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Development of a core outcome set for effectiveness studies of breech birth at term (Breech-COS): A systematic review on variations in outcome reporting

      Highlights

      • Systematic review of outcomes reported in studies concerning breech births at term.
      • Supported decision-making and evidence synthesis hampered by inconsistent outcome measures.
      • Wide range and heterogeneity in reported outcomes identified.
      • Lack of consensus in definition and measurement observed.
      • Patient-centred care targeted by involvement of PPI group in COS development.

      Abstract

      Women pregnant with a breech-presenting fetus at term are at an increased risk of adverse outcomes. Although the most common intervention is planned delivery by caesarean section, this is not always possible or desirable. Comparing alternative interventions is difficult due to heterogeneity in reported outcomes and their measurements. Additionally, the evidence, particularly for women in labour with a breech-presenting fetus, is very low quality, with several outcomes viewed as critical and important to decision-making not reported at all. There is a need to develop a core outcome set of minimum outcomes in all studies evaluating the effectiveness of interventions to improve outcomes associated with term breech birth (Breech-COS).
      Our objectives were to (1) identify outcomes currently reported in effectiveness studies of breech birth at term using a systematic review of the literature; (2) assess the methodological quality of outcome reporting in the included studies; and (3) engage with members of an established Patient and Public Involvement (PPI) group about the results, to help frame our understanding from the perspective of service users.
      We searched three databases (MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials) for all effectiveness studies associated with vaginal breech birth published in English between 2000 and 2020. Two reviewers independently screened and extracted the data. Outcomes were categorised into neonatal, maternal, features of labour, and long-term maternal and hierarchy of outcome classification (primary, secondary, part of composite, or undesignated). Frequency of reporting was calculated for each. An adapted methodological assessment was done for each study investigating whether primary and secondary objectives were clearly stated and defined. The results of the systematic review were then discussed with a PPI group to consider importance and relevance to service users.
      A total of 211 outcomes were extracted from 108 included studies, comprising of short (43) and long-term (39) neonatal, short (54) and long-term (39) maternal and features of labour (36) outcomes. The most frequently reported outcome in each category was: APGAR score at 5 min, developmental vulnerability/neurological morbidity, maternal mortality, urinary incontinence, and actual mode of birth respectively. Long-term outcomes were infrequently reported in the included studies, with outcomes for future pregnancies not reported at all, although these were each deemed important by service users. There was a lack of consensus in definition and measurement of outcomes, with only 36% of the included studies having clearly stated primary and secondary objectives.
      The observed heterogeneity in reported outcomes, lack of consensus in definition and measurement, as well as desire expressed by service users to have robust risk statistics for outcomes important to them highlights the need to develop a core outcome set for evaluating effectiveness studies of breech birth at term. A Breech-COS will enable useful synthesis of evidence and contribute to supported decision-making for women pregnant with a breech-presenting fetus at term.

      Keywords

      Nomenclature

      Abbreviations and Definitions

      APH
      Antepartum haemorrhage
      ARDS
      Acute respiratory distress syndrome
      Breech
      Refers to a foetus, lying in a longitudinal position, with buttocks, feet, or knees closest to the cervical os (bottom of the uterus)
      Breech-COS
      Core outcome set for evaluation of studies of breech birth at term
      CS
      Caesarean section
      CENTRAL
      Cochrane Central Register of Controlled Trials
      COMET
      Core Outcome Measurement in Effectiveness Trials
      COS
      Core outcome set
      CPAP
      Continued air pressure pathway
      CROWN
      Core Outcomes in Women’s and Newborn Health
      D + C
      Dilation and curettage
      DAMP
      Deficits in attention, motor control, and perception
      DIC
      Disseminated intravascular coagulation
      DVT/PE
      Deep vein thrombosis/pulmonary embolism
      ECV
      External cephalic version
      IQ
      Intelligence quotient
      NEC
      Necrotising enterocolitis
      NICU
      Neonatal intensive care unit
      PPH
      Post-partum haemorrhage
      PPI
      Public and patient involvement
      PSC
      Project steering committee
      Term
      Refers to a term pregnancy, defined as a gestation greater than 36 weeks 5 days and less than 42 weeks 0 days
      VBB
      Vaginal breech birth

      Introduction

      Women pregnant with breech presenting foetus at term are at an increased risk of adverse pregnancy outcomes [
      • Impey L.
      • Murphy D.
      • Griffiths M.
      • Penna on behalf of the R. C. of O. G. Management of Breech Presentation L.
      ]. Planned delivery by caesarean section (CS) is the most common intervention used to improve neonatal outcomes [
      • Hofmeyr G.J.
      • Hannah M.
      • Lawrie T.A.
      Planned caesarean section for term breech delivery.
      ]. However, prior planning is not always possible, and some women may prefer to give birth vaginally. Although alternative interventions have been proposed by many providers, heterogeneity in the reported outcomes [
      • Hofmeyr G.J.
      • Kulier R.
      • West H.M.
      Expedited versus conservative approaches for vaginal delivery in breech presentation.
      ] acts as a barrier to meaningful comparisons. Careful selection of primary and secondary outcomes is a crucial component of clinical trial design [
      • Williamson P.R.
      • et al.
      Developing core outcome sets for clinical trials: Issues to consider.
      ]. Heterogeneity in outcomes measured within the same clinical area, including inconsistency about the broad domains considered, the outcomes themselves, the way these outcomes are labelled and defined, and the methods and timing of measurement, can complicate or prevent useful synthesis and meta-analysis [

