From caution to certainty: hazards in the formation of evidence-based practice - a case study on evidence for an association between the use of uterine stimulant drugs and amniotic fluid embolism

Anaphylactoid Syndrome of Pregnancy

Anaphylactoid syndrome of pregnancy (ASP) is a widespread, proinflammatory, anaphylactic-like reaction that can occur when amniotic fluid enters the maternal blood circulation. ASP is characterized by four cardinal findings: respiratory distress, altered mental status, hypotension, and disseminated intravascular coagulation. ASP is commonly associated with maternal and neonatal mortality. Early recognition followed by prompt and aggressive treatment can improve survival rates and are among the most critical activities for nurses and other clinicians caring for women with ASP.

Amniotic-fluid embolism and medical induction of labour: a retrospective, population-based cohort study

BACKGROUND

Amniotic-fluid embolism is a rare, but serious and often fatal maternal complication of delivery, of which the cause is unknown. We undertook an epidemiological study to investigate the association between amniotic-fluid embolism and medical induction of labour.

METHODS

We used a population-based cohort of 3 million hospital deliveries in Canada between 1991 and 2002 to assess the associations between overall and fatal rates of amniotic-fluid embolism and medical and surgical induction, maternal age, fetal presentation, mode of delivery, and pregnancy and labour complications.

FINDINGS

Total rate of amniotic-fluid embolism was 14.8 per 100,000 multiple-birth deliveries and 6.0 per 100,000 singleton deliveries (odds ratio 2.5 [95% CI 0.9-6.2]). Of the 180 cases of amniotic-fluid embolism in women with singleton deliveries during the study period, 24 (13%) were fatal. We saw no significant temporal increase in occurrence of amniotic-fluid embolism for total or fatal cases. Medical induction of labour nearly doubled the risk of overall cases of amniotic-fluid embolism (adjusted odds ratio 1.8 [1.3-2.7]), and the association was stronger for fatal cases (crude odds ratio 3.5 [1.5-8.4]). Maternal age of 35 years or older, caesarean or instrumental vaginal delivery, polyhydramnios, cervical laceration or uterine rupture, placenta previa or abruption, eclampsia, and fetal distress were also associated with an increased risk.

INTERPRETATION

Medical induction of labour seems to increase the risk of amniotic-fluid embolism. Although the absolute excess risk is low, women and physicians should be aware of this risk when making decisions about elective labour induction.