Amniotic-fluid embolism is a rare complication of delivery, the cause of which is unknown. It remains one of the major causes of maternal deaths in developed countries. This population-based cohort study sought to clarify the association between amniotic-fluid embolism and medical induction of labor in a cohort of 3 million hospital deliveries taking place in several regions of Canada in the years 1991–2002.
Rates of amniotic-fluid embolism were 6.0 per 100,000 singleton deliveries and 14.8 per 100,000 multiple-birth deliveries, for an odds ratio (OR) of 2.5 (95% confidence interval [CI], 0.9–6.2). Only singleton births were analyzed further. Of 180 affected singleton births, 24 were followed by the mother's death, for a case-fatality rate of 13%. There was no apparent increase over time in amniotic-fluid embolism for either total cases or fatal cases. Medical induction of labor nearly doubled the risk of amniotic-fluid embolism; the adjusted OR was 1.8 (95% CI, 1.3–2.7). For fatal cases the crude OR was 3.5 (95% CI, 1.5–8.4). Other factors associated with an increased risk of amniotic-fluid embolism included a maternal age of 35 or above, cesarean delivery, instrumental vaginal delivery, polyhydramnios, cervical laceration, uterine rupture, placenta previa, placental abruption, eclampsia, and fetal distress. Advanced maternal age nearly doubled the risk, whereas young maternal age strongly protected against amniotic-fluid embolism. Forceps-assisted vaginal delivery carried a higher risk than did vacuum-assisted delivery. Even after adjusting for these risk factors and also for year of delivery, medical induction of labor nearly doubled the risk of amniotic-fluid embolism. Neither elderly primigravidity nor grand multiparity was a risk factor.
These findings indicate that inducing labor medically increases the risk of amniotic-fluid embolism. It is important for parturients and their physicians to be aware of this association, even if the small increase in absolute risk is unlikely to alter a decision to induce labor if appropriate clinical indications are present.