**3. Incidence and risk factors**

#### **3.1 Incidence**

The true incidence of amniotic fluid embolism is unknown. Discrepancies in diagnosis as well as inconsistencies in reporting practices lead to a wide range of estimates. AFE incidence ranges between 1 in 8000 and 1 in 80,000 pregnancies [8, 11, 12]. In 2012, Knight et al. reviewed available data sources from Australia, Canada, the Netherlands, the United Kingdom, and the United States to investigate incidence rates and identify variations in methodology in diagnosis of AFE. Their analysis found a reported incidence of AFE ranging from 1.9 cases per 100,000 in the United Kingdom to 6.1 cases per 100,000 cases in Australia. Differences in the reported incidence were attributed to a lack of internationally accepted diagnostic criteria for nonfatal cases of AFE as well as variance in methodology.

**133**

*Amniotic Fluid Embolism*

**3.2 Risk factors**

reported [9, 13–16].

detect this association [2].

and cesarean delivery (OR 5.7, 95% CI 3.7–8.7) [16]. Maternal risk factors [1, 3, 5, 6, 8, 9, 11, 13–16]:

• Advanced maternal age, >35

• Multiparity

• Ethnic minority

Fetal risk factors [15, 16]:

• Multifetal gestation

• Diabetes

• Male fetus

• Fetal distress

• Polyhydramnios

• Intrauterine death

*DOI: http://dx.doi.org/10.5772/intechopen.85726*

Review of various data registries reveals a wide range of conflicting data regard-

Knight et al. in 2012 reviewed data sources on incidence of AFE in Australia, Canada, the Netherlands, the United Kingdom, and the United States. Where data was available, they also examined risk factors associated with AFE. There were only two associations that were consistent across all five countries: induction of labor and maternal age [2]. In the Netherlands the association with age was not statistically significant. This may be a result of the limited power of the study given that all reported cases occurred in women who were 29 years of age or older. The data from Canada showed an association between AFE and all methods of medical induction of labor, while in the United Kingdom, there was only a statistically significant association with induction of labor using vaginal prostaglandins [2]. In the United States, all methods of induction of labor showed an increased odds ratio; however, this was not statistically significant [2]. Increased odds of AFE associated with placental previa and placental abruption was also observed. In the United Kingdom there was a statistically significant association between cesarean section when the amniotic fluid embolism occurred after delivery. There was no association with forceps or vacuum delivery; however, only a small subset of women underwent an operative vaginal delivery, so there is limited power to

Another group of researchers who conducted a population-based cohort study on 3 million birth records in the United States from 1999 to 2003 found AFE was associated with maternal age greater than 35 (OR 2.2, 95% CI 1.5–2.1). However, they did not find that AFE was significantly associated with induction of labor. They also reported an association of placenta previa (OR 30.4, 95% CI 15.4–60.1)

ing identifiable risk factors for AFE. Historically, risk factors associated with AFE included situations where there was an increased likelihood of exchange of maternal and fetal components [1, 2, 13]. Events such as cesarean delivery, operative vaginal delivery, cervical trauma, placenta previa, and abruption were frequently
