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CLEVELAND, July 21 -- Misoprostol should not be used for inducing labor in women with a history of uterine surgery or a prior cesarean delivery, according to new guidelines issued by the American College of Obstetricians and Gynecologists (ACOG).

Use of misoprostol in those women "has been associated with an increase in uterine rupture," the guidelines state.

The practice of inducing labor has become more common. More than 22% of pregnant women undergo labor induction, ACOG says, and the overall rate doubled from 1999 to 2006.

At the same time, there have been a number of reports linking the induction of labor with increased risk of adverse events including uterine rupture and meconium-stained amniotic fluid.

One of the areas of controversy is dosing of misoprostol.

The new guidelines include seven recommendations based on "good and consistent scientific evidence" -- considered the highest evidence level -- including one that sanctions 25 mcg of misoprostol as "the initial dose for cervical ripening and labor induction." The recommended frequency is "not more than every 3-6 hours."

ACOG said that the data on the safety of high-dose misoprostol (50 mcg every six hours) were "limited or inconsistent," making its recommendation on high-dose misoprostol an evidence level "B" recommendation.

High-dose misoprostol, the guideline states, "may be appropriate in some situations, although higher doses are associated with an increased risk of complications, including uterine tachysytole with [fetal heart rate] decelerations."

In addition to the cautions on misoprostol in high risk populations and concerns about dosing of the drug, the guidelines include these "A" level recommendations:

• Prostaglandin E analogues are effective for cervical ripening and inducing labor.
• Low- or high-dose oxytocin regimens are appropriate for women in whom induction of labor is indicated.
• Before 28 weeks of gestation, vaginal misoprostol appears to be the most efficient method of labor induction regardless of Bishop score, although high-dose oxytocin infusion is also an acceptable choice.
• Intravaginal prostaglandin E₂ for induction of labor in women with premature rupture of membranes appears to be safe and effective.
• The Foley catheter is a reasonable and effective alternative for cervical ripening and inducing labor.

ACOG also states that the assessment of "gestational age and consideration of any potential risks to the mother or fetus are of paramount importance for appropriate evaluation and counseling before initiating cervical ripening or labor induction."

Gestational age should be confirmed by ultrasound measurement, documented 30-week fetal heart tones by Doppler ultrasonography, or confirmation that it has been 36 weeks since a positive serum or urine human chorionic gonadotropin pregnancy test result.

The recommendation writers also reviewed the use of methods for induction of labor with intrauterine fetal demise in the late second or third trimester.

Based on limited data, they wrote, "the use of misoprostol between 24 to 28 weeks of gestation also appears to be safe and effective. Before 28 weeks of gestation, vaginal misoprostol appears to be the most efficient method of labor. After 28 weeks of gestation, induction of labor should be managed according to usual obstetric protocols."

They recommend against cesarean delivery for fetal demise, noting it "should be reserved for unusual circumstances because it is associated with potential maternal morbidity without any fetal benefit."

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