Amniotic Fluid Embolism (Anaphylactic Syndrome of Pregnancy): A Rare, Sudden, and Life-Threatening Childbirth Complication — What It Is, Why It Happens, and How It's Treated
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
Editorial note: This article is for general education only. It is not medical advice, a diagnosis, or a treatment plan. Labor emergencies require immediate care by an obstetric team. If you have concerns about childbirth risks, discuss them with your obstetric provider. Amniotic fluid embolism cannot be prevented, predicted, or self-managed.
TL;DR
Amniotic fluid embolism (AFE) — also called anaphylactic syndrome of pregnancy — is a rare, sudden, and life-threatening emergency that occurs when amniotic fluid enters the bloodstream during labor, delivery, or immediately after birth, triggering a severe allergic-type reaction. It strikes without warning, can cause heart and lung failure, cardiac arrest, and severe bleeding, and accounts for roughly 1 in 40,000 U.S. deliveries and up to about 10% of maternal deaths. There is no known cause and no prevention; survival depends on rapid emergency care. Modern studies put the death rate at roughly 10–30%, far lower than the 60%+ figures cited historically.
Quick Answer: What Is Amniotic Fluid Embolism?
Amniotic fluid embolism is a rare, life-threatening complication that happens when amniotic fluid — the liquid surrounding the fetus — enters the birthing person's bloodstream just before, during, or immediately after childbirth, triggering a severe allergic-type reaction. It causes sudden breathing failure, cardiac arrest, and severe bleeding. It affects about 1 in 40,000 deliveries in the United States, has no known cause or prevention, and requires immediate emergency treatment, typically including CPR, blood transfusions, and oxygen support.
What Is Amniotic Fluid Embolism?
Amniotic fluid embolism (AFE) is a rare and life-threatening complication that occurs when a pregnant woman gets amniotic fluid into her bloodstream just before, during, or immediately after childbirth. Amniotic fluid is the liquid that surrounds the fetus in the uterus during pregnancy. It is mostly water, but it also contains fetal cells and tissue.
For reasons that are mostly unknown, some people have a severe allergic response when amniotic fluid mixes with their blood. This reaction can lead to heart and lung failure, which causes a lack of oxygenated blood throughout the body. That can include cardiac arrest — when the heart stops beating. People with AFE may also bleed uncontrollably from the uterus or a C-section incision.
AFE happens suddenly and unpredictably. It is extremely challenging to treat and always requires emergency medical care. Amniotic fluid entering the bloodstream is actually a normal part of the birthing process — in most people, it causes no reaction at all. Researchers still aren't sure why some people react to it this way while others don't.
AFE is also known as anaphylactic syndrome of pregnancy, which reflects the modern understanding that the condition behaves like a severe allergic reaction rather than a physical "embolism" (blockage) in the way the name originally suggested.
How Rare Is Amniotic Fluid Embolism?
AFE is exceptionally rare, which is part of what makes it so dangerous: it happens without warning, and most providers will encounter it only a handful of times in a career. In the United States, it affects approximately 1 in every 40,000 deliveries, and about 1 in every 53,800 deliveries in Europe. Modern registry studies describe incidence of roughly 2 to 8 cases per 100,000 deliveries.
Despite its rarity, AFE carries outsized importance in maternal health. It remains one of the leading causes of maternal death around childbirth — in U.S. data it accounts for roughly 7.5% to 10% of maternal mortality, and it has been described as the second leading cause of peripartum maternal death.
U.S. deliveries affected: 1 in 40,000 (Cleveland Clinic)
European deliveries affected: 1 in 53,800 (Cleveland Clinic)
Incidence (modern range): 2–8 per 100,000 deliveries (Medscape, 2025)
Incidence (NIH StatPearls): 2.2–7.7 per 100,000 deliveries (NIH StatPearls, 2026)
Incidence (U.S. population study): 6.0 per 100,000 deliveries (JAMA Network Open, 2022)
Incidence (France, 20-year study): 4.9 per 100,000 deliveries, stable over time (Eur J Obstet Gynecol, 2024)
Share of U.S. maternal deaths: ~7.5–10% (Medscape, 2025)
To put the numbers in perspective, in a 20-year French national study the incidence held steady at a mean of 4.9 cases per 100,000 deliveries — but the case-fatality rate steadily declined, averaging 17.7% in recent years, showing that recognition and emergency care have measurably improved outcomes.
