Anaphylactoid Syndrome/Amniotic Fluid Embolism



  • Amniotic fluid embolism (AFE) is a syndrome associated with cardiorespiratory collapse during pregnancy or shortly after delivery.
  • Classically includes a triad of hypoxia, hypotension, and coagulopathy surrounding labor and delivery



  • Varies widely because of lack of diagnostic criteria
  • 1.2 to 7.7 per 100,000 deliveries in the United Kingdom, Canada, and United States

Difficult to assess because this is a rare event

Etiology and Pathophysiology

  • Incompletely understood
  • Amniotic fluid enters maternal circulation through disruption of uterine vessels.
    • Causes an abnormal activation of proinflammatory mediators in susceptible patients, leading to cardiopulmonary arrest similar to anaphylaxis or systemic inflammatory response syndrome
    • However, fetal cells can also be found in maternal pulmonary artery samples following normal delivery without AFE.
  • Hemodynamic response not caused by pulmonary vasculature obstruction. Instead, an initial period of pulmonary and systemic hypertension (HTN) is followed by:
    • Pulmonary vasoconstriction, resulting in severe pulmonary HTN, VQ mismatch, and hypoxia
    • Acute cor pulmonale: right ventricular failure with ventricular dilation and deviation of the interventricular septum
    • Impaired left ventricular filling and myocardial ischemia causing left ventricular failure as the dominant hemodynamic alteration
  • Coagulopathy present in 83% of patients (1), but incompletely understood
    • Amniotic fluid can induce platelet aggregation, lead to release of platelet factor III, activate factor X, and the complement cascade.
    • Tissue factor in amniotic fluid can induce thrombocytopenia in animal models, but it is unclear if any of these factors are present in large enough quantities to induce such a significant coagulopathy.
    • Disseminated intravascular coagulation (DIC) results with potential for massive hemorrhage.

A genetic component has not been identified.

Risk Factors

Large population-based studies have identified several risk factors:

  • Medical induction of labor
  • Maternal age ≥35 years old
  • Multiple gestation
  • Cesarean section prior to development of symptoms
  • Cervical laceration or uterine rupture
    • Causality of association with operative vaginal delivery or cesarean section is not always clear.
  • Placental abruption

General Prevention

No identified measure known to reduce the risk of AFE

Commonly Associated Conditions

  • Cesarean section: Strong association with AFE as emergent cesarean may be required for delivery given fetal distress; may be causative in some cases
  • DIC: consumptive coagulopathy that is often a component of the initial presentation of AFE

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