- Amniotic fluid embolism is a leading cause of maternal mortality in developed countries.
- It presents with maternal collapse or seizures, or occasionally fetal distress.
- Resuscitation must be prompt and multidisciplinary, including delivery if necessary.
- There is no specific therapy except intensive support with transfusion.
- Mortality may not be as high as previously thought, since milder cases do occur.
A mniotic fluid embolism (AFE) is a dramatic and perplexing condition. Within moments of the appearance of symptoms, a gravida’s life is at stake, and both maternal and fetal deterioration are rapid. Further, because the diagnosis isn’t always clear, the hospital team must rule out other possible etiologies while trying to prevent respiratory arrest and hemorrhage. The relative rarity of AFE adds to the difficulty of deciphering its pathophysiology. That rarity, coupled with the complexity of management, may explain why AFE remains a leading cause of maternal death. In the United Kingdom over the past 15 years, AFE has been responsible for 8.4% of maternal deaths. In the United States and Australia, it has been associated with 7.5% to 10% of these deaths.1-3
Fortunately, a gloomy prognosis may no longer be inevitable. Over the past 20 years or so, mortality rates for AFE appear to have dropped. Still, when this condition presents, immediate action is vital if there’s any hope of saving mother and fetus. Here, I present clinical features that may signal an AFE and describe various management strategies outlined in the literature.
Declining mortality rates
A 1979 review suggested a mortality rate of 86% for women suffering an AFE. But in a retrospective look at the 1995 US National Amniotic Fluid Embolus Registry, researchers noted a mortality rate of 61%4,5 (though only 7% to 15% of all the women survived neurologically intact5). Other recent surveys report even lower mortality rates: under 30% (TABLE).3-6
The changing mortality rate is probably a result of 2 factors: better intensive care and a recognition that “milder” cases do occur. For example, as Benson notes, “the mere fact of survival” was generally considered “proof that a given individual did not have an amniotic fluid embolism.”7 Benson proposes a new clinical definition of AFE that would apply “to patients who survive as well as to those who die.”7 Milder cases tend to present with less dramatic collapse and often only transient hemodynamic change, whereas severe cases are characterized by collapse with cardiac arrest.
Amniotic fluid embolism-related mortality and morbidity: selected series
|SERIES||SITE||YEAR||NUMBER OF CASES||MORTALITY||OTHER MORBIDITY||INFANTS*|
|US registry (Clark)5||United States||Published 1995 (1988-1993)||46||61%||Only 15% neurologically intact||22/28 survived, 11 (50%) neurologically intact|
|Burrows and Khoo3||Brisbane, Australia||Published 1995 (1984-1993)||9||22%||2/9 had hysterectomy; 1 long-term disability||8/11 survived (2 sets of twins)|
|Gilbert and Danielsen6||California||Published 1999 (1994-1995)||57||28%||5/39 survivors needed “extra arrangements” on discharge†||95% survived; 72% normal discharge|
|UK registry (D.J.T., unpublished data)||United Kingdom||1997-2000||25||16%||4/21 survivors and 1 of 4 women who died had hysterectomy; 1 surviving woman had internal iliac ligation and liver hematoma; 2 women had renal failure and recovered; 1 woman had subglottic stenosis||3 perinatal deaths; 5/15 survivors severely acidotic|
|*From cases occurring before or at delivery only.|
|† The authors did not specify what these “extra arrangements” were.|
The pathophysiology of AFE is poorly understood. Amniotic fluid and fetal cells enter the maternal circulation, leading to sudden maternal or fetal deterioration—the hallmark clinical features of AFE.
In the United States, Clark established clinical criteria for AFE for the national registry; these criteria have been followed in the UK since 1997 in an effort to develop a registry of cases there.5,8 The criteria are:
- acute hypotension or cardiac arrest
- acute hypoxia (dyspnea, cyanosis, or respiratory arrest)
- coagulopathy (laboratory evidence of intravascular coagulation or severe hemorrhage)
- onset of all of the above during labor or within 30 minutes of delivery
- no other clinical conditions or potential explanations for the symptoms and signs
Typically, AFE presents with a cluster of features. This becomes clear when a larger series of cases is considered. In early series reporting a high mortality rate, such as the Morgan series, almost all women presented with cardiorespiratory collapse.4 Other signs and symptoms were breathlessness, hypotension, collapse (e.g., hypovolemic), and seizures. Fetal signs and symptoms did not figure in the Morgan series, but in 17% of the US series the abnormal fetal-heart-rate (FHR) pattern was bradycardia.5 In the UK series, 9 cases (36%) presented with abnormal FHR patterns, though not all had bradycardia (D.J.T., unpublished data). Coagulopathy and bleeding were uncommon presenting features in all 3 series, occurring at a rate of 12% in Morgan’s series, 0% in the US series, and 4% in the UK series. Coagulopathy and massive hemorrhage seem to be features that develop later. Often the coagulopathy is present shortly after presentation—and can be detected if looked for—but becomes clinically apparent only with time.