Comparison of different sources of incidence data for amniotic fluid embolism
Amniotic fluid embolism (AFE) is a rare, but severe complication of pregnancy. A recent systematic review highlighted apparent differences in the incidence of with studies estimating the incidence of AFE to be more than three times higher in North America than Europe. The aim of this study was to examine population-based regional or national data within two North American countries, two European countries and a high resource country from a different region (Australia) in order to investigate incidence, risk factors and outcomes of AFE and to investigate whether any variation identified could be ascribed to methodological differences between the sources of data.
We reviewed available data sources on the incidence of AFE in Australia, Canada, the Netherlands, the United Kingdom and the USA. Where information was available, the risk factors and outcomes of AFE were examined.
The reported incidence of AFE ranged from 2.1 cases per 100 000 maternities (UK) to 6.1 per 100 000 maternities (Australia) (Table 2). There was a clear distinction between rates estimated using different methodologies. The lowest estimated incidence rates were obtained through validated case identification (range 2.1-2.4 cases per 100 000 maternities); rates obtained from retrospective analysis of population discharge databases were significantly higher (range 5.5-6.1 per 100 000 admissions with delivery diagnosis). There were no clear differences in mortality or case fatality rates. The only factor consistently associated with AFE across all five countries was older maternal age.
AFE incidence estimates should only be compared across studies using similar methodology. Recommended approaches are either population-based database studies with additional case validation, or bespoke data.
Comparisons of AFE incidence between and within countries would be facilitated by development of an agreed case definition and an agreed set of validation criteria for studies conducted using population-based databases.
Groups conducting detailed population-based studies on AFE should develop an agreed strategy to allow combined analysis of data obtained using consistent methodologies in order to inform the development of preventive strategies.
Future specific studies on AFE should aim, where possible, to collect information on management and longer-term outcomes for both mothers and infants in order to guide best practice, counselling and service planning.