      Higgins, J. et al., Cochrane Handbook for Systematic Reviews of Interventions. Cochrane Collaboration (Cochrane. Available from www.training.cochrane.org/handbook., 2019).

      ]. Standardised reporting of outcomes and their measurement enables the direct comparison of effects of different interventions across multiple studies, thereby improving the quality of research and minimising bias [
      • Williamson P.R.
      • et al.
      Developing core outcome sets for clinical trials: Issues to consider.
      ].
      This literature review was the first step in developing a core outcome set (COS), the first for studies evaluating effectiveness of interventions to improve outcomes in breech births at term, to be titled Breech-COS. A COS is a minimum set of key standardised outcomes, agreed upon by all relevant stakeholders, that should be measured and reported in all trials for the specific clinical field [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ]. The Cochrane Collaboration [

      Higgins, J. et al., Cochrane Handbook for Systematic Reviews of Interventions. Cochrane Collaboration (Cochrane. Available from www.training.cochrane.org/handbook., 2019).

      ], the Core Outcome Measurement in Effectiveness Trials (COMET) Initiative [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ], and the Core Outcomes in Women’s and Newborn Health (CROWN) Initiative [
      • Duffy J.
      • et al.
      Core outcome sets in women’s and newborn health: a systematic review.
      ] all recommend developing a COS to improve synthesis of evidence. Conducting a systematic review of outcomes is an efficient way to identify an inclusive list of outcomes being reported by researchers in the field [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ]. Additionally, outcomes reported in trials may not be meaningful endpoints for service users [
      • Williamson P.R.
      • et al.
      Developing core outcome sets for clinical trials: Issues to consider.
      ]. Therefore, the COMET Initiative recognises that COS need to include outcomes that are important to patients and carers, in order for care to be person-centred, and recommend incorporating Public and Patient Involvement (PPI) groups in COS development [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ].
      We undertook a systematic literature review to identify outcomes, definitions and measurements previously reported in effectiveness studies of breech births at term and involved the study’s PPI group to discuss their importance to service users, as a preliminary exercise to formal participation in the Breech-COS Delphi survey. The results of this review will be included in the international Delphi survey for Breech-COS and will be open to all key stakeholders for consensus development. Breech-COS is part of a larger project that seeks to evaluate an alternative model of care, “The OptiBreech care pathway: evaluating the feasibility and acceptability of team care for women seeking to plan a vaginal breech birth” (NIHR 300582).
      Breech-COS has been registered with the COMET Initiative (www.comet-initiative.org; #1749) and has been submitted to the CROWN Initiative.

      Objectives

      The overall aim of Breech-COS is to identify a core outcome set for effectiveness studies of breech birth at term by an international multi-stakeholder consensus method. Breech-COS is intended as the international standard for randomised and non-randomised effectiveness studies of breech births in term pregnancies. This review is the first stage of the Breech-COS development. The specific objectives are in accordance to the four steps of developing a COS, as outlined by the COMET Initiative, namely: (1) conceptual considerations, (2) finding existing outcome measurement instruments using a systematic review, (3) quality assessment of existing instruments, and (4) recommendations for selection of outcomes included in COS using a consensus process [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ].
      The primary objective of this systematic review was:
      • 1.
        To identify outcomes currently reported in comparative studies concerning breech birth at term by way of a systematic review of the literature.
      The secondary objectives were:
      • 1.
        To identify the methodological quality of outcome reporting in existing studies; and
      • 2.
        To engage with members of an established Patient and Public Involvement (PPI) group about the results, to help frame our understanding from the perspective of service users

