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Using oral misoprostol to induce labor in a predominantly overweight population of pregnant women was associated with a higher portion of cesarean deliveries than vaginal misoprostol, according to a retrospective single-center study.

A higher proportion of women that received 50 micrograms of oral misoprostol for induction of labor progressed to cesarean delivery than women who received 25 micrograms of vaginal misoprostol (32% vs 21%, P=0.04), reported Roxane C. Handal-Orefice, MD, of Columbia University in New York City, and colleagues, writing in .

The authors stated that while a 2014 review found vaginal misoprostol to be less effective than oral misoprostol, this research is limited by its analysis of different doses of the medication. It was also noted that previous research has not sufficiently assessed BMI.

Moreover, recent results of the , which found decreased risk of cesarean delivery following induction of labor among nulliparous women versus expectant management, means that "induction rates will likely continue to increase," the authors said.

According to Handal-Orefice and colleagues, this study provides an analysis of the safest recommended dose of vaginal misoprostol compared with a commonly used dose of oral misoprostol to better evaluate the effectiveness and safety of the orally administered medication "in a predominantly overweight population."

Researchers examined data from Boston University Medical Center, after the facility began following a new protocol to administer oral versus vaginal misoprostol. They compared outcomes of women that received vaginal misoprostol from 2013 to 2014 with women that received oral misoprostol from 2014 to 2015. During each time period, oral or vaginal misoprostol were used exclusively for cervical ripening, the authors said.

This was a retrospective study, so to limit selection bias, the first 138 individuals presenting for induction during each time period who met study criteria were included, the authors said.

Baseline characteristics between both groups were similar. Of the 276 women, 72% were either black or Hispanic. The mean age of all participants was around 29-30. Around 57% of participants in the vaginal group and 64% in the oral group were nulliparous. The cohort was primarily considered overweight or obese, with a median BMI of 31.7 (28.2-36.8).

The adjusted odds of cesarean delivery were higher with the use of oral misoprostol (aOR 2.01, 95% CI 1.07-3.76), the authors wrote. This result persisted in women who had never given birth, with more frequent cesarean deliveries occurring in the oral misoprostol group (41%) than in the vaginal misoprostol group (28%).

Among the women that did progress to vaginal delivery, those in the oral misoprostol group had longer median time to delivery in the adjusted censored analysis than the vaginal misoprostol group (41 hours vs 31 hours, respectively, P=0.01). Tachysystole, or excessive uterine contractions, was more common in women that received vaginal misoprostol versus oral misoprostol (19.6% vs 10.9%, respectively, P=0.04). However, the authors noted no other significant differences in secondary maternal and neonatal outcomes, such as maternal hemorrhage and composite neonatal morbidity scores.

In addition to its retrospective nature, other limitations of the study include that the different time periods that each route of misoprostol was assessed may have affected study results.

But the authors noted that despite these limitations, the research remained strong in both its racial diversity and widely transferable outcomes.

"The doses of oral (50 micrograms) and vaginal [misoprostol] (25 micrograms) assessed in this analysis are among the most commonly used in the United States, and considered the safest doses per route," the authors said. "Future studies in different settings are required to assess the replicability and generalizability of these findings."