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Meta-Analysis
. 2018 Nov 9;11(11):CD008070.
doi: 10.1002/14651858.CD008070.pub4.

Maternal position in the second stage of labour for women with epidural anaesthesia

Affiliations
Meta-Analysis

Maternal position in the second stage of labour for women with epidural anaesthesia

Kate F Walker et al. Cochrane Database Syst Rev. .

Abstract

Background: Epidural analgesia in labour prolongs the second stage and increases instrumental delivery. It has been suggested that a more upright maternal position during all or part of the second stage may counteract these adverse effects. This is an update of a Cochrane Review published in 2017.

Objectives: To assess the effects of different birthing positions (upright or recumbent) during the second stage of labour, on maternal and fetal outcomes for women with epidural analgesia.

Search methods: We searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (5 June 2018), and the reference lists of retrieved studies.

Selection criteria: All randomised or quasi-randomised trials including pregnant women (primigravidae or multigravidae) in the second stage of induced or spontaneous labour receiving epidural analgesia of any kind. Cluster-randomised controlled trials would have been eligible for inclusion but we found none. Studies published in abstract form only were also eligible.We assumed the experimental intervention to be maternal use of any upright position during the second stage of labour, compared with the control condition of remaining in any recumbent position.

Data collection and analysis: Two review authors independently assessed trials for inclusion, assessed risks of bias, and extracted data. We contacted study authors to obtain missing data. We assessed the quality of the evidence using the GRADE approach.We carried out a planned sensitivity analysis of the three studies with low risks of bias for allocation concealment and incomplete outcome data reporting, and further excluded one study with a co-intervention (this was not prespecified).

Main results: We include eight randomised controlled trials, involving 4464 women, comparing upright positions versus recumbent positions in this update. Five were conducted in the UK, one in France and two in Spain.The largest UK trial accounted for three-quarters of all review participants, and we judged it to have low risk of bias. We assessed two other trials as being at low risk of selection and attrition bias. We rated four studies at unclear or high risk of bias for both selection and attrition bias and one study as high risk of bias due to a co-intervention. The trials varied in their comparators, with five studies comparing different positions (upright and recumbent), two comparing ambulation with (recumbent) non-ambulation, and one study comparing postural changes guided by a physiotherapist to a recumbent position.Overall, there may be little or no difference between upright and recumbent positions for our combined primary outcome of operative birth (caesarean or instrumental vaginal): average risk ratio (RR) 0.86, 95% confidence interval (CI) 0.70 to 1.07; 8 trials, 4316 women; I2 = 78%; low-quality evidence. It is uncertain whether the upright position has any impact on caesarean section (RR 0.94, 95% CI 0.61 to 1.46; 8 trials, 4316 women; I2 = 47%; very low-quality evidence), instrumental vaginal birth (RR 0.90, 95% CI 0.72 to 1.12; 8 trials, 4316 women; I2 = 69%) and the duration of the second stage of labour (mean difference (MD) 6.00 minutes, 95% CI -37.46 to 49.46; 3 trials, 456 women; I2 = 96%), because we rated the quality of the evidence as very low for these outcomes. Maternal position in the second stage of labour probably makes little or no difference to postpartum haemorrhage (PPH), (PPH requiring blood transfusion): RR 1.20, 95% CI 0.83 to 1.72; 1 trial, 3093 women; moderate-quality evidence. Maternal satisfaction with the overall childbirth experience was slightly lower in the upright group: RR 0.95, 95% CI 0.92 to 0.99; 1 trial, 2373 women. Fewer babies were born with low cord pH in the upright group: RR 0.43, 95% CI 0.20 to 0.90; 2 trials, 3159 infants; moderate-quality evidence.The results were less clear for other maternal or fetal outcomes, including trauma to the birth canal requiring suturing (average RR 1.00, 95% CI 0.89 to 1.13; 3 trials, 3266 women; I2 = 46%; low-quality evidence), abnormal fetal heart patterns requiring intervention (RR 1.69, 95% CI 0.32 to 8.84; 1 trial, 107 women; very low-quality evidence), or admission to neonatal intensive care unit (RR 0.54, 95% CI 0.02 to 12.73; 1 trial, 66 infants; very low-quality evidence). However, the CIs around some of these estimates were wide, and we cannot rule out clinically important effects.In our sensitivity analysis of studies at low risk of bias, upright positions increase the chance of women having an operative birth: RR 1.11, 95% CI 1.03 to 1.20; 3 trials, 3609 women; high-quality evidence. In absolute terms, this equates to 63 more operative births per 1000 women (from 17 more to 115 more). This increase appears to be due to the increase in caesarean section in the upright group (RR 1.29; 95% CI 1.05 to 1.57; 3 trials, 3609 women; high-quality evidence), which equates to 25 more caesarean sections per 1000 women (from 4 more to 49 more). In the sensitivity analysis there was no clear impact on instrumental vaginal births: RR 1.08, 95% CI 0.91 to 1.30; 3 trials, 3609 women; low-quality evidence.

