Labor Induction Increases Risk of Rare Amniotic Fluid Emboli

From Reuters Health Information
David Douglas

May 7, 2010 — Labor induction, a multiple pregnancy, and cesarean delivery each increases the risk of rare but deadly amniotic fluid emboli, UK researchers report.

Older ethnic-minority women are also at higher risk, according to the article in the May Obstetrics & Gynecology.

"Induction of labor was associated with a population-attributable risk of 35% in our study, suggesting that, assuming causality, if induction of labor were no longer performed, 35% of cases of amniotic fluid embolism could be prevented," said lead author Dr. Marian Knight of the University of Oxford and colleagues.

Of course, they add, labor induction "clearly will continue, and amniotic fluid embolism remains a very rare complication" — but one to keep in mind when considering the risks and benefits of induction.

Using national UK Obstetric Surveillance System data from 2005 to 2009, the researchers found 60 confirmed cases among an estimate of more than 3 million maternities (for estimated incidence of 2.0 cases per 100,000 births).

They note that this rate, based on prospectively collected data, is lower than reported in retrospective studies from Canada and the U.S. (6.1 and 7.7 cases per 100,000 births, respectively).

After adjustment, amniotic-fluid embolism was significantly associated with induction of labor (odds ratio, 3.86) and multiple pregnancy (odds ratio 10.9). This risk was also higher in older, ethnic-minority women (odds ratio 9.85).

Regarding what she called "a possible increased risk of dying from amniotic fluid embolism amongst ethnic minority women," Dr. Knight speculated in email to Reuters Health that "reasons for this...may be related to underlying additional medical problems or access to care."

Cesarean delivery was associated with postnatal amniotic-fluid embolism (odds ratio 8.84).

The emboli occurred at a median gestation of 39 weeks, within a 6-hour range around delivery. All of the women had at least one cardinal sign of an embolism (shortness of breath, hypotension, hemorrhage, coagulopathy, and premonitory symptoms), and more than a quarter of them had at least four signs.

Fetal membranes ruptured at or before presentation in 92% of cases.

Twelve women died, giving a case fatality rate of 20%. These women were significantly more likely to be from ethnic-minority groups (odds ratio, 11.8).

Seven women received exchange transfusion or plasma exchange. All seven of these women survived, although there were too few of them to be able to infer that this treatment is more effective than other approaches. "These therapies should be regarded as an extension of supportive care and not as a substitute," the investigators said.

Outcomes were known for 37 neonates born to mothers with amniotic fluid embolism before or during delivery. Five of these babies died. The perinatal mortality rate was 135 per 1,000 total births.

"Occurrence of amniotic fluid embolism does appear to be associated with induction of labor and caesarean delivery and it is important therefore that both risks and benefits of labor induction and cesarean delivery are considered by clinicians on an individual basis for all women," Dr. Knight said.

"We have no indication from this study that the occurrence has become more frequent in the UK," she said.

Obstet Gynecol. 2010;115:910-917. Abstract

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