Amniotic fluid embolism: incidence, risk factors, and impact on perinatal outcome.

OBJECTIVE: To extend our previous work on AFE in Canada by including stricter criteria for case identification and by examining risks for stillbirth, neonatal mortality and serious maternal and neonatal morbidity.

DESIGN: Population-based cohort study.

SETTING: Canada.

POPULATION OR SAMPLE: In all, 4,508,462 hospital deliveries from fiscal year 1991/92 to 2008/09.

METHODS: To reduce false-positive diagnoses, we restricted our analysis to AFE cases with cardiac arrest, shock or severe hypertension, respiratory distress, mechanical ventilation, coma, seizure, or coagulation disorder. Linkage of maternal and neonatal records, available since 2001/02, enabled us to examine the effects of AFE on neonatal outcomes. Detailed demographic and clinical data facilitated control for a broad array of potential confounding variables.

MAIN OUTCOME MEASURES: Amniotic fluid embolism, in-hospital neonatal death, asphyxia, mechanical ventilation, bacterial sepsis, seizure, nonimmune haemolytic or traumatic jaundice and length of hospital stay.

RESULTS: A total of 292 AFE cases were identified, of which only 120 (40%) were confirmed after applying our additional diagnostic criteria, yielding an AFE incidence of 2.5 per 100,000 deliveries. Of the 120 confirmed cases, 33 (27%) were fatal. Significant modifiable risk factors included medical induction, caesarean delivery, instrumental vaginal delivery, and uterine or cervical trauma. Amniotic fluid embolism was associated with significantly increased risks of stillbirth and neonatal asphyxia, mechanical ventilation, sepsis, seizures and prolonged length of hospital stay.

CONCLUSIONS: Amniotic fluid embolism remains a rare but serious obstetric outcome, with several important modifiable risk factors and major implications for maternal, fetal and neonatal health.