Amniotic Fluid Embolism and Uterine Atony- Two Case Reports and Literature Review

Both of aforementioned cases highlight the importance of early recognition of amniotic fluid embolism as a potential cause of uterine atony and postpartum bleeding, as well as importance of aggressive approach and multidisciplinary team cooperation in order to improve both neonatal and maternal outcomes.

Amniotic fluid embolism is a rare condition, but exact incidence is difficult to estimate, because many studies may overestimate number of AFE cases. However, it is believed that it ranges from 1.9 to 6.1 cases per 100,000 deliveries^4-6 with high mortality that ranges from 20 to 60 percent³. Systematic review from Frati et al. determined that incidence of AFE is 5.5 cases per 100,000 deliveries with 24.8 % mortality rate⁷.

Risk factors associated with the development of amniotic fluid embolism and subsequently uterine atony include maternal age over 35 years, multiparity, induction of labor, placental abnormalities, preeclampsia and eclampsia. cesarean delivery or instrumental vaginal delivery, fetal distress, fetal death, and male fetus^3,5,8-10. Both patients that we presented can be associated with these risk factors: both were over 35 years old and were multigravidas, and both labors were induced for different reasons. Even though AFE is a rare condition, it is important to recognize parturient with increased risk of development. The diagnosis is a challenge for clinicians, due to often non-specific symptoms, and definitive diagnosis is often made after pathohistological examination or in the absence of other explanations for said symptoms. Some studies suggested Zinc protorphyrin (ZnCP-1) from fetal meconium and urine, Sialosyl TN (STN), interleukin-6, and tryptase as markers which could help diagnose AFE⁷.

Because of severity and diagnostic complexity of this condition, Society for Maternal-Fetal Medicine (SMFM) and Amniotic Fluid Embolism Foundation proposed a definition of AFE based on the presence of four diagnostic criteria¹¹:

1. Sudden onset of cardiorespiratory arrest or hypotension (defined as systolic blood pressure <90 mmHg) with evidence of respiratory compromise such as dyspnea, cyanosis, or peripheral oxygen saturation <90 per cent.
2. Disseminated intravascular coagulation (DIC)based on the International Society on Thrombosis and Haemostasis (ISTH) scoring system, adapted for pregnancy¹²: platelet count: >100,000/mL (0 points), <100,000/mL (1 point), <50,000 (2 points); prolonged prothrombin time or international normalized ratio (INR) <25 percent increase (0 points), 25 to 50 percent increase (1 point), >50 percent increase (2 points); and fibrinogen level >200 mg/dL (0 points), <200 mg/dL (1 point). Score of 3 or greater is strong indicator for overt DIC.
3. Clinical onset of symptoms during labor or within 30 minutes of delivery of placenta.
4. Absence of fever of (≥38°C) during labor.

All of the aforementioned criteria must be present.

The pathogenesis of AFE is not yet fully understood. Two main theories have been proposed to explain the pathogenesis of the disease¹³. First is mechanical theory which attributes AFE to a pulmonal mechanical embolism caused by components in amniotic fluid (meconium, mucus, sebum, lanugo). This concept was first introduced in 1941 by Steiner and Lushbaug¹⁴. The second theory is the immune-mediated theory, presented in 1995 by Clark et al.¹⁵. This theory suggests that AFE is more similar to an anaphylaxis or septic shock-like response, driven by complement activation.  It is currently believed that discontinuity of maternal-fetal interface can lead to the entry of amniotic fluid into the maternal systemic circulation, which can lead to activation of immunological response and release of vasoactive and procoagulant substances^16,17. This leads to elevation of pulmonary pressure and, subsequently, pressure in right ventricle, followed by left ventricle and systemic hypotension. The result of this sequence is cardiogenic pulmonary edema and hypoxemic respiratory failure^2,15.

Amniotic fluid embolism can be divided into two types, based on clinical presentation: typical and atypical. Typical type presents into three phases: initial respiratory and circulatory distress, followed by coagulation disorders and progression to acute renal failure and acute respiratory distress syndrome (ARDS), followed by cardiopulmonary collapse. Atypical type presents without cardiopulmonary collapse and first symptom is disseminated intravascular coagulopathy (DIC) type involving uterine atony, massive hemorrhage and rapid progression of coagulopathy⁸.

Once AFE is diagnosed or suspected, treatment must be aggressive and include multidisciplinary approach between obstetrician, anesthesiologist, midwife and other team members.

In cases of cardiorespiratory arrest, cardiopulmonary resuscitation following Advanced Cardiac Life Support protocol for obstetric patients should be started. Furthermore, control of the hemorrhage and reversion of coagulopathy should be obtained, activation of massive transfusion protocol, and delivering the fetus if incident happens before the labor.