What Increases Your Risk of Amniotic Fluid Embolism?
Risk factors for AFE are hard to predict precisely because the condition is so rare and difficult to study. Current research points to several possible risk factors, though none of them predicts the condition reliably — most people with these factors never develop AFE, and some who develop it have none of them.
Advanced maternal age: Being older than 35 during pregnancy
Expecting multiples: Twins, triplets, or more
Fetal distress: Changes in the fetal heart rate
Placenta problems: Issues such as placental abruption
Preeclampsia or eclampsia: High blood pressure conditions of pregnancy
Polyhydramnios: Excess amniotic fluid
Cervical tears: Tears during labor
Labor induction: Induction medications or procedures
C-section delivery: Surgical birth
Operative assisted delivery: Forceps or vacuum extraction
An important caveat deserves emphasis: having none of these risk factors does not rule AFE out, and having several does not mean it will happen. AFE remains unpredictable, and that unpredictability is a defining feature of the condition.
What Are the Symptoms of Amniotic Fluid Embolism?
Signs and symptoms of AFE develop suddenly and quickly — often within minutes. They overlap with other serious childbirth complications, such as uterine rupture, placental abruption, and eclampsia, which makes detection harder.
Breathing failure: Shortness of breath or difficulty breathing
Blood pressure collapse: Sudden, severe drop in blood pressure
Fluid in the lungs: Pulmonary edema
Heart rhythm changes: Abnormal heart rate; possible cardiac arrest
Bleeding: From the uterus, C-section incision, or IV sites
Fetal distress: Abnormal fetal heart rate
Mental changes: Agitation, confusion, or sudden anxiety
Chills: Sudden onset chills
The classic clinical picture is a person in labor who suddenly stops breathing, collapses, or begins bleeding massively without an obvious explanation. Every one of these signs is itself a reason to call emergency obstetric help immediately.
What Causes Amniotic Fluid Embolism?
There is no known cause of AFE. The leading theory is that the placenta breaking down during labor or delivery triggers an immune response in some people, leading to the condition. It is not clear why this happens in some people and not in others.
This is why AFE is also called anaphylactic syndrome of pregnancy: modern research increasingly views it as an allergic-type reaction of the immune system to fetal material entering the bloodstream, rather than a mechanical blockage of the lungs by debris, as older theories assumed.
Can AFE Happen During a C-Section?
Yes. Amniotic fluid embolism can occur during both vaginal deliveries and C-section deliveries. While C-section is listed among possible risk factors in some studies, the majority of cases still occur during vaginal birth — largely because most births are vaginal.
How Is Amniotic Fluid Embolism Diagnosed?
Diagnosing AFE is difficult because many of its symptoms overlap with other serious conditions. Your provider will rule out other possible causes while working to diagnose it. AFE typically occurs in labor or within 30 minutes of delivery. If you have AFE, you'll need immediate treatment to avoid potentially fatal complications.
Providers may diagnose AFE if the following symptoms are present:
Sudden drop in blood pressure: Circulatory collapse
Difficulty breathing: Rapid respiratory failure
Irregular heart rate or arrest: The heart stops beating entirely
Unexplained hemorrhage: Severe bleeding with no other explanation
Because AFE is a medical emergency, providers work quickly and cannot rely on imaging or blood tests for a diagnosis — there is no confirmatory test they can run in the moment.
