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Drug-Induced Labor Carries Risk of Rare But Dangerous Complication

Amniotic-fluid embolism can prove fatal to mother, study says

FRIDAY, Oct. 20, 2006 (HealthDay News) -- Drug-induced labor nearly doubles the risk for a serious delivery complication that can cost the mother her life, a new study finds.

In light of the increased risk for this problem, called amniotic-fluid embolism, women and physicians should think twice about elective induction, though not necessarily about medically indicated induction, says the study in the Oct. 21 issue of The Lancet.

"There's very good evidence that a week or two after the due date, routine induction reduces the risk of stillbirth, so I would not say that that should change," said Dr. Michael Kramer, lead author of the study and scientific director of the Institute of Human Development and Child and Youth Health at the Canadian Institutes of Health in Ottawa, Ontario.

The real question is those inductions that occur as a matter of convenience, say, for example, the mother's obstetrician is going away or the in-laws are in town.

"This should at least be known by the women and the doctors who are making the decision," Kramer said.

Other experts, however, felt that the study findings were unlikely to change current practice.

"It's a rare, rare occurrence, and I don't think this is going to affect how people manage things at this point," said Dr. Abe Shahim, an obstetrician/gynecologist and attending physician at Lenox Hill Hospital in New York City.

And, the study authors themselves said that even though the number of women having induced labor has risen, there has been no commensurate rise in the rate of amniotic-fluid embolism. "That's my point," Shahim said. "It's so rare, it has no significant bearing on day-to-day practice."

An amniotic-fluid embolism is thought to arise when a simultaneous tear occurs in the fetal sac and in the vessels surrounding the uterus, allowing amniotic fluid to seep into the mother's circulatory system. Despite its rarity, the complication is one of the leading causes of maternal death in developed countries.

The new study marks the first time that anything has been identified as a risk factor for the condition. "The suspicion that induction of labor might be involved has been there for a couple of decades, but it has been unsubstantiated," Kramer said.

Because the complication is so rare, the investigators needed to study a very large population of women. Such a dataset was available in Canada, which keeps records of all hospital discharges in most provinces. Records include clinical diagnoses of conditions and of procedures like Caesarean sections and inductions that wouldn't be found on birth certificates.

In all, the database included information on more than 3 million hospital births in Canada from 1991 through 2002.

Of almost 3 million single births, there were 180 cases of amniotic-fluid embolism, 24 of them (13 percent) fatal. This translated into a total rate of six amniotic-fluid embolisms per 100,000 single-birth deliveries and a mortality rate of 0.8 per 100,000 deliveries.

The problem arose twice as often in women who had drug-induced labor versus those who did not. Other risk factors included maternal age of 35 or older, multiple pregnancy, Caesarean or vaginal forceps delivery, cervical laceration or uterine rupture, eclampsia and fetal distress.

The absolute risk remained small -- only four or five cases and one or two fatal cases per 100,000 women induced.

But with 4 million births each year in the United States, and induction rates approaching 20 percent, that could mean 30 to 40 cases each year in the U.S. alone, 10 to 15 of those fatal, the researchers said.

The relationship between induced labor and amniotic-fluid embolism is, so far, just an association, not one of cause-and-effect. But it's unlikely anything more concrete will turn up, according to the researchers.

"If there's something about the nature of that association that's not causal, that's going to be almost impossible to find out because the only way to know that for sure is a randomized trial which is almost impossible," Kramer said. "We would have to have hundreds of thousands if not millions of deliveries."

More information

The American Pregnancy Association has more on inducing labor.

SOURCES: Michael S. Kramer, M.D., scientific director, Institute of Human Development and Child and Youth Health, Canadian Institutes of Health Research, and professor of pediatrics and epidemiology and biostatistics, McGill University Faculty of Medicine, Montreal; Abe Shahim, M.D., attending physician, Lenox Hill Hospital, New York City; Oct. 21, 2006, The Lancet
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