Background

Induction of labor (IOL) is the process of initiating labor by using medications, mechanical methods (devices), or other techniques, with the goal of achieving vaginal birth with minimal risks.¹ IOL has shown maternal/child benefit when the health of a pregnant woman or fetus is at risk (e.g., maternal hypertension or diabetes, fetal growth restriction, and in postterm pregnancies).^2,3 In addition to these medically-indicated deliveries, IOL is also done on an elective basis; reasons include scheduling at the request of pregnant women or to ensure availability of appropriate providers.⁴ A recent large randomized study of low-risk nulliparous pregnant women (the ARRIVE trial [A Randomized Trial of Induction Versus Expectant Management])⁵ demonstrated that induction of labor at 39 weeks, compared with expectant management, resulted in lower cesarean delivery rates and no difference in neonatal outcomes.^2,3 IOL rates are rising dramatically in the United States, reaching 25.7 percent in 2017.⁶ Labor induction occurs in approximately one-quarter of term pregnancies, with estimates of 77 to 85 percent due to medical indications.^7–9

Cervical ripening, often an initial component of labor induction, is the process of softening and effacing the cervix as well as stimulating early cervical dilation. Based on data from trials of labor induction, approximately 83 to 85 percent of women with an indication for induction require cervical ripening.^10,11 Common cervical ripening methods include pharmacologic options, such as prostaglandins (prostaglandin E1, misoprostol, and prostaglandin E2, dinoprostone), and mechanical options, such as inserting a balloon catheter or hygroscopic dilator into the endocervix. See Appendix A for descriptions of commonly used interventions, including contraindications for their use.

Traditionally cervical ripening has been performed as an inpatient procedure, and while there is variation, it can require substantial time and resources to accomplish successfully due to multiple factors. While prostaglandins (vaginal or oral) and mechanical methods (e.g., balloon catheters) are the most commonly used methods of cervical ripening in the inpatient setting, there is institution and provider-level variation in the dose, administration route and frequency of administration. Some women’s cervixes will rapidly respond to a cervical ripening intervention, while others require extended time with more than one intervention attempted if the first one fails. While interventions used for cervical ripening are generally not costly, the hospital inpatient resources used, including highly skilled labor and delivery staff, contribute to increased costs when cervical ripening care is provided in the inpatient setting.

For a variety of reasons, some women may prefer to be at home during the cervical ripening process, and because of the resources and variation involved, providers are also interested in exploring methods of cervical ripening in the outpatient setting that have minimal or no increased risk. Informed by these considerations, there is growing interest in, and evidence for, outpatient cervical ripening. It has been proposed that outpatient cervical ripening may facilitate more efficient and more satisfying IOL, also reducing inpatient length of stay compared to inpatient cervical ripening.

There are concerns regarding potential maternal/fetal risks of outpatient cervical ripening in comparison with the inpatient setting. These risks may be compounded by known and theoretical iatrogenic effects of medication and mechanical cervical stimulation. However, the risks of may be mitigated through the choice of cervical ripening method and clinical management. For example, prostaglandin use has been associated with tachysystole and fetal distress. Careful review of existing literature is needed to elucidate whether these outcomes occur more frequently when cervical ripening is accomplished in the outpatient versus inpatient setting and whether they increase fetal or maternal morbidity. In addition, maternal or fetal characteristics may differentially affect these risks. Finally, understanding the range of feasible outpatient cervical ripening options, and what form of fetal surveillance should be used (if any), is an important aspect of this review.

A woman’s preferences and satisfaction related to the setting of cervical ripening also need to be considered. Some may actively seek outpatient cervical ripening and others may strongly prefer inpatient cervical ripening. This likely variation in preferences and satisfaction has been identified as an important contextual question of this review.

Despite potential cost saving and sometimes strong personal preferences favoring outpatient cervical ripening, this approach to care is still debated. Controversy is driven by interpretation of risk, clinician’s discipline and experience (e.g., obstetrician vs. midwife),^12,13 and geographical practice variation. Clinician and institutional risk-aversion driven by potential legal litigation is also a consideration. The 2009 American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin on induction of labor summarized evidence on cervical ripening in the outpatient setting, based on only two studies available at that time (one on a prostaglandin, one on a single-balloon catheter),¹⁴ ultimately not reaching a recommendation. A 2017 Cochrane review found that evidence on outpatient versus inpatient cervical ripening was insufficient to address differences in maternal and fetal/neonatal health outcomes, such as cesarean delivery, between settings.¹⁵ This review included only randomized controlled trials, and included interventions not available in the United States, or that are used primarily to stimulate or maintain contractions rather than primarily for cervical ripening. Many cervical ripening studies have been conducted in non-U.S. settings, where patient acceptance and understanding of risk may be different, in addition to variation in provider philosophy and health system resources. There is a need to assess the benefits of outpatient versus inpatient cervical ripening, without increasing risk (rise in cesarean delivery rate, adverse neonatal outcomes), framed within considerations of cost, patient autotomy, and satisfaction. This is the crux of the decisional dilemma. When cervical ripening is indicated, what methods can be recommended as effective, but with no increased risks, in the outpatient setting and what surveillance best serves women induced with prostaglandin in the outpatient setting?

Purpose and Scope of the Systematic Review

This systematic review assessed the comparative effectiveness and potential harms of cervical ripening in the outpatient versus the inpatient setting, comparison of benefits and harms of different methods of cervical ripening in the outpatient setting, and evidence on benefits and harms of fetal surveillance during labor when a prostaglandin was used for cervical ripening in any setting. The intended audience includes the ACOG’s guideline developers, practitioners who deliver infants (e.g., obstetricians, family physicians, nurse-midwives), other personnel who administer and monitor cervical ripening, and health system policymakers. In addition to these clinical implications, we hope to inform the future research necessary to provide high-quality, evidence-based care to all pregnant women.