What Causes Amniotic Fluid Embolism?

Originally published 04/04/2022. Updated for accuracy and relevancy on 11/17/2023.

By OBGYN and fertility specialist Dr. Mare Mbaye

Amniotic fluid embolisms (AFEs) are an unpredictable, catastrophic complication of pregnancy. [1] While they are rare, occurring in around 1 in 40,000 deliveries per year, amniotic fluid embolisms are still an important diagnosis for birthers to be aware of. [2] 

What Is An Amniotic Fluid Embolism (AFE)?

When an amniotic fluid embolism occurs, amniotic fluid (the fluid that surrounds the baby in the uterus during pregnancy), fetal cells, or fetal hair enters into the maternal blood circulation. [1-2] These particles then travel somewhere else in the body where they can then cause serious health issues for both parent and child.

What Causes Amniotic Fluid Embolism?

There is a lot that still needs to be learned about amniotic fluid embolisms; they are considered an unpredictable and unpreventable event with no clearly known cause. [1-2] Amniotic fluid embolisms can happen in healthy women at various points in pregnancy, delivery, and postpartum. They have been reported to occur [1-2]:

• During labor
• During a normal vaginal delivery 
• During a normal cesarean section
• During second-trimester abortion procedures
• After abdominal trauma
• Up to 48 hrs after delivery 

The causes behind amniotic fluid embolisms are not really understood at this point. There are several theories, including those that suggest a more immune response as opposed to an embolism in the bloodstream. [3] With this type of response, an amniotic fluid embolism is a reaction that is more similar to anaphylaxis, a severe and sometimes life-threatening allergic reaction. 

Another theory speculates that amniotic fluid embolisms are more akin to septic shock, a condition where the body’s organs begin failing due to a severe infection. [4] The later clinical findings of an amniotic fluid embolism and septic shock do share some commonalities that suggest a similar underlying mechanism. Those who support this theory suspect that amniotic material (like an embolism) causes a blockage or triggers a response in the lungs that sets off a cascade ultimately leading to organ failure and/or death if not caught and managed early. [5] Learn about the symptoms of AFE.

AFE Risk Factors

Even though AFE is rare, you may want to know its risk factors to best inform yourself. While we can’t really predict amniotic fluid embolisms, there are several risk factors that have been identified. These include:

• Older maternal age
• Multiples pregnancy (twins, triplets, etc.)
• Induction of labor
• Intense contractions during labor
• Cesarean section
• Multiparity (having had more than one child)
• Abdominal trauma
• Polyhydramnios (high amount of amniotic fluid)
• Placenta previa
• Eclampsia
• Tears in the uterus or cervix
• Placental abruption (early separation of the placenta from the uterine wall)

Amniotic Fluid Embolism and Delivery

Amniotic fluid embolisms can typically occur during labor, soon after vaginal or cesarean delivery, or during second-trimester dilation and evacuation procedures. [2] They can also occur up to 48 hours after delivery. [6] A 1995 analysis of the US national registry revealed that the majority of amniotic fluid embolisms occur during labor (70%). [6] Of the rest, 19% occurred during cesarean delivery while 11% occurred during a vaginal delivery. 

Operative vaginal deliveries, meaning vaginal deliveries that require assistance with either forceps or a vacuum, and inductions of labor also seem to increase the risk of amniotic fluid embolisms over unassisted and spontaneous vaginal deliveries. [7]

The reasons why inductions of labor, operative vaginal deliveries, and cesarean deliveries have an increased risk of amniotic fluid embolisms are not fully understood. However, those risks are always important to consider when making an informed decision about your delivery mode.

