Amniotic Fluid Embolism

Introduction

Amniotic fluid embolism (AFE) is a rare yet well-recognised cause of maternal collapse.

It is a complication of either foetal tissue or amniotic fluid entering maternal pulmonary circulation, resulting in cardiovascular compromise.

The UK Obstetric Surveillance System (UKOSS) found the incidence of AFE to be as high as 2:100,000 deliveries in their 2010 report, with a further study taking place over the next 3 years.¹

Aetiology

The aetiology behind AFE remains unknown, but it is believed to involve either a complement or anaphylactic reaction to foetal material.³

There are 2 proposed stages:⁴

• Anaphylactoid reaction to foetal antigens (dyspnoea & hypotension)
• Coagulopathy & haemorrhage

Risk factors

Table 1. Suggested risk factors for amniotic fluid embolism.

Clinical features

AFE may occur in labour or throughout the post-partum period. The majority of cases occur during labour.

Clinical findings are often non-specific and may mimic other major causes of maternal collapse (e.g. eclampsia), so AFE will often be a diagnosis of exclusion.

The most common presentation is acute cardiovascular collapse and cardiac arrest. Other features may include:

• Seizures
• Profound hypotension
• Maternal haemorrhage
• Acute dyspnoea and hypoxia
• Coagulopathy including disseminated intravascular coagulation (DIC)

If AFE occurs before delivery, acute foetal distress may occur.

Differential diagnoses

As described above, AFE is usually a diagnosis of exclusion. It is important to consider other causes of maternal collapse:

• Sudden cardiac arrest in young women: arrhythmia, myocardial infarction, congenital heart disease, cardiomyopathy, aortic dissection
• Respiratory arrest: pulmonary embolism, aspiration, anaphylaxis, high spinal block
• Coagulopathy: eclampsia, HELLP syndrome, haemorrhage, uterine atony, sepsis

Investigations

Post-mortem histology sampling is the only definitive method of diagnosing AFE (presence of foetal squamous cells in maternal lungs).

Bedside investigations

Relevant bedside investigations include:

• ECG: tachycardia, right heart strain, ST segment & T wave changes
• Cardiotocograph (CTG) to assess foetal wellbeing
• Arterial blood gas: hypoxaemia

Laboratory investigations

Relevant laboratory investigations include:

• Baseline blood tests: including FBC, U&Es, clotting profile, group & save, troponin

Management

This is a life-threatening emergency, so intensive respiratory and haemodynamic support with the replacement of clotting factors is required urgently for the mother.

Immediate delivery of the foetus can greatly improve both foetal and maternal mortality.

Resuscitation

All mothers should be assessed with an ABCDE approach, and senior clinicians should be called. Patients will require early critical care input.

Patients in cardiac arrest should undergo advanced life support with a manual uterine left tilt to reduce aorto-caval pressure.

Consider major obstetric haemorrhage

Correct hypotension with fluids & blood products.

Correct coagulopathy with fresh frozen plasma, platelets or packed red cells with advice from haematology.

A perimortem caesarean section should be considered within 5 minutes of arrest to improve maternal & foetal outcomes.

Supportive care

Following resuscitation women will require transfer to intensive care. Infants will need to be admitted to the neonatal intensive care unit.

Cases of AFE should be reported to the UKOSS national register.

Complications

AFE is the 10^th leading cause of maternal mortality.²

Maternal complications include:

• Cardiorespiratory arrest
• Acute respiratory distress syndrome
• Cardiac failure
• Disseminated intravascular coagulopathy
• Cerebrovascular events
• Neurological sequelae.
• Death

Foetal complications include:

• Intrauterine or neonate death
• Cerebral palsy
• Hypoxic ischaemic encephalopathy

Key points

• Amniotic fluid embolism occurs when fetal material or amniotic fluid enters maternal pulmonary circulatiom
• The typical presentation is acute dyspnoea, profound hypotension, shock and cardiac arrest with coagulopathy
• Risk factors include ageing, caesarean section, induction of labour, multiple pregnancy, polyhydramnios, uterine hyperstimulation, placental disorders and uterine rupture
• Amniotic fluid embolisms are often a clinical or post-mortem diagnosis, but the presence of foetal squames found in maternal lungs is the only definitive diagnosis
• ABCDE assessment is crucial, with an urgent caeseran section if haemodynamically unstable
• Maternal complications include blood clotting derangement, organ dysfunction and death
• Foetal complications include hypoxic ischaemic encephalopathy and death

Reviewer

Mr James Tibbott

Consultant Gynaecologist

Editor

Dr Chris Jefferies

References

1. UKOSS, Amniotic Fluid Embolism, 2023, Available from: [LINK]
2. MBRRACE-UK, Maternal Mortality 2020-2022, January 2024, Available from: [LINK]
3. BJOG, Maternal Collapse in Pregnancy and The Puerperium, Green Top Guideline No 56, April 2020, Page 23, Available from: [LINK]
4. Tuffnell, Tibbott, Chipeta, Amniotic Fluid Embolus, Cambridge University Press May 2021, Available from: [LINK]
5. Moldenhauer, Amniotic Fluid Embolism, January 2024, Available from: [LINK]