Women who have their births drug-induced have nearly a two-fold increased risk of an amniotic-fluid embolism - a rare but serious delivery complication, according to an Article in this week's issue of The Lancet. The substantially raised risks should be a cause for concern, in view of the increasing tendency for clinicians to induce labour, and especially for routine induction at term or after term, state the authors.
An amniotic-fluid embolism arises when a simultaneous tear occurs in the fetal sac and in the vessels surrounding the uterus, allowing amniotic fluid to escape into the mother's circulatory system. Though this complication is rare it can be serious and even fatal; amniotic-fluid embolism is one of the leading causes of maternal mortality in developed countries. Little is currently known about the causes of the complication.
In the latest study, Michael Kramer (McGill University, Montreal, Canada) and colleagues investigated potential risk factors for amniotic-fluid embolism including labour induction. The researchers analysed data from over 3 million hospital births in Canada from 1991-2002. They found that of the 2 984 977 single births, there were 180 cases (24 fatal) of amniotic-fluid embolism, giving a total rate of 6 amniotic-fluid embolisms per 100 000 deliveries and a fatal rate of 0•8 per 100 000 deliveries. Amniotic-fluid embolism arose almost twice as frequently in women who had medical (drug) induction of labour as in those who did not; fatal cases were 3.5 times more frequent. The researchers also recorded raised rates of amniotic-fluid embolism in association with other complications such as diabetes and pre-eclampsia, and with increased maternal age and with caesarean, vacuum, and forceps deliveries.
The researchers emphasise that the absolute risk increase of amniotic-fluid embolism for women undergoing medical induction of labour is very small: four or five total cases and one or two fatal cases per 100 000 women induced. However, they state that with 4 million births per year and induction rates approaching 20% in the USA, the practice could be causing amniotic-fluid embolism in 30–40 women per year in USA alone (including 10–15 deaths).
The authors' conclude: "Our data support the longstanding, but previously unsubstantiated, suspicion that labour induction increases the risk of this rare but serious maternal complication. Although the small absolute risk of amniotic-fluid embolism is unlikely to affect the decision to induce labour in the presence of compelling clinical indications, women and physicians should be aware of this risk if the decision is elective."
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Contact: Professor Michael S Kramer, 2300 Tupper Street, Montreal, Quebec H3H 1P3, Canada. T) 1-514-412-4400 Ext 22687 firstname.lastname@example.org
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