Complications of Amniotic Fluid Embolism

Amniotic fluid embolisms are considered a medical emergency. Reported rates of death have been as high as 86%, with about 50% of these patients dying very quickly, usually within the first hour after symptoms begin. [8-9] These survival rates have improved significantly over the past few decades as the detection methods and medical interventions have been refined. [10] 

Despite these improvements in survival, there is still a high rate of complications for those who do survive. [2] Few patients survive an amniotic fluid embolism with no long-term concerns, there is a high risk of complications like neurological problems. [2] This depends on if and for how long a patient has little to no oxygen to the brain. Complication rates are still high and include severe health consequences such as:  

• Brain injury: Blood clots in the lungs from the embolism can reduce the amount of oxygen traveling to the brain, which can result in permanent brain damage.
• Disseminated intravascular clotting (DIC): A systemic process with the potential for causing thrombosis (blood clots) and hemorrhage (excessive bleeding usually requiring transfusion of blood and other products) [11] 
• Sudden cardiac arrest: The effects of AFE can develop so rapidly that the blood clots in the lungs send the birther into cardiac arrest. [12]
• Multiple organ failure: As the condition progresses, it can start to cause organs like the kidneys or lungs to fail from lack of oxygen in the blood.
• Maternal death

Recognizing this diagnosis quickly and accurately is critical to a patient’s care and to retaining as much quality of life as possible. For patients who do survive an amniotic fluid embolism, the majority will have long-term neurological deficits. Long-term effects can include [13]:

• Memory loss
• Organ failure
• Heart damage that can be temporary or permanent
• Nervous system problems affecting the brain or nerves
• Need for a partial or complete hysterectomy
• Damage to the pituitary gland
• Emotional consequences, especially if the baby does not survive

Fetal Outcomes

Fetal outcomes after an amniotic fluid embolism vary somewhat based on the gestational age–babies that are further along tend to have better outcomes. However, the overall survival rate is close to 70%, which is much more promising than the maternal rate. [8]The neurologic status of the baby is directly related to the amount of time that has gone by from when the amniotic fluid embolism causes maternal arrest and when the baby is delivered (i.e., the faster the better). Fetal complications can include:

• Fetal distress: an amniotic fluid embolism can affect the labor process causing the baby to become distressed. This can potentially lead to other complications if not dealt with appropriately.
• Fetal hypoxia (oxygen deprivation), which can then result in permanent brain damage and conditions like cerebral palsy [14]
• Infant death: If the baby is deprived of oxygen for too long and/or is not delivered quickly enough, the baby can die during delivery.

Diagnosing Amniotic Fluid Embolism

Amniotic fluid embolisms are a clinical diagnosis based on the presence of certain exam findings and the exclusion of other potential causes for those findings. [6] It should be suspected in pregnant or recently postpartum birthers who suddenly have heart failure, severe respiratory difficulty due to lack of oxygen, and/or seizures. An embolism is even more likely if these changes are followed by DIC.

Unfortunately, in many cases the diagnosis is made after the fact–once all the clinical data, including autopsy information when appropriate, have been collected.

Amniotic Fluid Embolism Treatment

Treatment for amniotic fluid embolism is mainly supportive, but it has become clear that early and aggressive management is critical to both fetal and maternal survival. [1,8] This requires an early diagnosis, prompt resuscitation efforts, and the delivery of the baby, including delivery via cesarean section to get the baby out as fast as possible. [1,2,8] 

There are several therapies available focused on stabilizing the birther and preventing the progression of the disorder. See our piece for a more detailed review.

Key Takeaways

Amniotic fluid embolisms are a difficult birth complication to predict, making them difficult to effectively prevent. As rare as this condition is, it is still one that birthers should be aware of due to its significant risks. Amniotic fluid embolisms have the potential to be fatal for both the birther and the baby, so immediate and aggressive medical intervention is critical to ensuring their survival. As alarming as this is, please know that the condition is rare; if you have any questions or concerns about AFE, talk with your OBGYN.

If you've already had an amniotic fluid embolism in the past or are currently recovering from one, it’s important that you speak with your doctor to plan for any future pregnancies. They will make sure that the measures needed to protect your health are in place before you get pregnant.