2 - 5 Indeed, the activation of the immune system and the coagulation cascade are closely intertwined in different physiologic and pathologic conditions. In summary, given similarities with findings observed in the vascular events typical of anaphylaxis and sepsis, immune responses affecting vascular homeostasis particular to pregnancy might play a major role in AFE. In support of this possibility, acute postpartum myometritis with invasion of leukocytes and mast cells, uterine atony, and postpartum hemorrhage, is frequently associated with AFE. 3 Alternatively, mast cells may massively degranulate, independent of classic antigen-IgE antibody anaphylaxis mechanisms. In support, complement C3a decreases in the blood, suggesting possible complement activation in AFE, possibly reflecting the access of fetal constituents to the maternal circulation. 2 The observation that pulmonary embolism does not have clinical features commonly found in AFE, such as coagulopathy, cardiovascular collapse, and neurologic symptoms, also suggests that a purely mechanical event is not sufficient to explain the pathogenesis of AFE.Īn immune-mediated theory involves the breakdown of the maternal-fetal barrier with exposure of fetal or trophoblastic material that prompts in individual pregnant women the generation of inflammatory mediators, leading to a severe acute response and subsequent AFE. However, the extent of the phenomenon varies, and it can also occur in patients without AFE. The invasion of amniotic, fetal, or trophoblastic components into the maternal circulation is a common feature.
The origin of AFE is not fully understood. The standardized classification may also facilitate distinction of common differential diagnoses, such as hemorrhagic, septic, or anaphylactic shock, anesthetic accident, or pulmonary thromboembolism. 2 This definition was recently developed for research purposes because in clinical practice, atypical variants of AFE that are missing some components may be occasionally diagnosed. This limitation was appropriately disclosed by the authors and does not diminish the study’s importance and generalizability.Īmniotic fluid embolism is a rare and serious pregnancy complication represented by unexpected cardiorespiratory arrest or hypotension, with respiratory compromise, hypoxia, or reduced oxygen saturation and disseminated intravascular coagulation occurring before significant hemorrhage and during labor, delivery, or immediately postpartum in absence of maternal hyperpyrexia. It may therefore include inaccuracies and lack of some covariates that could influence the interpretation of results. The main limitation is related to the retrospective design from a nationwide database for clinical administrative use and not specifically designed for research. Given the large sample size, the study would be not easily reproducible, making it even more valuable. This scientifically sound and clinically relevant study contributes significantly to expanding current knowledge on AFE. The classification tree model showed that the risk of AFE was 6.5% in the high-risk group with PAS associated with abruption and preterm birth, which decreased to 0.4% in women older than 40 years and 0.001% in low-risk cases (term vaginal deliveries). The mean AFE mortality in this study was 17.0%, increasing up to 45.0% when AFE was combined with other morbidities.
Moreover, the study showed the extent of the AFE association with other severe maternal morbidities (coagulopathy aOR, 25 cardiac arrest aOR, 25 and adult respiratory distress syndrome aOR, 11). Overall, 4% of patients with AFE presented with PAS. Placenta accreta spectrum showed a mean adjusted odds ratio (aOR) for AFE of 10.0 and a higher association for severe forms (accreta aOR, 7.6 increta/percreta aOR, 17.3). Among various variables, including maternal, pregnancy, and delivery features, the authors confirmed a significant association with known factors (of which the most significant were placenta abruption, advanced maternal age, and preterm birth) and revealed for the first time the impact of placenta accreta spectrum (PAS). The estimated incidence of AFE was 6 per 100 000 deliveries, with a slight yet significant increase during the study period. The study by Mazza and colleagues 1 assessed pregnancy characteristics, risk factors, and maternal mortality of amniotic fluid embolism (AFE), analyzing a sizeable cohort that encompasses the national US inpatient population during a 3-year period with almost 15 million deliveries and 880 cases of AFE.
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