Authors
- Rydahl, Eva MHSc
- Eriksen, Lena MHSc
Abstract
Review question/objective: The objective of this review is to identify, assess and synthesize the best available evidence on the effects of induction prior to post-term (2 weeks past estimated date of delivery (EDD)) on the mother and fetus.
Background: Over the last two decades, a rather dramatic two- to four-fold increase in induction of labor rates has occurred within the developed world.1-3 The World Health Organization (WHO) has estimated that 25% of women in developed countries have their labor induced.1 There is no single reason for this marked rise in induction rates. Possible explanations raised in the literature are availability of cervical ripening agents, increasing demand from patients and a cultural shift towards more frequent use of interventions in childbirth including a liberal approach to elective induction.2, 3
Historically, induction of labor was performed to avoid conditions that could potentially harm mother or fetus (e.g. preeclampsia, intrauterine growth restriction, diabetes).4 According to the WHO, induction of labor should be performed only when there is a clear medical indication and the expected benefit outweighs potential harms. Studies suggest that between 25-50% of inductions are performed without a medical reason.5-7
This review examines the effects-harms and benefits-of routine induction of labor in 41+0 to 41+6 weeks of gestation compared to induction post term. A pregnancy is post term when it goes beyond the normal time of spontaneous delivery. Post term pregnancy is defined as two weeks past EDD.3 According to this review elective induction is performed by routine seven to 13 days past EDD (41+0-41+6 gestational weeks) which is within the normal range of pregnancy.
Some research has shown that routine elective induction may be beneficial to reduce some risks imposed by the ongoing pregnancy, such as the progress in development of preeclampsia, oligohydramnios, macrosomia, shoulder dystocia, postpartum hemorrhage; asphyxia, meconium aspiration syndrome; neonatal birth injury; lower umbilical artery pH; admission to Neonatal Intensive Care Unit and intrauterine fetal demise, which can develop into intrauterine death of the fetus at a later gestational age.2,8
On the other hand there is some evidence that induction itself is an independent risk factor of birth complications, which can increase fetal and maternal morbidity and possibly even mortality. The iatrogenic effect can be a longer labor, exposure to high-alert medicine with potential side effects of hyperstimulation, precipitate labor, uterine ruptures, meconium stained liquid, bleeding and fetal asphyxia.9. Research and experience has also clarified that an induced labor can cause a cascade of interventions such as intravenous line, continuous electronic fetal monitoring, amniotomy, confinement to bed, increased requirement for analgesia such as epidural, each with their own following potential complications and risk of iatrogenic harm.9
Influential obstetric medical societies and obstetric textbooks during the 1980s to about 2005 have been recommending induction or closer fetal surveillance, when pregnancies exceeded 14 days after EDD.10, 11 In 2008-2010 both English and North American obstetric societies and WHO changed the recommendations by changing the time for offering induction starting seven days past EDD, at 41+0 gestational weeks.1, 12, 13 The trend towards inductions prior to post term means that induction is performed by routine although the pregnancy is entirely within the normal range limits.14 Some authors have raised the concern that by inducing at 41+0 weeks, a large number of normal pregnancies may be put at risk from the iatrogenic consequences of induction. If induction is offered as early as one week past EDD (41+0), around 15-24% of women have not gone into spontaneous labor.15, 16 If induction is offered later, at weeks 42+0, 1-6% have not gone into spontaneous labor.15, 16 Induction prior to post term thus implies a huge rise in the number of a normal population needed to be treated. If there is even a slight increase in some adverse events caused by the intervention, this risk will be imposed on a large group within a healthy population and thereby cause many numeric cases of adverse events. When an intervention as routine induction is used on larger groups of people, it could also be costly through longer hospital stays and increased need of care.17, 18
A methodological problem with many studies covering the consequences of routine induction according to gestational age is the control group. Often the control group has very wide time limits for how long the pregnancy might last. Some studies accept expectant management until e.g. 44+0 weeks of gestation.2, 19 Accepting the evidence showing causality between post term pregnancies and intrauterine death, it is important that the control group is not exposed to any unnecessary risk of potential harm caused by excessively long pregnancies, which can overestimate the effect of induction prior to post term. Failure to go into spontaneous labor long beyond term can even be related to pathological conditions e.g. some malformations or severe obesity.3, 20 This review will eliminate this potential source of bias by considering for inclusion only, studies which compare routine induction prior to post term with routine induction post term defined as 42+0 gestational weeks.
