Incidence and Risk Factors for Amniotic-Fluid Embolism

Abstract

Since 2005, a prospective surveillance of amniotic fluid embolism in the United Kingdom has been conducted with the UK Obstetric Surveillance System by using routine monthly mailings. The aim of this population-based cohort study was to estimate the incidence of amniotic fluid embolism and to investigate risk factors, management, case fatality, and other outcomes. Between 2005 and 2009, nested case-control analysis using the UK Obstetric Surveillance System identified 60 women who had amniotic fluid embolism. The control group consisted of women who were delivering in the same hospital immediately before the study group cases (2 per case). Potential factors underlying amniotic fluid embolism were investigated using an exploratory logistic regression analysis. During the 4-year study, the 60 confirmed cases of amniotic fluid embolism identified among an estimated 3,049,100 maternities represent an estimated incidence of 2.0 per 100,000 deliveries (95% confidence interval [CI], 1.5-2.5). The occurrence of amniotic fluid embolism was significantly associated with induction of labor (adjusted odds ratio [aOR], 3.86; 95% CI, 2.04-7.31) and multiple pregnancy (aOR, 10.9; 95% CI, 2.81-42.7). Increased risk was also found among ethnic minority women older than 35 years (aOR, 9.85; 95% CI, 3.57-27.2). Postnatal amniotic fluid embolism was associated with cesarean delivery (aOR, 8.84; 95% CI: 3.70-21.1). Of these, 12 women died, which represents a case fatality rate of 20% (95% CI, 11%-32%). There were 5 newborn deaths among the 37 neonates born to mothers who had antenatal amniotic fluid embolism, giving a perinatal mortality rate of 135 per 1000 total births (95% CI, 45-288). Women who died were much more likely to be from ethnic minority groups (aOR, 11.8; 95% CI, 1.40-99.5). These findings show that the risk of amniotic fluid embolism was significantly increased by induction of labor and multiple pregnancies and among ethnic minority women older than 35 years. The investigators postulated that the higher incidence of maternal morbidity and deaths among ethnic minority women may be because of the differences in underlying medical conditions or access to care.