The Two Phases of AFE
Healthcare providers classify amniotic fluid embolism into two stages:
Phase one: Rapid respiratory failure and cardiac arrest — highest fatalities
Phase two: Hemorrhagic phase — excessive, uncontrolled bleeding at the C-section incision or from the uterus — severe bleeding emergency
If a person survives AFE, providers may order follow-up tests once stabilized, including an EKG to check the heart's rhythm, a pulse oximeter to check blood oxygen, a chest X-ray to look for fluid around the heart, and an echocardiogram to see how the heart is functioning.
How Is Amniotic Fluid Embolism Treated?
Amniotic fluid embolism is an emergency, and treatment must happen very quickly to protect both the birthing person and the fetus. There is no cure and no medication that reverses the reaction — treatment is entirely about supporting the heart, lungs, and blood clotting until the body stabilizes.
Immediate delivery of the baby: Emergency C-section if symptoms begin before birth
CPR: Restart the heart during cardiac arrest
Tracheal tube or mechanical ventilation: Oxygen support for breathing failure
Blood, plasma, and platelet transfusions: Multiple transfusions to control hemorrhage
Steroids and other medications: Support blood pressure and heart function
Pulmonary artery or central venous catheter: Monitor blood pressure precisely
Hysterectomy: Surgery to stop uncontrollable bleeding
What's the Survival Rate for AFE?
Because AFE is difficult to diagnose and outcomes depend on so many factors, estimates have varied enormously across decades of research — and older, frightening numbers are still quoted today. Early case series reported death rates as high as 60% or more, and some historic U.K. estimates reached 86%. Modern registry data tell a much less grim story:
Historic estimates (1970s–1990s): 60–86%
Modern U.S. registry analysis (2020): ~10%
U.S. evidence review (2009): 13–30%
Recent range cited by AFE Foundation: 20–60%
France 20-year study (2024): Mean 17.7% and declining
In the largest U.S. registry analysis (160 cases, 2020), the maternal mortality rate was 10%, with 46% of survivors leaving the hospital neurologically intact — meaning slightly more than half of survivors had some degree of neurological impairment at discharge. For the baby, reported perinatal mortality ranges from about 9% to 44%, depending on how far along the labor was when the event began.
Babies delivered after AFE has begun are at risk of not getting enough oxygen, which can cause impairments in the nervous system or brain. If symptoms begin before birth, an emergency delivery may be necessary.
What Are the Long-Term Effects for Survivors?
It depends on how severely a person reacts to AFE as well as their health history. There can be both physical and psychological side effects. Some long-term effects could include:
Neurological damage: Affects memory or word recall
Permanent heart damage: From cardiac arrest
Stroke complications: If a stroke occurred
Kidney problems: From low blood pressure or blood loss
Anxiety and depression: Including feelings of guilt
PTSD: Post-traumatic stress disorder
The national registry data noted above found that only 46% of survivors were neurologically intact at discharge, which is why follow-up neurological care and psychological support are central parts of recovery.
Can Amniotic Fluid Embolism Be Prevented?
Unfortunately, there is no way to prevent amniotic fluid embolism. Healthcare providers are still unsure why AFE happens and what exactly causes the condition.
One way to prepare for any kind of medical emergency is to develop a plan with your family and healthcare providers. Ask your provider about emergency situations and how your medical team approaches them — this can be part of your birth plan. Remember that a birth plan represents the ideal situation: if there is ever an emergency, your healthcare team will need to act accordingly to protect the health of you and the fetus.
If you're pregnant, your chances of developing AFE are very low — roughly 1 in 40,000. Discuss concerns about this rare condition with your pregnancy care provider so they can help ease your worries.
