Incidence and Risk Factors for Amniotic-Fluid Embolism

OBJECTIVE: To estimate the incidence of amniotic-fluid embolism and to describe risk factors, management, and outcomes. METHODS: Through a population-based cohort study and nested case-control analysis, using the UK Obstetric Surveillance System, we identified 60 women in the United Kingdom who had an amniotic-fluid embolism between February 2005 and February 2009 and 1,227 women for the control group. We investigated the potential factors underlying amniotic-fluid embolism using an exploratory logistic regression analysis to estimate odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: Sixty cases of amniotic-fluid embolism were reported, an estimated incidence of 2.0 per 100,000 deliveries (95% CI 1.5-2.5). Amniotic-fluid embolism occurrence was significantly associated with induction of labor (adjusted OR 3.86, 95% CI 2.04-7.31) and multiple pregnancy (adjusted OR 10.9, 95% CI 2.81-42.7); an increased risk also was noted in older, ethnic-minority women (adjusted OR 9.85, 95% CI 3.57-27.2). Cesarean delivery was associated with postnatal amniotic-fluid embolism (adjusted OR 8.84, 95% CI 3.70-21.1). Twelve women died (case fatality 20%, 95% CI 11-32%); 5 of 37 newborns of women with antenatal amniotic-fluid embolism died (perinatal mortality 135 per 1,000 total births, 95% CI 45-288). Women who died were significantly more likely to be from ethnic-minority groups (adjusted OR 11.8, 95% CI 1.40-99.5). CONCLUSION: High-quality supportive care can result in good maternal outcomes after amniotic-fluid embolism. Clinicians should consider both the risks and benefits of induction and cesarean delivery because more restricted use may result in a decrease in the number of women suffering a potentially fatal amniotic-fluid embolism. The observed increased risk of fatality in ethnic-minority women may be associated with differences in underlying medical conditions or access to care, and clinicians should that ensure appropriate services are provided to minimize this risk.