Low-Dose Oral and Vaginal Misoprostol for Cervical Ripening and Labor Induction
Abstract & Commentary
Synopsis: A 50-mcg dose of oral misoprostol is somewhat less effective than a 25-mcg dose of intravaginal misoprostol given every four hours for cervical ripening.
Source: Wing DA, et al. Am J Obstet Gynecol 1999; 180:1155-1160.
Many physicians are interested in oral misoprostol for cervical ripening and the induction of labor. Wing and colleagues from the University of Southern California randomized 220 women with medical or obstetric indications for labor induction to either 50 mcg of oral misoprostol or 25 mcg of intravaginal misoprostol every four hours. At enrollment, all subjects had a Bishop score less than 5. After 24 hours, the misoprostol was stopped. Those women with a Bishop score more than 7 began induction of labor with oxytocin. When subjects began active labor, they received routine intrapartum management, including oxytocin augmentation if needed, without regard to treatment group. The primary outcome measure was successful labor induction, defined here as vaginal delivery occurring within 24 hours after that start of induction.
Of the orally treated women, 30.9% had successful labor inductions, compared with 47.3% of vaginally treated women, a statistically significant difference (P = 0.01). The oral treatment group required a mean of 29.6 hours to deliver, while the vaginal treatment group required 25.4 hours (P = 0.03). The oral misoprostol group required a mean of 3.3 doses, the vaginal group 2.3 doses (P < 0.0001). Approximately 75.4% of the oral group required oxytocin, compared with 59.1% of the vaginal misoprostol group (P = 0.01). There were no significant differences in rates of uterine tachysystole, hyperstimulation, chorioamnionitis, neonatal outcomes, or cesarean deliveries between the two groups.
Comment by Elizabeth Morrison, MD, MSed
Misoprostol is an effective, safe, and inexpensive choice for cervical ripening and labor induction. Oral administration will allow outpatient cervical ripening, an attractive and cost-saving option for patients, physicians, and health systems. Recent research has focused on determining the best dose for oral misoprostol.
Oral misoprostol fans will be somewhat disappointed with the results of the study by Wing et al. For all out- come measures, low-dose oral misoprostol was signifi- cantly less effective than intravaginal misoprostol for ripening the cervix and inducing labor, although both the oral and vaginal doses appeared quite safe, and both allowed labor induction within a mean of 30 hours.
Several points should be taken into account when interpreting the results of this study. Subjects included women with varying gestational ages, less than 10% of the subjects were postdates. Women with hypertension and diabetes mellitus made up one-quarter of the study population, and their concomitant medical problems might have caused them to react differently to the misoprostol. Since the study medications were discontinued after 24 hours, it was not possible to determine whether the oral misoprostol might have had a stronger effect if given less frequently but, as other studies are exploring, for a longer treatment period.
These caveats aside, the study by Wing et al continues to support the idea that a 50-mcg oral misoprostol dose may be less effective than one would desire for cervical ripening at or near term. The answer may ultimately lie in using a higher dose of oral misoprostol with a less fre- quent dosing interval. Other investigators have found that a 100-mcg dose of oral misoprostol is as safe and effec- tive as the same dose given intravaginally.1 Oral doses of
200 mcg have also been studied,2 but tend to cause unacceptably high rates of uterine hyperstimulation.
It will be fascinating to see the results of ongoing and future studies of 100-mcg, 50-mcg, and even 25-mcg oral doses of misoprostol for cervical ripening. We also need to know how various oral misoprostol doses compare with placebo. When these issues are resolved, many of us hope to be able to offer appropriately-selected women the option of oral misoprostol for cervical ripening and labor induction. Although Wing et al did not find a 50-mcg dose given every four hours to be as effective as they had hoped, another dosing regimen may be found that is more effective in future studies.
References
1. Toppozada MK, et al. Int J Gynaecol Obstet 1997;56: 135-139.
2. Adair CD, et al. Obstet Gynecol 1998;92:810-813.
In the study of oral vs. vaginal misoprostol for "cervical ripening" and labor induction by Wing et al, significant differences between the oral and vaginal treatment groups were found for which one of the following outcomes?
a. Uterine hyperstimulation
b. Neonatal Apgar scores
c. Rates of cesarean delivery
d Rates of labor induction within 24 hours
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