Amniotic fluid embolism: what it is, how common it is and outcomes

Amniotic fluid embolism (AFE) is a rare obstetric emergency. It typically presents as a sudden collapse of the mother around the time of labour or birth, with problems affecting the heart, lungs and blood clotting.

UKOSS, which is based at the National Perinatal Epidemiology Unit in Oxford, defines cases for surveillance using either a clinical diagnosis or a pathological one. The clinical definition is acute hypotension or cardiac arrest, acute hypoxia or coagulopathy in the absence of any other potential explanation for the symptoms and signs. The pathological definition is the presence of fetal squames or hair in the lungs.

Because there is no single test that confirms it during life, doctors diagnose AFE when a woman has this pattern of sudden collapse and no other cause is found. This is why numbers vary between studies and countries.

UKOSS reports that estimates of incidence vary between 1 in 8,000 and 1 in 80,000 pregnancies, and that estimates of the mortality rate vary widely too, from as much as 86% to more recent estimates of 16% to 30%. The variation reflects different definitions and how cases are identified.

A pooled analysis from five countries including the UK, led from Oxford and published in PLOS Medicine in 2019, estimated the incidence of AFE at 0.8 to 1.8 per 100,000 maternities depending on the case definition. In other words, it is extremely uncommon, and most pregnant women will never encounter it.

UKOSS says no clear risk factors are identifiable from previous cases, though some preliminary evidence suggests that earlier diagnosis may lead to better outcomes. The multicountry study using UK and Australian control data found that some factors were associated with higher odds of AFE. Association is not the same as cause, and none of these factors means that AFE will happen.

AFE is a sudden event. The UK definition describes acute hypotension or cardiac arrest, acute hypoxia, and coagulopathy, which means the blood fails to clot properly and bleeding can follow. The multicountry study found that women who died were more likely to present with cardiac arrest than those who survived.

Because it is an in-hospital emergency, there is no self-management advice. Any woman in labour or soon after birth who suddenly becomes breathless, unwell or collapses needs immediate help from the maternity team. Outside hospital, such as after a home birth, 999 should be called.

The researchers behind the multicountry study concluded that when AFE is suspected, initial supportive obstetric care is important, and that having an obstetrician and anaesthetist present at the time and interventions to correct coagulopathy, including an adequate dose of tranexamic acid, may be important to improve maternal outcome.

In practice this means a team approach: resuscitation if the heart stops, support for breathing and circulation, treatment of bleeding and clotting problems, and delivery of the baby if the woman is still pregnant. Intensive care is often needed for women who survive the first stage.

UKOSS says there is some evidence that fatality is decreasing in the UK. The multicountry study, which pooled data from Australia, France, the Netherlands, Slovakia and the UK, reported that the proportion of women with AFE who died or had permanent neurological injury ranged from 30% to 41%, depending on the case definition.

This means many women survive, and some have lasting effects. Recovery after an AFE may involve intensive care, rehabilitation and psychological support for the woman and her family, and babies may also need neonatal care.

Emotional recovery matters as much as physical recovery. It is reasonable to ask the maternity service for a debrief so that you can ask what happened and what it means for future pregnancies.

Women who have survived AFE, and families who have lost someone, often ask about the chance of recurrence and whether another pregnancy is safe. The sources reviewed for this page do not give figures for recurrence, so this is a conversation to have with an obstetrician, ideally in a debrief or pre-pregnancy appointment after the event.

Local maternity services can advise on support for bereaved families, peer support and counselling. A GP can also help with referrals for mental health support.

AFE is managed as an emergency in the unit where the woman is giving birth, whether NHS or private.

Surveillance through UKOSS and confidential enquiries into maternal deaths is how the UK learns from cases. Anyone who has experienced AFE can ask the trust for a debrief and for information about how their case was reviewed.