Epidemiology

Incidence

• It is rare in UK, but the fifth most common cause of perinatal mortality.
• The incidence has steadily declined over a 40-year period. It has been found to be significantly associated with induction of labour and multiple pregnancy. In the study referred to, it was noted that there was an increased risk in older, ethnic-minority women and that Caesarean delivery was associated with postnatal amniotic-fluid embolism.
• The last triennial report showed the mortality rate per 100,000 pregnancies was 0.57 (from 0.8 in the previous report).^[2] 
• A prospective, national study of amniotic fluid embolism (AFE) is being undertaken by the United Kingdom Obstetric Surveillance System (UKOSS) and has currently found an estimated incidence in the UK of 1.8 cases per 100,000 maternities.^[3]

The improved quality of autopsy may have resulted in some increase in diagnosis.

Presentation

Initial pulmonary symptoms may be minor. Amniotic fluid embolises to the pulmonary circulation, and the patient responds with the rapid development of a complex constellation of findings with sudden cardiovascular collapse, acute left ventricular failure with pulmonary oedema, disseminated intravascular coagulation and neurological impairment.

The above may give a clue to diagnosis, before collapse and haemorrhage occur.

The classical scenario of amniotic fluid embolism (AFE) involves an older multiparous woman, in advanced labour who suddenly collapses.

It can also occur following:

• Termination of pregnancy.
• Amniocentesis.
• Placental abruption.
• Trauma.
• Caesarean section.
• Delivery - unexpectedly, up to 30 minutes after delivery.

There may be cardiotocographic abnormalities, uterine hypertonus and an obstetric intervention such as artificial rupture of the membranes.^[4]

Diagnosis

High index of suspicion on clinical criteria, as above.

• Symptoms occurring during delivery with high likelihood of collapse and incipient disseminated intravascular coagulation.
• CXR may show pulmonary oedema, acute respiratory distress syndrome (ARDS), right atrial enlargement and a prominent pulmonary artery.
• ECG and arterial blood gases are not helpful.
• Postmortem will reveal fetal squamous cells and hair (lanugo) in the maternal pulmonary circulation.
• In the future, the measurement of complement, which may be activated following amniotic fluid embolism (AFE), or the fetal antigen sialyl-Tn may help to diagnose the condition.^[5] The latter can be measured serologically or by immunocytochemistry on lung tissue but, as yet, is not widely available.

Management

Women with symptoms suspicious of amniotic fluid embolism should be transferred to intensive care as soon as possible, as these women may have a better chance of survival.^[2] 

Treatment is supportive.

General

• Resuscitation with oxygen to maintain normal oxygen saturation. Intubate if necessary.
• Fluids to maintain blood pressure.
• Consider pulmonary artery catheterisation in patients who are haemodynamically unstable.
• Initiate cardiopulmonary resuscitation (CPR) if the patient arrests. If she does not respond to resuscitation, perform a perimortem Caesarean delivery. The Managing Obstetric Emergencies and Trauma (MOET) course recommends Caesarean section delivery of the infant within five minutes of cardiac arrest, to facilitate resuscitation.^[6]
• Continuously monitor the fetus.

Pharmacological

• Dopamine, if a pulmonary artery catheter can be inserted (coagulopathy may prevent this).
• Otherwise, rapid digitalisation needs to be considered.
• Management of coagulopathy with:^[7]
  • Fresh frozen plasma (FFP) for a prolonged aPTT.
  • Cryoprecipitate for a fibrinogen level less than 100 mg/dL.
  • Transfuse platelets for platelet counts less than 20 x 10⁹/L.

Surgical

Uterine artery embolisation has been described in 2 cases, with excellent survival.^[8]

Prognosis

The United Kingdom Amniotic Fluid Embolism Register was established to identify the incidence of the condition and to examine any differences or common factors between survivors and fatalities.^[9] There is mandatory reporting of cases. In reported cases from 1997-2004 the mortality is 37%. Of those who die, a quarter are dead within the first hour and most of the remainder by nine hours after presentation.

Mortality and morbidity

This causes a high level of morbidity for mother and baby. If the patient survives, disseminated intravascular coagulation is a common complication. Typical findings among survivors include:^[10]

• Cardiac arrest.
• Hysterectomy.
• Further laparotomies.
• Subglottic stenosis.
• Persisting neurological impairment.
• Admission to intensive care units.

The majority of women will survive. Hypoxic ischaemic encephalopathy and cerebral palsy are found amongst surviving neonates.