Antiphospholipid Syndrome (APS)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated July 27, 2026

Antiphospholipid Syndrome (APS) is an acquired autoimmune disorder in which the immune system produces antibodies against phospholipid-binding proteins, creating a hypercoagulable state that damages placental blood flow and causes thrombotic events. The three characteristic antibodies are lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies.¹

Diagnosis requires both a clinical event and laboratory confirmation. The 2006 Sydney criteria, still the framework most clinicians reference day to day, define the clinical event as vascular thrombosis or a recognized pattern of pregnancy morbidity: three or more unexplained consecutive losses before ten weeks, one or more unexplained losses after ten weeks, or one or more preterm births before thirty-four weeks due to eclampsia, severe preeclampsia, or placental insufficiency. Laboratory criteria require at least one characteristic antibody confirmed on two separate occasions twelve or more weeks apart. A single positive test is not sufficient for diagnosis.² In 2023, the American College of Rheumatology and the European Alliance of Associations for Rheumatology published updated classification criteria built on a weighted, additive scoring system, requiring antibody positivity within three years of the clinical event. Both the 2023 criteria and the 2006 Sydney criteria remain in active clinical use.

In pregnancy, APS-driven clotting in the placental vasculature disrupts nutrient and oxygen delivery to the developing embryo. This mechanism underlies APS-associated recurrent pregnancy loss, fetal growth restriction, and late pregnancy loss. APS is one of the most clearly defined and treatable immune causes of recurrent pregnancy loss.

Anticoagulation during pregnancy reduces thrombotic injury to the placental vasculature. Major reproductive medicine guidelines support anticoagulant therapy for obstetric APS.¹ The specific approach is individualized based on clinical history, antibody profile, and the evaluation of the treating clinician.

Women with APS who have experienced pregnancy loss are not experiencing unexplained loss. They have a diagnosable, treatable condition. RRM clinicians evaluate for APS as part of a thorough recurrent pregnancy loss workup. Related conditions include autoimmune and thrombophilic disorders, inherited thrombophilias, and natural killer cell dysregulation.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.