Key Takeaways
Amniotic fluid embolism is a rare, sudden, and life-threatening emergency of labor, delivery, and the immediate postpartum period, affecting about 1 in 40,000 U.S. deliveries (2–8 per 100,000) and accounting for roughly 7.5–10% of maternal deaths. It occurs when amniotic fluid enters the bloodstream and triggers a severe allergic-type reaction — the placenta's breakdown during labor may set this off, but the exact cause is unknown and nothing can prevent it. Symptoms strike without warning: sudden breathing failure, collapsing blood pressure, cardiac arrest, agitation, and massive unexplained bleeding. It unfolds in two phases — respiratory/cardiac collapse, then hemorrhage. Treatment is emergency support: CPR, ventilation, massive blood transfusions, emergency delivery, medications, and sometimes hysterectomy. Modern mortality is roughly 10–30%, far below the 60%+ of older reports, but over half of survivors may have some neurological impairment, and the baby is also at risk.
Call emergency services or alert your labor team immediately if breathing suddenly fails, blood pressure collapses, or severe unexplained bleeding begins during labor or just after delivery.
If you are pregnant and anxious about AFE, talk with your obstetric provider about what your birth team is prepared for — the honest reassurance is that AFE is extraordinarily rare, and modern obstetric emergency teams train for exactly this scenario.
Frequently Asked Questions
1. Can amniotic fluid embolism be prevented?
No. There is no known cause, no way to predict who will be affected, and no preventive measure. AFE occurs unpredictably even in low-risk pregnancies.
2. Is amniotic fluid embolism the same as a blood clot?
No. Despite the word "embolism," modern evidence suggests AFE behaves like a severe allergic-type reaction to fetal material in the bloodstream rather than a physical blockage of blood vessels. Some researchers still use the older name anaphylactic syndrome of pregnancy.
3. How rare is amniotic fluid embolism?
Very rare: about 1 in 40,000 deliveries in the United States, or 2–8 per 100,000 deliveries in modern registries — yet it accounts for roughly 7.5–10% of maternal deaths, making it one of the leading causes of death around childbirth.
4. What are the first warning signs?
Sudden shortness of breath or breathing failure, a sudden drop in blood pressure, agitation or confusion, an abnormal heart rate, and unexplained severe bleeding — usually during labor or within 30 minutes of delivery.
5. Can it happen during a C-section?
Yes. AFE can occur during both vaginal deliveries and C-section deliveries.
6. What are the chances of surviving amniotic fluid embolism?
Modern registries put maternal mortality at roughly 10–30%, far lower than the 60%+ cited in older studies. Among survivors, about 46% leave the hospital neurologically intact; the rest have some degree of neurological impairment.
7. What happens to the baby?
If AFE begins before delivery, an emergency C-section may be necessary. Babies delivered after the event begins can be deprived of oxygen, which may cause nervous system or brain impairments; reported perinatal mortality ranges from about 9% to 44% depending on timing.
8. Can it happen after the baby is born?
Yes. AFE typically occurs during labor or within 30 minutes of delivery — meaning it can begin after the baby is born. Anyone who collapses, cannot breathe, or bleeds severely shortly after birth needs emergency care immediately.
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References
Cleveland Clinic — Amniotic Fluid Embolism (Anaphylactic Syndrome of Pregnancy). Medically reviewed; last updated 10/19/2022.
Medscape eMedicine — Amniotic Fluid Embolism: Background, Pathophysiology, and more (updated 07/24/2025).
Mazza GR et al. (2022). Association of Pregnancy Characteristics and Maternal Outcomes with Amniotic Fluid Embolism (JAMA Network Open).
Conde-Agudelo A, Romero R (2009). Amniotic fluid embolism: an evidence-based review (Am J Obstet Gynecol).
Amniotic Fluid Embolism Foundation — AFE Facts for Clinicians.
Carlson K et al. (2026). Amniotic Fluid Embolism (StatPearls, NIH).
Suissa N et al. (2024). Amniotic fluid embolism: 20-year incidence and case-fatality trends (Eur J Obstet Gynecol Reprod Biol).
NPEU / UKOSS — Amniotic Fluid Embolism Surveillance.
Stafford IA et al. (2020). Amniotic fluid embolism syndrome: analysis of the United States registry (Am J Obstet Gynecol MFM).
Kaur K et al. (2016). Amniotic fluid embolism (J Anaesthesiol Clin Pharmacol).
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