      Methods

      Search strategy and selection criteria

      The methods and criteria for study selection were developed in accordance with the scope of Breech-COS, and in consultation with the research team as well as the Project Steering Committee (PSC), which includes breech-experienced obstetricians, midwives and service users. The databases searched were EMBASE, MEDLINE, and Cochrane Central Register of Controlled Trials (CENTRAL). Full terms of a comprehensive, electronic search strategy are included in the supplementary material (Supplementary Material 1).
      The eligibility criteria were designed to identify the choice and consistency of outcomes reported in comparative studies concerning vaginal breech birth (VBB). Studies not describing breech birth outcomes, conference proceedings or abstracts without complete trial description were not included. Eligible participants were all childbearing people ≥ 37 weeks pregnant with a foetus in breech presentation. Eligible interventions included planned modes of delivery (planned VBB vs. planned CS), methods of management for VBB (upright vs. supine, expediated vs. conservative, assisted delivery), and models of care delivery (different experience levels, professions, breech teams).
      The eligibility criteria were:
      • Settings: both high- and low-income
      • Language: English language,
      • Time: 2000 to 2020
      • Study design: systematic reviews, randomised trials, comparative observational studies
      The time period was chosen as the ‘Term Breech Trial’, a single large randomised trial, was published in 2000 [
      • Hannah M.E.
      • et al.
      Planned caesarean section versus planned vaginal birth for breech presentation at term: a randomised multicentre trial.
      ]. Two other small trials completed before 2000 are included in the Cochrane Review last updated in 2015 [
      • Hofmeyr G.J.
      • Hannah M.
      • Lawrie T.A.
      Planned caesarean section for term breech delivery.
      ]. The scoping search revealed no other trials in this time period.
      Two of the four review authors (SW, AH, AR, TD) independently screened the title and abstracts returned by the search strategy, followed by full-text screening to determine eligibility. A third reviewer was consulted to moderate and resolve disagreements, in cases of discrepancy. Covidence systematic review software [

      Veritas Health Innovation. Covidence systematic review software. (2020).

      ] was used to record the screening process. Independent data extraction was then performed for each article using a Microsoft Excel spreadsheet-based extraction form for the following: author and title details, year and journal of publication, study type, setting, key eligibility criteria, study population size, description of intervention, proposed outcomes, primary and secondary effectiveness and safety outcome(s) reported, outcome definition(s), outcome measurement tool(s) and timing(s). Original study authors were contacted in cases of unclear or unavailable data.
      Outcomes were categorised into measures associated with each of the five following: short- and long-term neonatal, short- and long-term maternal, and features of labour. Frequency of reporting for each outcome was calculated, and each was designated as a primary, secondary, part of a composite, or reported but not designated; as per the outcome framework by the COMET Initiative [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ]. For the features of labour outcome group, an additional designation of group was also assigned, if the measure acted as a subject group in the study. The subsequent Delphi survey for prioritisation of outcomes by stakeholders will also be informed by these categories.

      Assessment of methodological quality

      The methodological quality of reported outcomes in included studies were assessed using the four questions as below [
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ,
      • Smith V.
      • et al.
      Protocol for the development of a salutogenic intrapartum core outcome set (SIPCOS).
      ] rather than performing a traditional assessment of individual studies.
      • 1.
        Is the primary outcome clearly stated?
      • 2.
        Is the primary outcome clearly defined so that another researcher would be able to reproduce its measurement (e.g., measurement tools, measurement timing)?
      • 3.
        Are secondary outcomes clearly stated?
      • 4.
        Are secondary outcomes clearly defined?
      A scoring system was devised where each article was scored from 1 to 4 depending on how many of the questions were answered. The frequency of each quality score was then calculated.

      PPI group involvement

      The summary of findings from the systematic review were brought to the OptiBreech study’s pre-established PPI group in an online meeting led by members of the review team [SW and TD]. The meeting was advertised on the project website (OptiBreech.uk) as well to invite parents with experience of breech birth. The purpose of this stage was to gain insight into (1) how service users with experience of breech birth value the outcomes identified in published literature, including their importance and relevance; and (2) to identify any outcome measures that are deemed important by the PPI group but were not identified by the systematic review. This was to enable the PPI group to have significant influence on the subsequent Delphi process from the start of the survey. The meeting was recorded, and key themes and points of discussion obtained from the meeting transcript. Understanding was checked with participants repeatedly during the meeting. No identifiable information or direct quotes were collected or preserved.

      Results

      Our search identified 817 records in total, of which 13 were duplicates and 629 were deemed irrelevant based on title and abstract screening. Full text was assessed for the remaining 147 articles and 39 were removed due to various reasons such as full-text not available in English, wrong patient population etc. Finally, data was extracted for 108 studies, as presented in the PRISMA flow chart in Fig. 1. The 108 articles included comprised of reviews with or without meta-analysis, randomised controlled trials, and non-randomised observational studies from various settings: low-, middle-, and high-income countries; at home birth vs. tertiary care centre; and comparing various interventions: mode of delivery (e.g., VBB, external cephalic version, CS), models of service provision (e.g., staff training levels, hospital birth volume), management of delivery (e.g., upright position vs. supine, manoeuvres used, induction), or no intervention. A full record of the characteristics of each article included in this review is provided in the supplementary material (Supplementary material 2).
      Figure thumbnail gr1
      Fig. 1PRISMA flow chart of review screening and inclusion process.

