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Antiphospholipid Syndrome (APS)

Antiphospholipid Syndrome (APS) is a rare condition in which antiphospholipid autoantibodies cause blood clots and/or pregnancy complications.  A patient may have antiphospholipid antibodies (aPL) and not have any clinical criteria for APS.  A patient with elevated aPL but NO clinical features of APS, should NOT be considered to have APS.

A patient should be assessed for aPL when considering an estrogen-containing contraceptive and/or prior to or early in pregnancy.

Laboratory and Clinical Features

APS can occur alone or in tandem with other rheumatic disease, most often lupus, and is diagnosed when a patient repeatedly tests positive for aPL antibodies or the lupus anticoagulant and has clinical features of APS. Evaluating for APS is a routine component of the obstetric work-up for patients with recurrent miscarriage (3 or more early losses).

APS Diagnosis

APS diagnosis requires one laboratory criterion and one clinical criterion:

Laboratory Criteria

Patient tests positive for elevated aPL more than once 12 weeks papart, including any of:

  • Lupus anticoagulant
  • Anti-Cardiolipin IgG or IgM >40
  • Anti-beta2 glycoprotein I IgG or IgM >40

Clinical Criteria

Patient has any blood clot (including arterial, venous, or small vessel OR any of the following pregnancy complications:

  • Loss >10 weeks of gestation without other explanation
  • Delivery before 34 weeks due to severe preeclampsia or placental insufficiency
  • 3 or more unexplained consecutive miscarriages before 10 weeks of gestation

Borderline Scenarios 

Some patients may have a clinical scenario that suggests APS but doesn’t technically meet the criteria. They may have two early losses and positive laboratory tests. They may have had a prior late loss or early delivery but only one set of positive laboratory tests. In these challenging situations, providers and patients need to make a shared decision about treatment. Given the limited side effects from treatment from low dose aspirin and low-molecular weight heparin, many providers choose to treat patients with partial APS criteria.

Catastrophic APS 

This is a rare condition in which a patient with highly elevated aPL develops acute thrombosis in multiple organs, leading to a life-threatening condition. Several cases of catastrophic APS have been reported in conjunction with pregnancy. 

Treatment of APS During Pregnancy

Regardless of aPL status, any patient with a prior arterial or venous thrombosis typically receives full anticoagulation treatment during pregnancy as recommended by the American College of Obstetricians and Gynecologists.  During pregnancy, and especially during the first 6 weeks postpartum, all patients have a 4 to 5-fold increased risk for blood clots. This risk is even higher for patients with a prior clot, regardless of the reason for that clot. The patient’s obstetrician typically prescribes anticoagulation medications.

Treatment options for patients with positive antiphospholipid antibodies include the following categories:

Positive APL/No Clinical Criteria

Does not meet APS criteria

  • No treatment OR
  • Low-dose aspirin


Does not technically meet APS criteria

  • Low-dose aspirin
  • May consider prophylactic dose of low-molecular-weight heparin (LMWH) based on the clinical situation

Obstetric APS

No history of thrombosis

  • Low-dose aspirin 
  • Prophylactic dose of low-molecular-weight heparin (LMWH)

Thrombotic APS

With or without pregnancy complications

  • Low-dose aspirin
  • Therapeutic dose of low-molecular-weight heparin (LMWH)