Incidence, risk factors, and consequences of amniotic fluid embolism.

BACKGROUND: Amniotic fluid embolism (AFE) is a rare but serious cause of maternal mortality whose aetiology remains obscure. Previous population-based studies have reported associations with labour induction and caesarean delivery.

METHODS: We updated a previous analysis based on the US Nationwide Inpatient Sample from 1999 to 2008. We adapted a diagnostic validation algorithm to minimise false-positive diagnoses, along with statistical methods that account for the stratified random sampling design.

RESULTS: Of the 8 571 209 deliveries recorded in the database, 276 met our case definition of AFE, of which 62 (22.9% of the 274 with known vital status) were fatal. Significant associations with AFE were observed for medical induction {adjusted odds ratio [aOR] = 1.7 [95% confidence interval (CI) 1.2, 2.5]}, caesarean delivery [aOR = 15.0; 95% CI 9.4, 23.9], instrumental vaginal delivery [aOR = 6.6; 95% CI 4.0, 11.1], and cervical/uterine trauma [aOR = 7.4; 95% CI 3.6, 14.9]. AFE was associated with increases in risk of stillbirth, hysterectomy, maternal death, and prolonged maternal length of delivery hospital stay.

CONCLUSIONS: AFE remains an extremely serious obstetric complication with high risks of maternal and fetal mortality. The increased risks of AFE associated with labour induction and caesarean delivery have implications for elective use of these interventions.