      Outcomes

      We extracted 211 total outcomes, divided into short-term neonatal (43), long-term neonatal (39), short-term maternal (54), long-term maternal (39), and features of labour (36). Frequency of reporting and outcome hierarchy designation for each of these is provided in detail in Table 1. In the 108 included reviews, the most frequently reported outcome was mode of birth: vaginal birth in 93.5%, elective CS in 76.8%, and emergency CS in 72.2% articles. Some studies compared only vaginal birth vs emergency or elective CS, but not both; others were concerned with the results of vaginal births only. However, most studies reported mode of birth as a subject group, i.e., authors compared various outcomes between vaginal breech birth vs. elective CS vs. emergency CS.
      Table 1Full list of outcomes with frequency or reporting and categorisation of outcome.
      OutcomesTotalPSNC
      Short-term neonatal
      APGAR score at 5 min841594614
      Perinatal mortality (includes intrapartum and/or neonatal only)73243379
      Admission to neonatal intensive care unit (NICU)621372913
      Neonatal birth trauma/morbidity (incl. any of following)561142120
      Brachial plexus injury/peripheral nerve injury39741117
      Low umbilical artery PH3956253
      Bone fracture (clavicle/basal skull/humerus/femur)36621216
      Neonatal seizures/convulsions3291715
      Intubation/ventilation31511213
      Hematoma (cephalo- or subdural- or not specified)2962813
      Composite neonatal outcome27134100
      intracerebral bleeding/laceration or haemorrhage2662513
      APGAR score at 1 min2211200
      Tube feeding216159
      Spinal cord injury2041213
      Significant genital injury1730212
      Neonatal asphyxia1632101
      Respiratory distress syndrome/meconium aspiration154173
      Cord blood base deficit145243
      Hypotonia135125
      Stupor/decreased response to pain/coma103034
      Foetal acidaemia/acidosis94041
      APGAR score at 10 min81160
      Cord blood base excess81142
      Admission to intermediate unit82141
      Difficulty with delivery of after coming head70070
      Intrauterine Stillbirth61041
      Hip dislocation50050
      Low APGAR score50140
      Assisted ventilation after delivery (greater than30mins)53011
      Neurologically normal at 6 weeks52030
      Hyperbilirubinemia41030
      Other birth injury30021
      Perinatal infection31110
      Paresis or paralysis32010
      Lacerations to baby buttocks20020
      Transfer to higher service level hospital20011
      Venous cord blood PH10010
      Umbilical cord lactate10100
      External heart massage required at birth10010
      Neonatal hypoglycaemia10010
      Surgical procedures10001
      Jaundice10010
      Long-term neonatal
      Developmentally vulnerable/special needs/neurological morbidity2033140
      Diagnosis of cerebral palsy115060
      Developmental delay or learning disability (incl. non-verbal cognition, social-emotional development, language deficiencies)112180
      Neonatal encephalopathy83230
      Infant mortality (up to 1 year)71240
      Congenital malformation/defect60150
      Speech/language problems61050
      motor development50050
      Autism51040
      Any medical problem at 2 years50230
      Child follow up in outpatient care/ Hospitalisation51040
      Epilepsy41030
      Visual defect41030
      Auditory defect41030
      Pedagogical support in school41030
      Short term problems with breathing/bradycardia41030
      Hypoxia40040
      Developmental dysplasia of the hip30030
      Need for resuscitation30021
      Continuous Positive Airway Pressure (CPAP)32001
      Facial palsy31101
      Childhood mortality21010
      Deficits in Attention, Motor Control and Perception (DAMP) or DAMP related symptoms20020
      No unassisted walking20020
      Pedagogical support in kindergarten21010
      Speech/language support21010
      Special childcare support21010
      Poor infant health (general)11000
      Spasticity10010
      Hyperactivity11000
      Level of educational attainment10010
      Necrotizing enterocolitis (NEC)11000
      Long term medication10010
      Ordinary childcare support10010
      Increased childcare support10010
      Low intelligence quotient (IQ)10010
      Asthma10010
      Postponed school start10010
      Low scores on school tests10010
      Short-term maternal
      Maternal mortality2353150
      PPH requiring blood transfusion163571
      Genital tract trauma1614101
      Other serious maternal morbidity/other complications151482
      Wound infection requiring prolonged hospital stay/readmission/antibiotics131561
      Postpartum haemorrhage (PPH) transfusion not specified110470
      Deep vein thrombosis/Pulmonary embolism (DVT/PE) requiring anticoagulant therapy110371
      Prolonged hospital stay111361
      Gestational Diabetes Mellitus101090
      Hypertensive disorder/Preeclampsia91080
      Hysterectomy80242
      PPH not requiring transfusion70250
      Vulvar or perineal haematoma requiring evacuation70331
      Maternal fever of 38.5 or above on two occasions at least 24 h apart not including first 24 h71321
      Anaemia62130
      Placental separation/abruption60060
      Bladder, ureter or bowel injury requiring repair60141
      Wound dehiscence/breakdown51112
      Genital tract fistula50131
      Cystitis/urinary retention/tract infection50041
      Endometriosis50140
      Dilation and curettage (D + C) for bleeding/retained placental tissue40121
      Uterine Rupture40130
      Puerperal infections40040
      Pre-existing Diabetes40040
      Antepartum haemorrhage (APH)30030
      Cervical laceration involving lower uterine segment30111
      Acute respiratory distress syndrome (ARDS)/Mechanical ventilation30102
      Bowel/intestinal obstruction30111
      Admission to ICU33000
      Ileus30021
      Composite maternal outcome20020
      retained placental tissue/manual removal of placenta20101
      Vertical uterine incision or serious extension to transverse uterine incision20101
      Pneumonia20101
      Readmission20011
      Wall abscess/postoperative hematomas20020
