Amniotic Fluid Embolism

Amniotic fluid embolism (AFE) is a critical obstetric emergency marked by sudden cardiorespiratory collapse and disseminated intravascular coagulation (DIC). Often referred to as the anaphylactoid syndrome of pregnancy, AFE is distinct from a direct embolism or the presence of amniotic fluid itself. The global occurrence of AFE ranges from 1 in 8000 to 1 in 80,000 deliveries, though the exact incidence remains unclear due to diagnostic and reporting inaccuracies.  In the United States, AFE ranks as the second leading cause of peripartum maternal death and the primary cause of peripartum cardiac arrest. Its presentation is abrupt, typically involving sudden cardiorespiratory collapse, altered mental status, and subsequent severe coagulopathy. Survivors often contend with serious cardiac, renal, neurologic, and pulmonary dysfunction. In the United States, AFE affects 2.2 to 7.7 per 100,000 deliveries, contributing to 7.5% of maternal deaths. In developing countries, the mortality rate ranges from 1.8 to 5.9 per 100,000 deliveries, compared to 0.5 to 1.7 per 100,000 deliveries in developed countries. The initial description of AFE dates back to 1941 when Steiner and Luschbaugh noted fetal cells in the maternal pulmonary circulation of women who died during labor. Data from the National Amniotic Fluid Embolism Registry indicates that the condition shares similarities with anaphylaxis rather than a typical embolism. Notably, fetal tissue or amniotic fluid components are not consistently detected in women displaying signs and symptoms of AFE. Traditionally, AFE diagnosis occurred postmortem, relying on the presence of fetal squamous cells in the maternal pulmonary artery blood. However, as fetal squamous cells are also found in the circulation of laboring women who do not develop AFE, the diagnosis is exclusionary and based on clinical presentation after ruling out other causes of hemodynamic instability.