In the past, diagnosis of ASP was commonly made at the time of autopsy when fetal squamous cells were detected in the maternal pulmonary circulation. In fact, in some countries, the case definition of ASP still includes pathological diagnosis of fetal squamous cells/debris in the maternal pulmonary circulation, despite clear evidence that this finding is non-diagnostic.2,4,6,8,9
We support the recommendation of the Society for Maternal-Fetal Medicine (SMFM) that ASP is a clinical diagnosis and often one of exclusion, involving elimination of other more common causes of maternal cardiovascular instability or coagulopathy. (Table 2).10 A multispecialty expert panel including representatives of the Society for Maternal-Fetal Medicine, the National Institutes of Health and the Centers for Disease Control have published a set of diagnostic criteria for AFE for use in development and evaluation of studies of AFE/ASP (Table 1).10 These criteria were developed to address the problem of a body of existing literature heavily populated with patients who did not actually have ASP. Such errors have contributed to confusion and misunderstanding regarding the nature of this condition, risk factors and prognosis.
Retrospective review of cases of suspected AFE/ASP by experts have found that up to 50% of cases coded as AFE/ASP have other more likely diagnoses, making use of population-based studies derived from administrative coding data particularly problematic.11 These criteria have been validated; while their use will reliably exclude women without ASP from research databases, they will also exclude a small number of women with atypical presentations of this condition.12
Prognosis and recurrence
Reported mortality from ASP/AFE has decreased significantly over the last several decades, in part due to recognition of the existence of less severe, atypical presentations. Recent reports suggest a survival rate of up to 80%.13 However, heavy contamination of administrative coding-based studies with patients who do not have this condition suggest caution in interpretation of such mortality data. In reports based on actual medical records review by experts in critical care obstetrics, both incidence of ASP and survival rates are generally lower.2,11 In women whose initial presentation includes cardiopulmonary arrest, prognosis remains poor. After recovery from hemodynamic derangements and coagulopathy, many patients will have acute lung injury/acute respiratory distress syndrome. Hypoxic brain injury may also be sustained due to the initial severe hypoperfusion and hypoxia. Echocardiography may reveal evidence of right ventricular overload and dilation, pulmonary artery hypertension, and contractile dysfunction of the left ventricle.14-16 Risk of recurrence with ASP is unknown, however, to date no recurrences have been reported. Given the apparent uncommon and unique interaction between patient and fetus-specific antigen involved in this condition, recurrence would not be expected with a different fetus.
When faced with sudden peripartum cardiopulmonary collapse or suspected ASP, the obstetrician’s initial role is to recognize the various possible etiologies. If ASP is suspected based on the triad of hypoxia, hypotension, and coagulopathy in addition to timing around time of delivery, the first step is to provide high-quality cardiopulmonary resuscitation (CPR) as indicated (Table 3).
Treatment is primarily supportive. An important concurrent step is to ask for help from team members including nursing, obstetrics partners or maternal-fetal medicine experts, anesthesia personnel, critical care personnel, and the blood bank. Left lateral uterine displacement, or in a potentially viable fetus (≥ 23 weeks’ gestation) delivery during resuscitation efforts may increase cardiac preload and improve the effectiveness of CPR by relieving inferior vena cava pressure caused by the gravid uterus. Intubation will likely be needed for ongoing respiratory support. Even prior to clinical signs of hemorrhage, we recommend notifying the blood bank and perhaps activating a massive transfusion protocol if suspicion for ASP is high as at least 80% of these women will develop DIC.4 Based on the presumed pathophysiology of ASP, a novel regimen of atropine, ondansetron and ketorolac has been proposed.17 Although survival with use of this regimen has been described and may reasonably be incorporated into standard treatment approaches for ASP, its actual efficacy is uncertain.
The Amniotic Fluid Embolism Foundation, a unique collaboration between private and academic institutions, has been established both to assist patients and families who have encountered ASP and to promote research efforts. Information regarding participation in an ongoing national registry of ASP cases is also available through the foundation website, at https://www.afesupport.org/.
Illustration by Alexandra Webber Baker, DNA Illustrations Inc. Click here to see more of her work.
The author reports no potential conflicts of interest with regard to this article.
- Chang J, Elam-Evans LD, Berg CJ, et al. Pregnancy-related mortality surveillance--United States, 1991--1999. MMWR Surveill Summ. 2003;52:1-8.
- Clark SL. Amniotic fluid embolism. Obstet Gynecol. 2014;123:337-48.
- Ecker JL, Solt K, Fitzsimons MG, MacGillivray TE. Case records of the Massachusetts General Hospital. Case 40-2012. A 43-year-old woman with cardiorespiratory arrest after a cesarean section. N Engl J Med. 2012;367:2528-36.
- Clark SL, Hankins GD, Dudley DA, Dildy GA, Porter TF. Amniotic fluid embolism: analysis of the national registry. Am J Obstet Gynecol. 1995;172:1158-67; discussion 67-9.
- Steiner PE, Luschbaugh CC. Maternal pulmonary embolism by amniotic fluid. JAMA. 1941;117:1245-51.
- Clark SL, Pavlova Z, Greenspoon J, Horenstein J, Phelan JP. Squamous cells in the maternal pulmonary circulation. Am J Obstet Gynecol. 1986;154:104-6.
- Funk M, Damron A, Bandi V, Aagaard K, Szigeti R, Clark S. Pulmonary vascular obstruction by squamous cells is not involved in amniotic fluid embolism. Am J Obstet Gynecol. 2018;218:460-1.
- Royal College of Obstetricians and Gynecologists. UK Obstetric Surveillance System Amniotic fluid embolism. Available at: https://www.npeu.ox.ac.uk/ukoss/current-surveillance/amf. Accessed May 23, 2018.
- Australasian Maternal Outcomes Surveillance System Amniotic fluid embolism. Available at: http://www.amoss.com.au/?q¼content/amniotic-fluid-embolism-afe. Accessed May 23, 2018.
- Society for Maternal-Fetal Medicine. Electronic address pso, Pacheco LD, Saade G, Hankins GD, Clark SL. Amniotic fluid embolism: diagnosis and management. Am J Obstet Gynecol. 2016;215:B16-24.
- Clark SL, Romero R, Dildy GA, et al. Proposed diagnostic criteria for the case definition of amniotic fluid embolism in research studies. Am J Obstet Gynecol. 2016;215:408-12.
- Stafford I, Moaddab A, Klassen M et al. Diagnostic precision of proposed criteria for research reporting of amniotic fluid embolism. Am J Obstet Gynecol. 2018;218: S122-123.
- Knight M, Tuffnell D, Brocklehurst P, Spark P, Kurinczuk JJ, System UKOS. Incidence and risk factors for amniotic-fluid embolism. Obstet Gynecol. 2010;115:910-7.
- McDonnell NJ, Chan BO, Frengley RW. Rapid reversal of critical haemodynamic compromise with nitric oxide in a parturient with amniotic fluid embolism. Int J Obstet Anesth. 2007;16:269-73.
- James CF, Feinglass NG, Menke DM, Grinton SF, Papadimos TJ. Massive amniotic fluid embolism: diagnosis aided by emergency transesophageal echocardiography. Int J Obstet Anesth. 2004;13:279-83.
- Evans S, Brown B, Mathieson M, Tay S. Survival after an amniotic fluid embolism following the use of sodium bicarbonate. BMJ Case Rep. 2014;2014.
- Rezai S, Hughes AC, Larsen TB, Fuller PN, Henderson CE. Atypical amniotic fluid embolism managed with a novel therapeutic regimen. Case Rep Obstet Gynecol. 2017; published online dec 21 2017.