      Moderate trauma relating to obstetrical or surgical manoeuvres20020
      Sepsis22000
      Endomyometritis20110
      Postpartum antibiotic treatment20200
      Intracranial/Cerebrovascular haemorrhage10001
      Cardiac Arrest10001
      Isolated hyperthermia10010
      Pyelonephritis10010
      Disseminated intravascular coagulation (DIC)10010
      Intestinal injuries10010
      Additional Surgery10100
      Organ Failure11000
      Hypotension10001
      Prolonged vaginal bleeding10010
      Laparotomy10010
      Relaparotomy10010
      Early depression10100
      Long-term maternal
      Urinary incontinence73130
      Faecal incontinence73130
      Breastfeeding complications63120
      Postnatal depression52210
      CS in subsequent delivery52120
      Long term perineal pain43100
      Long term abdominal pain43100
      Dyspareunia43100
      Any pain42110
      Flatus incontinence42110
      Relationship with partner42110
      Subsequent pregnancy41120
      Maternal satisfaction42110
      Back pain/back ache32100
      Relationship with baby31110
      Uterine rupture in subsequent delivery31110
      Postnatal anxiety20110
      Infertility20110
      Miscarriage or termination in subsequent pregnancy20110
      Menorrhagia21100
      Breech presentation in subsequent pregnancy21010
      Fatigue/tiredness21010
      Constipation21010
      Pain during sex21010
      Had sex in last 36 months21010
      Happiness with sexual relations22000
      Ease of caring for child22000
      Experience of motherhood22000
      Uterovaginal prolapse10100
      Postnatal self esteem10100
      Genital dystopia (characterised by rectovaginal prolapse or enterocele)11000
      Dysmenorrhea10100
      Painful menstrual periods11000
      Irregular menstrual periods11000
      Haemorrhoids11000
      Vaginal discharge11000
      Relationship with partner compared to when baby was born11000
      Visited doctor since birth11000
      Childbirth experience11000
      OutcomesTotalPSNCG
      Features of labour
      Vaginal Breech Delivery10112020069
      Elective caesarean837116059
      Emergency Caesarean789127041
      Actual mode of birth467128010
      Planned mode of birth332113017
      Induction of labour33102804
      Trial of labour/ Failure to progress23202100
      Manoeuvres used21101802
      Instrumental vaginal delivery20011900
      Regional anaesthesia18011700
      Duration of delivery/second stage17001700
      Premature rupture of membranes17001700
      Medical staff management/decision/ adherence to TBT16002014
      Type of Breech/Maternal characteristics15001203
      Augmentation of labour15001500
      ECV1510806
      Abnormal tracing in labour/Foetal monitoring14001202
      Duration of first stage13001300
      Umbilical cord prolapse13001300
      Vaginal Cephalic Delivery1110307
      Maternity unit activity/ Type of hospital800404
      Chorioamnionitis700700
      VBB attempt621102
      General anaesthesia601500
      Cord presentation500500
      Nuchal cord500500
      Maternal choice in mode of delivery (incl. information source/support/safety)501301
      Precipitous labour300300
      Oligohydramnios300300
      Non vertex presentation at birth200200
      Uterine contraction100100
      Antibiotic use in labour100100
      Meconium staining100100
      Meconium aspiration110000
      Colour of amniotic fluid100100
      P-primary; S-secondary; N-undesignated; C-part of composite; G-as a subject group.
      On average, neonatal outcomes were reported in a more studies as compared to maternal outcomes (11.1% vs. 3.7%), with very few reporting long term or salutogenic outcomes for either. Amongst short-term neonatal outcomes, APGAR score at 5 min was the most commonly reported outcome, reported in 77.7% studies. This was followed by perinatal death (67.5%) and admission to NICU (57.4%). The three most reported long-term neonatal outcomes were developmental vulnerability/special needs/neurological morbidity (18.5%), cerebral palsy (10.1%) and developmental delay/learning disability (10.1%).
      The most frequently reported short-term maternal outcome was maternal mortality, measured in 21.2% studies. Postpartum haemorrhage (14.8%) and requiring blood transfusion (14.8%) were the next two most frequent. Long-term maternal outcomes were very rarely reported, with only 6.4% studies having measured urinary, and faecal incontinence each, and 5.5% having reported on breastfeeding complications.
      Planned mode of birth, for intention-to-treat analysis, or actual mode of birth was reported in 42.5% and 30.5% studies respectively. Induction of labour was also a frequently reported feature of labour, included in 30.5% studies. The frequency of the top three most reported outcomes in each category is listed in Table 2.
      Table 2Top three most commonly reported outcomes in each category.
      OutcomeTotalPSNCG
      Short-term neonatal
      APGAR score at 5 min84 (77.7%)1594614
      Perinatal mortality (includes intrapartum and/or neonatal only)73 (67.5%)243379
      Admission to NICU62 (57.4%)1372913
      Long-term neonatal
      Developmentally vulnerable/special needs/neurological morbidity20 (18.5%)33140
      Diagnosis of cerebral palsy11 (10.1%)5060
      Developmental delay or learning disability (incl. non-verbal cognition, social-emotional development, language deficiencies)11 (10.1%)2180
      Short-term maternal
      Maternal mortality23 (21.2%)53150
      PPH requiring blood transfusion16 (14.8%)3571
      Genital tract trauma16 (14.8%)14101
      Long-term maternal
      Urinary incontinence7 (6.4%)3130
      Faecal incontinence7 (6.4%)3130
      Breastfeeding complications6 (5.5%)3120
      Features of labour
      Vaginal Breech Birth101 (93.5%)12020069
      Elective caesarean83 (76.8%)7116059
      Emergency caesarean78 (72.2%)9127041
      Actual mode of birth46 (42.5%)7128010
      Planned mode of birth33 (30.5%)2113017
      Induction of labour33 (30.5%)102804
      P-primary; S-secondary; N-undesignated; C-part of composite; G-as a subject group.

