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Amniotic Fluid Embolism

Table of Contents

  • Introduction
  • Aetiology
  • Risk factors
  • Clinical features
  • Differential diagnosis
  • Investigations
  • Management
  • Complications
  • References

Introduction

  • Amniotic Fluid Embolism (AFE) is a rare but life-threatening obstetric emergency caused by entry of amniotic fluid or fetal material into maternal circulation, triggering cardiovascular collapse.
  • Incidence: approximately 2 per 100,000 deliveries.
  • Major cause of maternal collapse with high morbidity and mortality.

Aetiology

  • Exact cause unknown; believed to involve an anaphylactoid reaction to fetal antigens.
  • Progression occurs in two stages:
  • Anaphylactoid reaction causing dyspnoea and hypotension.
  • Coagulopathy and hemorrhage (e.g., disseminated intravascular coagulation - DIC).

Risk Factors

  • Obstetric:
  • Caesarean section
  • Instrumental delivery
  • Induction of labour
  • Uterine hyperstimulation
  • Multiple pregnancy
  • Uterine rupture
  • Prior caesarean section
  • Placental abnormalities:
  • Polyhydramnios
  • Placenta praevia
  • Placenta accreta
  • Placental abruption
  • Maternal factors:
  • Age >35 years
  • Ethnic minority groups
  • Multiparity
  • Eclampsia

Clinical Features

  • Typically occurs during labour or postpartum period.
  • Presents as:
  • Sudden cardiovascular collapse, cardiac arrest
  • Acute dyspnoea and hypoxia
  • Profound hypotension
  • Seizures
  • Maternal hemorrhage
  • Coagulopathy (DIC)
  • If antepartum, may cause acute fetal distress.
  • Diagnosis is one of exclusion in the context of maternal collapse.

Differential Diagnosis

  • Cardiac causes: arrhythmia, myocardial infarction, cardiomyopathy, aortic dissection
  • Respiratory causes: pulmonary embolism, aspiration, anaphylaxis, high spinal block
  • Coagulopathy: eclampsia, HELLP syndrome, hemorrhage, uterine atony, sepsis

Investigations

  • Diagnosis primarily clinical and exclusionary; post-mortem histology of maternal lungs is definitive.
  • Bedside:
  • ECG (may show tachycardia, right heart strain, ST/T changes)
  • Cardiotocography (CTG) for fetal wellbeing
  • Arterial blood gases (hypoxemia)
  • Labs:
  • FBC, U&Es, coagulation profile (look for DIC)

Management

  • Immediate ABCDE approach and urgent senior/critical care involvement.
  • Advanced life support with manual left uterine displacement to reduce aortocaval compression during cardiac arrest.
  • Correct hypotension with IV fluids and vasopressors.
  • Correct coagulopathy with blood products (FFP, platelets, packed red cells) guided by haematology.
  • Consider perimortem caesarean section within 5 minutes of maternal cardiac arrest to improve maternal and fetal outcomes.
  • Transfer to intensive care for supportive management.
  • Report all cases to UK Obstetric Surveillance System (UKOSS).

Complications

  • Maternal:
  • Cardiorespiratory arrest
  • Acute respiratory distress syndrome (ARDS)
  • Cardiac failure
  • Disseminated intravascular coagulation (DIC)
  • Cerebrovascular events
  • Neurological sequelae
  • Death
  • Fetal:
  • Intrauterine or neonatal death
  • Hypoxic ischaemic encephalopathy
  • Cerebral palsy

References

  • UKOSS, Amniotic Fluid Embolism, 2023
  • MBRRACE-UK, Maternal Mortality 2020-2022, 2024
  • BJOG, Maternal Collapse in Pregnancy and The Puerperium, Green Top Guideline No 56, 2020
  • Moldenhauer, Amniotic Fluid Embolism, 2024
  • Antenatal Screening for Down’s Syndrome
  • Antepartum Haemorrhage (APH)
  • Breech Presentation
  • Caesarean Section
  • Cord Prolapse

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