Michael D. Benson

Michael D. Benson

Northwestern University, USA

Title: Amniotic fluid embolism: The known and not known


Michael Benson has been researching Amniotic Fluid Embolism, one of the leading causes of maternal mortality in developed nations, for the past two decades. His data suggests that Complement activation might have a role to play although he has also demonstrated that complement activation takes place during normal parturition. Author of three medical textbooks, Doctor Benson has published more than two dozen papers in the peerreviewed literature and has taught medical students at Northwestern for over 25 years.


Amniotic Fluid Embolism was fi rst recognized in 1926, in a Brazilian journal case report, on the basis of large amounts of fetal material in the maternal pulmonary vasculature at autopsy. Th e fi rst English language appeared in 1941 and consisted of 8 patients dying suddenly in which, once again, fetal material was seen in the pulmonary vasculature. A control group of 34 pregnant women dying of other recognized causes did not have fetal material in their lungs. Th e incidence of recognized, serious illness is on the order of 2 to 8 per 100,000 with a mortality rate ranging from 16 to 35%. Th e diagnosis rests largely on one or more of four clinical signs: circulatory collapse, respiratory distress, coagulopathy, and seizures/coma. Th e only confi rmatory laboratory test remains autopsy fi ndings although serum tests for fetal antigen, insulin-like growth factor binding protein-1 and complement are currently being investigated. One of the paradoxes of diagnosis is that fetal material in the pulmonary circulation at autopsy is specifi c for AFE, while the same fi nding in the living is not. Th e mechanism of disease remains uncertain although the best available evidence suggests that complement activation might have a role. In contrast, mast cell degranulation probably is not a mechanism so AFE is not an anaphylaxis or anaphylactoid reaction as has been occasionally suggested. Perhaps the greatest unknown is not why 1 in 50,000 pregnant women develop what appears to be an immune response to their fetus but rather why the other 49,999 do not?

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