      Methodological quality

      Out of 108 included articles, 32 (29.6%) scored 4 i.e., answered all four of the methodical assessment questions. However, 16 of these did not analyses any secondary outcomes or objectives. 17 (15.7%) scored 3, 45 (41.6%) scored 2, 6 (5.5%) scored 1, and 8 (7.4%) scored 0 with neither primary nor secondary objectives stated and defined. Table 3 shows detailed frequencies for each criterion. The primary objective was clearly stated in 47 (43.5%) of 108 included studies. 65 (60.1%) articles defined how the primary outcome was measured but did not explicitly classify it as a primary or secondary outcome. Notably, there was a discrepancy observed in definition and measurement for certain outcomes such as measurement period for perinatal death, or outcomes to include in a composite of trauma associated morbidity. For the former, there were 10 different time periods defined, while some left it undefined. Table 4 lists frequency for each of the definitions. 21 (22.2%) of included studies had clearly stated secondary objectives 26/108 (24.1%) studies had defined them. 58/108 (53.7%) did not investigate a secondary objective and did not have any secondary outcomes listed.
      Table 3Frequency of methodological assessment criteria.
      OutcomeStatedDefined
      PrimaryYes47Yes65
      No61No43
      SecondaryYes21Yes26
      No29No24
      N/a58N/a58
      Table 4Frequency of different definitions for perinatal mortality.
      Definition of outcomeFrequency
      Undefined35
      Within 28 days11
      Intrapartum or within 7 days7
      Intrapartum or within 28 days4
      Intrapartum or within 30 days3
      Within 7 days3
      Before discharge2
      Intrapartum or before discharge1
      Intrapartum or within 27 days (early 0–6/late 7–27)1
      Intrapartum stillbirth and undefined neonatal mortality1

      Meeting with PPI group

      The PPI group meeting was attended by service users, practicing midwives, health educators, and breech birth activists. Overall, the participants emphasised that neonatal risk outcomes should be provided during consultation, substantiated by robust statistics, particularly for commonly occurring negative outcomes. Women prioritised neonatal mortality as measured from the onset of labour, as they felt this would reflect a difference in risk compared to cephalic (head-first) birth, rather than with caesarean section. They emphasised the need for accurate statistics in taking informed decisions, particularly being able to compare risk of outcomes in vaginally born breech babies versus those born vaginally in a head-first position. There was an issue raised of health workers using hyper-clinical or very emotive language to describe possible negative outcomes. For example, several PPI members reported ‘head entrapment’ described as an outcome, and although the image was very emotive, they were unsure what the actual impact on their baby or themselves would have been had this occurred in their births.
      The time of clamping the baby’s umbilical cord was another common concern, and mothers agreed that the baby being taken away immediately was distressing, though no studies reported timing of umbilical cord clamping nor separation as outcomes. This was also true for admission to NICU, with mothers reporting that they needed to know why the baby had to go to the NICU, for how long, and if they themselves could join. There was agreement that features of labour outcomes such as rates and risks associated with induction, manoeuvres used etc. need to be more prominently reported in general. They also agreed on the importance of measuring long-term maternal outcomes particularly mental health effects for women and their partners, and rates and outcomes of future pregnancies. Service users stressed the need for improved psychological support available to women, to discuss the aftereffects of a possibly traumatic birth experience and feeling isolated during pregnancy. These concerns may also be important outcomes to measure.

