Excessive uterine activity accompanying induced labor

doi:10.1016/S0029-7844(01)01332-1

Obstetrics & Gynecology

Volume 97, Issue 6, June 2001, Pages 926-931

https://doi.org/10.1016/S0029-7844(01)01332-1 Get rights and content

Abstract

Objective: To estimate the incidence and timing of excessive uterine activity accompanying induction of labor with misoprostol using different routes (oral or vaginal) and forms (intact tablet or crushed) and to compare these with dinoprostone gel, oxytocin, and spontaneous labor.

Methods: This retrospective cohort study included 519 women at term who had labor induced and 86 women at term in spontaneous labor. Induction agents included misoprostol, dinoprostone, or oxytocin. Fetal heart rate and uterine activity tracings were analyzed independently by three maternal-fetal medicine physicians. The diagnosis of tachysystole or hyperstimulation required the agreement of two or more reviewers.

Results: The incidence of tachysystole was highest with misoprostol administered by vaginal tablet (misoprostol vaginal tablet 50 μg every 4 hours, 48.6%; vaginal tablet crushed 50 μg and suspended in hydroxyethyl gel every 4 hours, 30.7%, P = .009; oral tablet 50 μg every 4 hours, 22.2%, P = .001; oral tablet crushed 50 μg every 4 hours, 15.5%, P < .001; dinoprostone gel, 33.0%, P = .022; intravenous oxytocin, 30.2%, P = .027; and spontaneous onset of labor, 23.3%, P < .001). Hyperstimulation occurred more often with dinoprostone gel (16.5%) than with other forms of induction or spontaneous labor. Hyperstimulation occurred significantly more often with vaginal misoprostol crushed tablet (7.9%) and vaginal misoprostol intact tablet (7.6%) than with crushed oral misoprostol (1.0%) (P = .016 and .018, respectively). There was a shorter time to tachysystole with increasing doses of vaginal misoprostol tablet (P = .01).

Conclusion: The incidence of tachysystole and hyperstimulation, and time to tachysystole, varied depending on the route and form of misoprostol given.

Section snippets

Methods

This retrospective cohort study was performed at the Grace General Hospital, St. John’s, Newfoundland, Canada from March 30, 1994 to December 19, 1997. This provincial tertiary care center serves an almost entirely white population and is the site of 2400 of the province’s 5500 annual births. The study included women enrolled in each of three randomized controlled trials evaluating misoprostol for labor induction,13, 14, 15 as well as a cohort of women who presented in spontaneous labor during

Results

Five hundred nineteen women who had labor induced and 86 women admitted in spontaneous labor were included in the study. The demographic characteristics of these women have been described previously (except for the spontaneous labor cohort).13, 14, 15 Table 1 summarizes the incidence of excessive uterine activity, including tachysystole and hyperstimulation, in each group. Tachysystole occurred more frequently with the misoprostol vaginal tablet than other forms or routes of induction or

Discussion

The incidence of tachysystole with misoprostol, although high, is in keeping with results of earlier studies.1, 2 By using a strict definition and several physicians reviewing the tracings we were able to better estimate its true incidence. We found a higher rate of tachysystole when misoprostol was given as an intact tablet vaginally compared with gel form or oral administration. Hyperstimulation occurred more frequently with vaginal administration compared with the crushed form given orally.

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Normal labor and delivery are dependent on the presence of regular and effective contractions of the uterine myometrium. The mechanisms responsible for the initiation and maintenance of adequate and synchronized uterine activity that are necessary for labor and delivery result from a complex interplay of hormonal, mechanical, and electrical factors that have not yet been fully elucidated.
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Currently, different methods exist for evaluating uterine activity during labor, including manual palpation, external tocodynamometry, intrauterine pressure monitoring, and electrical uterine myometrial activity tracing. Legacy uterine monitoring techniques have advantages and limitations. External tocodynamometry is the most widespread tool in clinical use owing to its noninvasive nature and its ability to time contractions against the fetal heart rate monitor. However, it does not provide information regarding the strength of uterine contractions and is limited by signal loss with maternal movements. Conversely, the intrauterine pressure catheter quantifies the strength of uterine contractions; however, its use is limited by its invasiveness, risk for complications, and limited additive value in all but few clinical scenarios. New monitoring methods are being used, such as electrical uterine monitoring, which is noninvasive and does not require ruptured membranes. Electrical uterine monitoring has yet to be incorporated into common clinical practice because of lack of access to this technology, its high cost, and the need for appropriate training of clinical staff. Further work needs to be done to increase the accessibility and implementation of this technique by experts, and further research is needed to implement new practical and useful methods. This review describes current clinical tools for uterine activity assessment during labor and discusses their advantages and shortcomings.
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When used for cervical ripening or induction of labor, 25 micrograms (mcg) placed in the posterior vaginal fornix should be considered for the initial dose (ACOG, 2009b; FIGO, 2017). Tachysystole and indeterminate or abnormal FHR changes have been associated with both the 25-mcg and the 50-mcg doses (Crane, Young, Butt, Bennett, & Hutchens, 2001; Kreft et al., 2014; McMaster et al., 2015; Penfield & Wing, 2017). Higher dosages have been associated with an increased rate of tachysystole (ACOG, 2009b; Kreft et al., 2014; McMaster, Sanchez-Ramos, & Kaunitz, 2015; Penfield & Wing, 2017; Stephenson & Wing, 2015).
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An important risk factor for tachysystole is induction of labor. Specifically, tachysystole is associated with exposure to prostaglandins for cervical ripening, as well as oxytocin.65,69,70 The concern with tachysystole lies in its association with the development of fetal acidemia.
Contractions are produced through a complex interplay of hormonal, mechanical, and electrical factors. In labor, contractions are measured using the Montevideo unit. Clinical considerations in labor wherein contraction assessment becomes paramount include the care of women whose labor is complicated by abnormal progress or tachysystole. In an era of obstetrics in which the high cesarean rate is a major issue of concern, there remain many questions as to how to best incorporate contraction monitoring into practice in order to optimize care. Technological advancement has led to the development on new modalities that can be used to study contraction physiology, and there may be an opportunity in the future to apply these methods for use in the clinical setting. This article also makes a case for the need to reevaluate the current measures of uterine contractile activity and the definition of contraction adequacy using updated definitions of normal labor progress.

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Excessive uterine activity accompanying induced labor

Abstract

Section snippets

Methods

Results

Discussion

J Soc Obstet Gynaecol (Canada)

Obstet Gynecol

Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

Obstet Gynecol

Obstet Gynecol