Amniotic Fluid Embolism: What It Is and What Happens

What is amniotic fluid embolism?

Amniotic fluid embolism (AFE) is a rare emergency in labour, during a caesarean or shortly after birth, in which the mother suddenly collapses. The Society for Maternal-Fetal Medicine (SMFM), the US specialist body, describes the typical picture as "a triad of sudden hypoxia and hypotension, followed in many cases by coagulopathy": a sudden drop in oxygen and blood pressure, then a failure of the blood to clot.

The name suggests a blockage, but SMFM describes something different. It says AFE appears to involve a sequence triggered "in certain women by entrance into the maternal circulation of material from the fetal compartment", causing an abnormal inflammatory reaction "similar to the systemic inflammatory response syndrome".

How rare is amniotic fluid embolism?

Very rare. The most reliable figures come from national surveillance systems that collect cases from maternity units across a whole country:

SMFM explains why estimates around the world vary so widely: there is no international agreement on how to diagnose it, so studies count different things.

In the most recent UK and Ireland confidential enquiry into maternal deaths, MBRRACE-UK reported that eight women died following AFE in 2022–2024, a rate of 0.38 per 100,000 maternities, similar to the previous two three-year periods.

Symptoms: what happens

AFE comes on suddenly, and usually in hospital: in the Australian and New Zealand study, 2 of 33 cases happened at home. SMFM says it should be considered in any pregnant or just-delivered woman with sudden collapse or cardiac arrest, seizures, severe difficulty breathing or low oxygen, "particularly if such events are followed by a coagulopathy that cannot be otherwise explained".

• SMFM notes that "a period of anxiety, change in mental status, agitation, and a sensation of doom may precede the event".
• The heart may stop. If the baby has not yet been born, monitoring shows the baby's heart rate falling.
• Severe bleeding follows in many cases because the blood stops clotting. SMFM says disseminated intravascular coagulation, a widespread clotting failure, "is present in up to 83% of cases".

In the national registry SMFM cites, 70% of cases happened during labour, 11% after a vaginal birth and 19% during a caesarean.

There is no test that confirms it. SMFM says AFE "remains a clinical diagnosis", made by recognising the pattern and ruling out other causes such as a heart attack, a blood clot in the lungs, a severe allergic reaction, an anaesthetic complication or eclampsia.

What causes it, and can it be prevented?

It cannot be predicted, and there is no established way to prevent it. SMFM's conclusion is direct: "given the rare and unpredictable nature of amniotic fluid embolism, there are no risk factors sufficiently established to justify any alteration in standard obstetric care."

Studies have found some associations. SMFM lists operative birth (caesarean, forceps or ventouse), placenta praevia, placenta accreta and placental abruption, and says a link with induction "is inconsistently reported". The 2010 UK study did find higher odds with induction of labour, twins or more, and in older women from ethnic-minority groups, and its authors suggested clinicians weigh the risks and benefits of induction and caesarean, since more restricted use might reduce the number of cases. But because AFE is so rare, these links cannot tell you or your team who will have it.

How it is treated

Treatment is immediate, supportive and done by a large team. SMFM's recommendations include:

• immediate high-quality cardiopulmonary resuscitation (CPR) if the heart stops
• a multidisciplinary team including anaesthesia, critical care and maternal-fetal medicine
• immediate birth of the baby if the mother's heart has stopped and the pregnancy is at least 23 weeks, which may save the baby and, in SMFM's words, "in theory may assist in maternal resuscitation"
• support for breathing and blood pressure, avoiding excess fluids
• early testing of clotting and rapid replacement of blood and blood products

In the Australian and New Zealand study, 42% of women needed CPR, 85% received a blood transfusion, 61% were admitted to intensive care and 18% had a hysterectomy to control bleeding.

Survival rate and outcomes

Most women survive. In the larger UK study, 19% of women died, and 7% of survivors had permanent neurological injury. The women who died or were left with injury were more likely to have had a cardiac arrest at the start (83% against 33%).

You will see much higher death rates quoted online. SMFM says estimates of both incidence and mortality "vary widely" because there is no international consensus on diagnostic criteria. The 2010 UK study authors concluded that "high-quality supportive care can result in good maternal outcomes".

For babies, the 2010 UK study found that 5 of 37 babies whose mothers had AFE before birth died. In the Australian and New Zealand study, 2 of 36 babies died.

Afterwards: recovery, support and future pregnancies

Recovery often starts in intensive care: 61% of women in the Australian and New Zealand study were admitted to an intensive care unit. Partners may have witnessed the emergency. NICE recommends that women who have had a traumatic birth and want to talk about it are offered advice and support, that the effect on partners is considered, and that post-traumatic stress disorder after birth is treated with trauma-focused psychological therapy. You can ask for a meeting to go through your notes; our page on birth debriefs explains how, and birth trauma and PTSD covers symptoms to watch for. Partners can find support in when the birth was traumatic for you too.

Another pregnancy. SMFM says the recurrence rate "is unknown but appears to be low": several uneventful later pregnancies and no recurrences have been reported, but the numbers are too small for certainty. A pre-pregnancy appointment with an obstetrician is a reasonable place to plan.

If someone died. MBRRACE-UK carries out confidential review of all maternal deaths in the UK and Ireland, and its findings are used to improve care nationally.

Frequently asked questions

What is the survival rate of amniotic fluid embolism?

In UK national surveillance from 2005 to 2014, 81% of women with AFE survived and 19% died; 7% of survivors had permanent neurological injury. Australia and New Zealand recorded 85% survival in 2010–2011. Estimates elsewhere vary widely because studies define AFE differently.

Can amniotic fluid embolism be prevented?

There is no established way to prevent it. The Society for Maternal-Fetal Medicine says it is rare and unpredictable, and that no risk factor is established well enough to justify changing standard obstetric care. Associations such as induction or caesarean birth cannot identify who will have it, so it cannot be foreseen in an individual pregnancy.

What are the risk factors for amniotic fluid embolism?

Reported associations include caesarean or assisted birth, placenta praevia, placenta accreta, placental abruption, twins and, in one UK study, induction of labour. The US specialist body says the evidence on induction is inconsistent. Because AFE is so rare, these factors do not allow anyone to be identified as at risk in advance.

Can amniotic fluid embolism happen again?

The recurrence rate is not known, but it appears to be low. SMFM reports that several women have had uneventful pregnancies afterwards and no recurrences have been published, while cautioning that the numbers are too small to be sure. Plan any future pregnancy with an obstetrician.