      Discussion

      In designing a robust clinical trial, outcomes must be chosen carefully, reflecting clinical importance for service providers and meaningful endpoints for service users [
      • Williamson P.R.
      • et al.
      Developing core outcome sets for clinical trials: Issues to consider.
      ,
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ]. This systematic literature review has identified a comprehensive list of outcomes reported in current comparative studies of breech birth at term and assessed their variation and frequency; the first step of developing a Breech-COS.

      Summary of main findings and implications

      The results show that there is substantial inconsistency in the outcomes currently being reported. Mode of birth (vaginal breech birth, planned, and emergency CS) was the most commonly reported outcome. However, mode of birth is measured in almost every study as a subject group, i.e., to classify risks associated with each of the three modes of birth for breech presentation at term; this provided little information on the birth outcome based on intention-to-treat. Neonatal outcomes were more commonly reported than maternal ones: APGAR score, perinatal mortality, and admission to NICU; maternal mortality, PPH, and PPH requiring transfusion were reported most frequently in each of the categories respectively.
      Our results partially correspond with outcomes identified as ‘critical’ or ‘important’ in the recent NICE evidence review for breech presenting in labour, informing the guideline for Intrapartum care for women with existing medical conditions or obstetric complications and their babies [

      NICE Intrapartum care for women with existing medical conditions or obstetric complications and their babies. Evidence review for breech presenting in labour. NICE guideline [NG121] 2019 NICE

      ]. Concerning maternal outcomes, the evidence review identifies maternal mortality and major morbidities as critical, defined as obstetric anal sphincter injury (OASI), PPH and systemic infection. In our review, these were also the most common reported maternal outcomes. However, none of them was reported in over 25% of studies, and the heterogeneity with which they were measured would preclude meaningful comparisons. For example, studies reporting genital tract trauma seldom specifically reported rates of OASI, and the threshold for reporting PPH as an outcome differed considerably between studies. If a consensus agreement is reached that these, and similar major morbidities described for babies, are indeed critical to enable meaningful comparisons, agreement will also need to be reached on their definition and measurement.
      The results demonstrated a lack of consensus in the measurement period for perinatal mortality, also identified as ‘critical’ by NICE. Some studies measured deaths in the entire perinatal period (antepartum and intrapartum stillbirths and neonatal deaths) [
      • Bjellmo S.
      • et al.
      Is vaginal breech delivery associated with higher risk for perinatal death and cerebral palsy compared with vaginal cephalic birth? Registry-based cohort study in Norway.
      ], others only included the intrapartum and early neonatal period (within 7 days of life) [
      • Berhan Y.
      • Haileamlak A.
      The risks of planned vaginal breech delivery versus planned caesarean section for term breech birth: a meta-analysis including observational studies.
      ,
      • Vlemmix F.
      • et al.
      Term breech deliveries in the Netherlands: did the increased cesarean rate affect neonatal outcome? A population-based cohort study.
      ], while others still included the intrapartum and neonatal deaths within the first 28 days of life [
      • Vistad I.
      • Klungsøyr K.
      • Albrechtsen S.
      • Skjeldestad F.E.
      Neonatal outcome of singleton term breech deliveries in Norway from 1991 to 2011.
      ]. Often there was no clear definition of what time period was considered for neonatal death [
      • Bin Y.S.
      • Roberts C.L.
      • Ford J.B.
      • Nicholl M.C.
      Outcomes of breech birth by mode of delivery: a population linkage study.
      ,
      • Bleu G.
      • et al.
      Efficacité et sécurité du déclenchement du travail en cas de présentation du siège à terme.
      ]. This heterogeneity in reporting increases the likelihood of measurement inconsistency, inability to compare evidence, and can lead to research waste.
      Although not identified by NICE, APGAR score at 5 min is likely to be of clinical importance to service providers, as it is reflective of long-term cognitive outcomes for the baby such as reduced IQ [
      • Moore E.A.
      • et al.
      Birth outcomes and academic achievement in childhood: A population record linkage study.
      ] and scores less than 7 have been associated with neurological disability and low cognitive function in early adulthood [
      • Ehrenstein V.
      • et al.
      Association of Apgar score at five minutes with long-term neurologic disability and cognitive function in a prevalence study of Danish conscripts.
      ]. Measuring this outcome would be crucial in early detection of at-risk children and the consequent development of early intervention programs [
      • Razaz N.
      • et al.
      Five-minute Apgar score as a marker for developmental vulnerability at 5 years of age.
      ].
      The third commonly reported neonatal outcome, admission to NICU, is likely to have economic implications, increasing hospital and health service costs [
      • Merrit T.A.
      • Raddish M.
      A review of guidelines for the discharge of premature infants: opportunities for improving cost effectiveness - PubMed.
      ]. The importance of including this outcome is consistent with the findings of the PPI group meeting, where premature cord-clamping and admission to NICU were identified as a source of concern and distress for new mothers. The findings of this review are also concomitant with recent outcome sets developed in evaluating maternity care, where a 3-round Delphi study with key global stakeholders identified maternal death, mode of birth including use of instruments/manoeuvres, neonatal death, NICU admission, and PPH as the most important outcomes [
      • Devane D.
      • Begley C.M.
      • Clarke M.
      • Horey D.
      • Oboyle C.
      Evaluating maternity care: A core set of outcome measures.
      ].
      The results also showed that long-term maternal outcomes were very rarely reported (less than7%), particularly positive health focused, or salutogenic, outcomes. Where they were reported, most were measured by healthcare workers rather than patient-centred and self-reported. Participants in the PPI group expressed that their birth experience had long-term emotional effects, both positive and negative, and they would like more acknowledgement of these effects in research design. Long-term health outcomes and outcomes for subsequent pregnancies were also deemed important to service users, although these were less likely to be reported in current studies.
      Less than 30% of the included studies clearly defined and stated the primary and secondary (where relevant) objectives. Furthermore, there was an inconsistency in outcome definition and nomenclature. PPI group members stressed the importance of availability of robust risk outcome statistics and inclusion of outcomes related to features of labour such as manoeuvres used and long-term effects on women, particularly mental health related effects.