Definitions: For the purpose of this review, the following definitions will be used:
Low risk pregnancy: A low-risk pregnancy is one where the mother and baby are not affected by conditions or circumstances that can complicate the birth. This includes a singleton pregnancy, vertex presentation, with no known risk factors or complications, and with a normally grown and formed baby.21
Elective induction: Is defined as any intervention with the aim of inducing labor, performed before the spontaneous onset of labor and with no recognized fetal or maternal compromise.22
Post term: A pregnancy is post term when it reaches two weeks past the EDD, or 42+0 weeks or 294 days of gestation.3
Prior to post term: In this study, we define "prior to post term" as the pregnancy time period between 41+0 and 41+6 weeks or between 287 to 293 days of gestation.
The motivation for this review needs to be understood in the context of the increasing trend towards inducing labor prior to the post term date traditionally understood to be best practice, and the need to establish whether this has significant negative impacts on mothers and babies. A second motivator for this review is that a search of PubMed, Cochrane, Web of Science and JBI Database of Systematic Reviews and Implementation Reports did not identify any reviews on this topic, and there is no protocol currently registered for such a review.
Article Content
Inclusion criteria
Types of participants
The participants to be included in this review are pregnant women at low risk of complications at the time of enrolment. To be included, both the fetus and the mother should be healthy with no known risk besides the potential risk of the ongoing pregnancy. There should be intended vaginal birth with no contraindications. The estimated date of delivery should be made by ultrasound to obtain reasonably comparable measures of pregnancy length estimation.
Types of intervention and comparator
The intervention to be considered in this review is routine induction prior to post term pregnancy, which in this review is defined as induction at 41 weeks and 0-6 days (41+ 0/6 gestational weeks). The comparator group is no induction at 41+ 0/6 gestational weeks and, thus, awaiting spontaneous onset of labor /or induction of labor post term, i.e. at 42+ 0/6 gestational weeks.
The intervention often depends on an individual assessment of the cervical status of the woman. Studies will be included, if they examine generally accepted induction methods: With an unfavorable cervix the induction agent can either be prostaglandins PGE1/ PGE2 or Foley catheter. On a favorable cervix artificial rupture of membranes (ARM) followed by oxytocin or solely oxytocin or solely ARM can be used as an induction agent.23
Types of outcomes
All outcomes of interest are related to either prolonged pregnancy or induction of labor. The outcomes of interest in this review relate to child/fetus and mother wellbeing. The primary outcomes of interest are cesarean section and low Apgar score (<=7/5 min). Secondary outcomes are:
Maternal: postpartum hemorrhage; need for epidural; instrumental delivery; dystocia; episiotomy; three to four degree lacerations; uterine rupture; length of hospital stay; infection; success rate for breastfeeding.
Fetal: hyperstimulation; pathological Cardiotocography (CTG); hospitalization at neonatal intensive care unit (NICU); meconium aspiration; shoulder dystocia; infection; cerebral palsy; brachial plexus injury; hypoxic-ischemic encephalopathy and mortality.
The outcomes of interest are measured differently in different studies. We aim to adopt an inclusive approach and include and describe the range of measures. Details on measurement of outcome will be specified and any limitations considered in the analyses.
Types of studies
This review will consider for inclusion both experimental and non-experimental study designs including randomized controlled trials, non-randomized controlled trials, quasi-experimental, prospective and retrospective cohort studies. Despite the risk of selection bias in cohort studies, these will be included for consideration as large scale studies are needed to investigate rare but serious outcomes as mortality or low Apgar scores.