Authors' conclusions: There may be little or no difference in operative birth between women who adopt recumbent or supine positions during the second stage of labour with an epidural analgesia. However, the studies are heterogeneous, probably related to differing study designs and interventions, differing adherence to the allocated intervention and possible selection and attrition bias. Sensitivity analysis of studies at low risk of bias indicated that recumbent positions may reduce the need for operative birth and caesarean section, without increasing instrumental delivery. Mothers may be more satisfied with their experience of childbirth by adopting a recumbent position. The studies in this review looked at left or right lateral and semi-recumbent positions. Recumbent positions such as flat on the back or lithotomy are not generally used due to the possibility of aorto-caval compression, although we acknowledge that these recumbent positions were not the focus of trials included in this review.

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Conflict of interest statement

Kate F Walker: none known Marion Kibuka: none known Jim G Thornton: none known Nia W Jones: none known

Figures

1
1
Study flow diagram.
2
2
Risk of bias summary: review authors' judgements about each risk of bias item for each included study
3
3
Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies.
1.1
1.1. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 1 Operative birth (caesarean or instrumental vaginal).
1.2
1.2. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 2 Duration of second stage labour (minutes) (from time of randomisation to birth).
1.3
1.3. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 3 Caesarean section.
1.4
1.4. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 4 Instrumental vaginal birth.
1.5
1.5. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 5 Trauma to birth canal requiring suturing.
1.6
1.6. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 6 Blood loss (greater than 500 mL) (trial authors defined it as PPH requiring blood transfusion).
1.7
1.7. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 7 Prolonged second stage, defined as pushing for more than 60 minutes (trial authors report 'duration of pushing phase' in minutes.
1.8
1.8. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 8 Maternal experience and satisfaction of labour.
1.9
1.9. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 9 Abnormal fetal heart rate patterns, requiring intervention.
1.10
1.10. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 10 Apgar score less than seven at five minutes.
1.11
1.11. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 11 Apgar score less than four at five minutes.
1.12
1.12. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 12 Low cord pH.
1.13
1.13. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 13 Admission to neonatal intensive care unit.
1.14
1.14. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 14 Need for ventilation (trial authors report 'intubation').
1.15
1.15. Analysis
Comparison 1 Upright position versus recumbent position, Outcome 15 Perinatal death.
2.1
2.1. Analysis
Comparison 2 Upright position versus recumbent position (sensitivity analyses ‐ high‐quality studies only), Outcome 1 Operative birth (caesarean or instrumental vaginal).
2.2
2.2. Analysis
Comparison 2 Upright position versus recumbent position (sensitivity analyses ‐ high‐quality studies only), Outcome 2 Caesarean section.
2.3
2.3. Analysis
Comparison 2 Upright position versus recumbent position (sensitivity analyses ‐ high‐quality studies only), Outcome 3 Instrumental vaginal birth.