      Strengths and limitations

      Breech birth at term is an under-researched topic within maternal and child health, with no clinical trial published since 2000. Therefore, evidence synthesis depends heavily on the results of non-randomised observational cohort studies. To the best of our knowledge, there exists no published COS to investigate outcomes of breech birth at term [
      • Duffy J.
      • et al.
      Core outcome sets in women’s and newborn health: a systematic review.
      ]. This systematic review, and Breech-COS once developed, will bridge this gap in the literature, enable improved synthesis of evidence, and alleviate some of the methodological issues discussed above in comparing effectiveness studies on breech birth at term. This study design benefits from its inclusion and involvement of PPI members, ensuring that research findings are relevant and meaningful to service users.
      A strength of this review includes the comprehensive search criterion that yielded a wide-ranging list of outcomes. However, not all of these might be of clinical importance, and many might not be feasible to collect in a low-resource setting. Effectively combining, prioritising, and comparing these results in the future Delphi study, can help prevent unnecessary confusion and wasted resources [
      • Williamson P.R.
      • et al.
      Developing core outcome sets for clinical trials: Issues to consider.
      ]. The adapted methodological assessment design for this review allowed appraisal of outcomes but does not speak of limitations and inherent bias present in each of the included studies. Therefore, there is a risk of reporting bias present. In particular and most relevant to our work: outcome reporting bias which can be defined as selective reporting of some outcomes but not others, due to the influence of the results or statistical insignificance, which may compromise the validity of results [

      Higgins, J. et al., Cochrane Handbook for Systematic Reviews of Interventions. Cochrane Collaboration (Cochrane. Available from www.training.cochrane.org/handbook., 2019).

      ,
      • Williamson P.R.
      • et al.
      The COMET Handbook: Version 1.0.
      ].

      Conclusion

      This systematic review provides a comprehensive assessment of outcomes currently reported in effectiveness studies of breech birth at term. Data was extracted from 108 studies which yielded 211 outcomes in total. Heterogeneity in reported outcomes and lack of consensus in definition and specifics on measurement indicates a need to develop a COS in this field, in order to inform future effectiveness studies and the development of a trial protocol currently undergoing feasibility testing.

      Author’s contribution

      SW is the Chief Investigator; she conceived the study, led the proposal and protocol development. SW and TD wrote this manuscript. SW, TD, AH, and AR contributed to screening, data extraction and analysis. Professor Jane Sandall, Professor Andrew Shennan, Dr Catey Bunce and Phoebe Roberts (service user) contributed to study design and development of the proposal. All authors read and approved the final manuscript.

      Funding

      This study is funded by a National Institute of Health Research (NIHR300582) Advanced Fellowship and supported by the National Institute for Health Research (NIHR) Applied Research Collaboration South London (NIHR ARC South London) at King’s College Hospital NHS Foundation Trust. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care. The COS Delphi was registered with the King’s College London Research Ethics Office (MRA-18/19–13879). Study design and development, as well as data collection, management, analysis, interpretation, and writing of the report was conducted independent of the study sponsor and funder.

      Declaration of Competing Interest

      Shawn Walker, the lead author, is a co-Director of the Breech Birth Network, a community interest not-for-profit company.

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:

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