Amniotic Fluid Embolism

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Amniotic fluid embolism (AFE) is a severe, life-threatening complication of pregnancy. Since cases that are not fatal are not always reported, and since the diagnosis is not always accurate, it is not clear exactly how often AFE occurs. However, the estimated incidence of AFE ranges from 1 per 8,000 to 1 per 80,000 deliveries. Women above age 35 and African American women have an elevated risk of developing AFE. You are also at increased risk if you have a multiple pregnancy, if the fetus dies, if you undergo surgical and other operative procedures for delivery, experience problems with the placenta, injuries, tears in the uterus or cervix, or if you suffer from a severed complication called eclampsia.

The amniotic fluid is a clear, pale to yellow fluid that fills the amniotic sac that contains, supports, and protects the fetus. The amniotic fluid lubricates the fetus, for instance, thereby protecting anatomic parts that stick out, particularly the distal extremities (fingers and toes), which otherwise can become webbed; webbing is one possible result of oligohydramnios, a condition in which there is an inadequate volume of amniotic fluid. The amniotic fluid also supports and lubricates the umbilical cord, thus preventing cord compression. The fluid is also extremely useful for sampling to obtain diagnostic information related to infections, genetic information, and lung maturity. Sampling of amniotic fluid by way of a needle is called amniocentesis.

The “E” part of AFE stands for embolism. The name AFE is rather misleading, since we think of embolism as a mass, so you may be thinking that the problem involves a particle consisting of amniotic fluid entering the bloodstream due to an injury of the amniotic sac and traveling through the blood until it obstructs a blood vessel. AFE is actually a reaction similar to anaphylaxis, a life-threatening reaction throughout the body set-off by an allergen. In the case of AFE, a reaction with features similar to anaphylaxis is triggered by the presence of amniotic fluid and fetal debris, such as cells or hair, in the pulmonary circulation of a pregnant woman. Thus, AFE does involve amniotic fluid escaping into the bloodstream, but the problem is not obstruction of a vessel initially, but the body’s reaction.

Whereas anaphylaxis is a severe kind of allergic reaction that a person may have in response to a particular drug or food, AFE has some things in common with pulmonary embolism (PE) in that the causative material reaches the lungs, but also with anaphylaxis in the response that develops in the affected person.  A woman suffering from AFE will have difficulty breathing, cyanosis (bluish skin, due to inadequate levels of oxygen), and a sudden, severe drop in blood pressure (below 90/60 mm Hg).

No particular test can reveal for certain whether there is an AFE. Thus, AFE is diagnosed based on the obstetrician, or other physicians, having a high level of suspicion, based on a combination of results from the physical examination and a battery of tests that can help rule out other conditions. Such tests include measurements of oxygen saturation in the blood, calcium, magnesium, and other chemicals in the blood, a complete blood count (CBC), blood clotting tests, electrocardiography (ECG), echocardiography. While performing the various tests, physicians need to rule out other life-threatening conditions that look a lot like AFE, such as a PE, an anaphylactic reaction to a drug, cardiomyopathy and cardiac arrhythmia (problems with the heartbeat), myocardial infarction (heart muscle tissue dies, due to cut-off of blood supply to some part of the heart muscle), aortic dissection (tearing in the main artery leading from the heart), sepsis (infection throughout the body), reaction to a transfusion, hemorrhage (severe bleeding), and various seizure conditions.

If a woman is suffering from an AFE, her blood pressure, heartbeat, and breathing must be stabilized immediately. If her heart stops pumping blood and she looses consciousness, then, after she is resuscitated, she must be put into hypothermia, lowered body temperature, in order to protect her brain. Through all of this, the fetus is in danger and makes treatment of the mother more difficult. A cesarean section may be needed. During resuscitation, the uterus may need to be moved around to keep blood flowing to the fetus.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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