Anaphylactoid Syndrome/Amniotic Fluid Embolism
Basics
Description
- 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
Epidemiology
Incidence
- 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
Prevalence
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.
Genetics
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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Citation
Domino, Frank J., et al., editors. "Anaphylactoid Syndrome/Amniotic Fluid Embolism." 5-Minute Clinical Consult, 33rd ed., Wolters Kluwer, 2025. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688196/all/Anaphylactoid_Syndrome_Amniotic_Fluid_Embolism.
Anaphylactoid Syndrome/Amniotic Fluid Embolism. In: Domino FJF, Baldor RAR, Golding JJ, et al, eds. 5-Minute Clinical Consult. Wolters Kluwer; 2025. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688196/all/Anaphylactoid_Syndrome_Amniotic_Fluid_Embolism. Accessed December 30, 2024.
Anaphylactoid Syndrome/Amniotic Fluid Embolism. (2025). In Domino, F. J., Baldor, R. A., Golding, J., & Stephens, M. B. (Eds.), 5-Minute Clinical Consult (33rd ed.). Wolters Kluwer. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688196/all/Anaphylactoid_Syndrome_Amniotic_Fluid_Embolism
Anaphylactoid Syndrome/Amniotic Fluid Embolism [Internet]. In: Domino FJF, Baldor RAR, Golding JJ, Stephens MBM, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2025. [cited 2024 December 30]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688196/all/Anaphylactoid_Syndrome_Amniotic_Fluid_Embolism.
* Article titles in AMA citation format should be in sentence-case
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T1 - Anaphylactoid Syndrome/Amniotic Fluid Embolism
ID - 1688196
ED - Domino,Frank J,
ED - Baldor,Robert A,
ED - Golding,Jeremy,
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BT - 5-Minute Clinical Consult, Updating
UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688196/all/Anaphylactoid_Syndrome_Amniotic_Fluid_Embolism
PB - Wolters Kluwer
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DB - Medicine Central
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