsure of the role that aPL antibodies might play in early miscarriage.

Other pregnancy complications that are linked to APS include:


Most people who have aPL antibodies have no symptoms. For women, recurrent miscarriages may be the only symptom.

In rare cases, patients may develop catastrophic anti-phospholipid syndrome (CAPS), in which major blood clots form over a period of days, resulting in acute blockage of vessels that requires immediate medical attention.

If you experience any of the following symptoms of a blood clot, call your doctor or 911:

  • Pain, numbness, or unusually pale skin in an arm or leg
  • Shortness of breath
  • Swelling or redness in a leg


APS testing is not a routine screening during pregnancy; rather, it is only done in people who have had unexpected blood clots or recurrent miscarriages.

Blood Tests for APS

If your doctor suspects APS, they may run two types of tests:

  • Blood clotting tests to check for lupus anticoagulant
  • Antiphospholipid antibody (aPL) tests, which can include anticardiolipid antibody and/or antibodies to beta-2 glycoprotein 1

Either a positive blood clotting test or a positive aPL test can result in an APS diagnosis, but only if the person also has symptoms such as blood clots and/or repeated miscarriages.

Generally, when considering APS as a possible factor in recurrent miscarriages, doctors look for a person to be positive for lupus anticoagulant or aPL on more than one occasion before making a diagnosis.

Diagnosing APS can be a challenge because the standard tests for lupus anticoagulant antibodies are somewhat unreliable. In addition, sensitivity can vary based on the agent used in each laboratory.

Treatment and Prognosis

Women who have been diagnosed with APS have about a 70% chance of a successful pregnancy with treatment, which usually consists of low-dose aspirin and/or heparin injections.

While this treatment improves pregnancy outcomes, it can increase the rates of third-trimester pregnancy complications. Because of this, people with APS are usually seen by a high-risk OB/GYN during pregnancy for monitoring and treatment.

Those who have a second autoimmune disease will need to be followed by their rheumatologist as well.

Because APS can be associated with other health concerns, OB/GYNs often advise women who have tested positive for the condition to consult with a specialist for monitoring of the condition after pregnancy.

Some OB/GYNs advise against the use of hormonal contraception in women with APS because of the added risk of blood clots. A long-acting intrauterine device (IUD) is often recommended instead.

With long-term treatment for APS, recurrent blood clots can be avoided and patients can look forward to a long and healthy life.

6 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. National Library of Medicine. Antiphospholipid syndrome - APS.

  2. Antovic A, Sennström M, Bremme K, Svenungsson E. Obstetric antiphospholipid syndrome. Lupus Sci Med. 2018;(5)1:e000197. doi:10.1136/lupus-2016-000197

  3. APS Foundation of America. Frequently asked questions (FAQ).

  4. Di Prima FA, Valenti O, Hyseni E, et al. Antiphospholipid Syndrome during pregnancy: the state of the art. J Prenat Med. 2011;(5)2:41-53. PMID:22439075

  5. University of Michigan. Antiphospholipid syndrome program.

  6. Sammaritano LR. Contraception in patients with systemic lupus erythematosus and antiphospholipid syndrome. Lupus. 2014;23(12):1242-1245. doi:10.1177/0961203314528062

Additional Reading
  • University of Illinois – Urbana/Champaign, "Antiphospholipid Syndrome." Patient Resources.

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.