To be considered for inclusion a study must have examined and compared the effects of interest either on mother or child or both of post term induction versus induction prior to post term. Studies will be included if they focus on benefits or harms or both as long as they use the outcomes of interest.
Search strategy
A three-step search strategy will be utilized in this review. The strategy will aim to find both studies published in peer reviewed journals as well as grey literature. The initial search terms, identified below, were selected based on discussion with a research librarian to secure identification of the maximum number of relevant articles.
An initial limited search of PubMed and CINAHL will be undertaken followed by analysis of the text words contained in the title and abstract, and of the index terms used to describe article. A second search using all identified keywords and index terms will then be undertaken across all included databases. Thirdly, the reference list of all identified reports and articles will be searched for additional studies.
Studies published in English, Danish, Swedish and Norwegian will be considered for inclusion in this review. Authors of primary studies will be contacted for missing information or to clarify unclear data.
According to the rapid change in management of induction and in change of methods for estimating date of delivery, only studies published within the last 2 decades, since 1994, will be considered and a date limit of 1994-2014 will be applied. The databases to be searched will include:
PubMed, CINAHL, Embase, Scopus, Swemed+, POPLINE; Cochrane, TRIP; Current Controlled Trials; Web of Science.
Additional searching for published literature will include:
Hand searching reference lists and bibliographies of included articles.
The search for grey literature will include:
MedNar; Google Scholar, ProQuest dissertations and theses, Guidelines from RCOG and ACOG
The initial keywords to be used are:
Pregnancy
AND
Low risk OR Normal OR Term
AND
Post term OR Prolonged OR Prolonged pregnancy OR Post-date OR Past due date OR Beyond term
AND
Induced labor laborOR Induction OR Cervical Ripening OR Labor, induced OR Elective induction OR Routine induction OR Expectant management
AND
Adverse OR Adverse effects OR Adverse events OR Caesarian section OR Mortality OR Morbidity
Assessment of methodological quality
Papers selected for retrieval will be assessed by two independent reviewers for methodological validity prior to inclusion in the review using standardised critical appraisal instruments from the Joanna Briggs Institute Meta-Analysis of Statistics Assessment and Review Instrument (JBI-MAStARI) (Appendix l). Any disagreements that arise between the reviewers will be resolved through discussion, or with a third reviewer.
Data collection
Data will be extracted from papers included in the review using the standardised data extraction tool from JBI-MAStARI (Appendix ll). The data extracted will include details about the interventions, populations, study methods and outcomes of significance to the review question and specific objectives.
Data synthesis
Quantitative papers will, where possible be pooled in statistical meta-analysis using JBI-MAStARI. All results will be subject to double data entry. Effect sizes expressed as odds ratio (for categorical data) and weighted mean difference (for continuous data) and their 95% confidence intervals will be calculated for analysis. Heterogeneity will be assessed statistically using the standard Chi-square and also explored using subgroup analysis based on the different quantitative study designs included in this review. Where statistical pooling is not possible the findings will be presented in narrative form with tables and figures used where appropriate to facilitate interpreting the results of the included studies.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
Mette Juhl,Midwife, MPH, PhD, Postdoc, The Research Unit Women's and Children's Health, The Juliane Marie Centre, Copenhagen University Hospital, Rigshospitalet, Copenhagen.
Bodil K. Moller, Head of Midwifery Program at University College Metropol, RM, BSW, MVO; Copenhagen.
Search librarian Anna Mobjerg; University College Metropol; Copenhagen.
References
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Appendix I: Appraisal instruments
MAStARI appraisal instrument[Context Link]
Appendix II: Data extraction instruments
MAStARI data extraction instrument[Context Link]
Keywords: Adverse events; iatrogenic; induction of labor; normal pregnancy; post term