Update of

References

References to studies included in this review

Boyle 2001 {published data only}
    1. Boyle S, Entwistle F, Hamilton C, Kulinska E. A randomised controlled trial examining the effect of ambulation on labour outcome who choose a combined spinal epidural for pain relief in labour. International Confederation of Midwives. Midwives and women working together for the family of the world: ICM Proceedings; 2002; Vienna, Austria. 2002:1‐11.
BUMPES 2017 {published data only}
    1. Bick D, Briley A, Brocklehurst P, Eddama O, Hardy P, Juszczak E, et al. A multicentre, randomised controlled trial of position during the late stages of labour in women with an epidural – (BUMPES). BJOG: an International Journal of Obstetrics and Gynaecology 2016;123(Suppl 2):61.
    1. Bick D, Briley A, Brocklehurst P, Hardy P, Juszczak E, Rivero‐Arias O, et al. A multicentre, randomised controlled trial of position during the late stages of labour in nulliparous women with an epidural: clinical effectiveness and an economic evaluation (BUMPES). Health Technology Assessment 2017;21(65):1‐175. - PMC - PubMed
    1. Brocklehurst P. Upright maternal position in second stage labour in women with epidural analgesia; a randomised controlled trial. www.hta.ac.uk (accessed 27 January 2010).
    1. Brocklehurst P, MacArthur C, Moore P, Wilson M, Bick D, Briley A, et al. A multicentre, randomised controlled trial of position during the late stages of labour in women with an epidural (BUMPES). BJOG: an International Journal of Obstetrics and Gynaecology 2016;123(Suppl 1):11.
    1. Brocklehurst P, MacArthur C, Moore P, Wilson M, Bick D, Briley A, et al. A multicentre, randomised controlled trial of position during the late stages of labour in women with an epidural‐(bumpes). BJOG: an international journal of obstetrics and gynaecology 2016;123(Suppl 2):61.
Downe 2004 {published data only}
    1. Downe S, Gerrett D, Renfrew MJ. A prospective randomised trial on the effect of position in the passive second stage of labour on birth outcome in nulliparous women using epidural analgesia. Midwifery 2004;20(2):157‐68. - PubMed
Golara 2002 {published data only}
    1. Golara M, Shennan AH. Upright versus recumbent position in the second stage of labour in women with combined spinal‐epidural analgesia. International Journal of Obstetric Anesthesia 2002;11(1):19‐22. - PubMed
    1. Plaat F, Golara M, Shennan A. Upright vs recumbent position with mobile extradurals in the early second stage of labour. British Journal of Anaesthesia 1996;76:102.
Karraz 2003 {published data only}
    1. Karraz MA. Ambulatory epidural anesthesia and the duration of labor. International Journal of Gynecology & Obstetrics 2003;80(2):117‐22. - PubMed
Simarro 2017 {published data only}
    1. Simarro M, Espinosa JA, Salinas C, Ojea R, Salvadores P, Walker C, et al. A prospective randomized trial of postural changes vs passive supine lying during the second stage of labor under epidural analgesia. Medical Sciences (Basel, Switzerland) 2017; Vol. 5, issue 1:pii; E5. - PMC - PubMed
    1. Simarro M, Walker C, Salinas C, Martinez A, Henriquez A, Garcia G, et al. Effects of postural changes during the second stage of labor among women with epidural analgesia. International Urogynecology Journal and Pelvic Floor Dysfunction 2011;22(Suppl 1):S13‐S14.
Theron 2011 {published data only}
    1. Theron A, Baraz R, Thorp‐Jones D, Sanders J, Collis R. Does position in the passive second stage of labour affect birth outcome in nulliparous women using epidural analgesia. International Journal of Obstetric Anesthesia 2011;20(Suppl 1):S12.
Walker 2012 {published data only}
    1. Walker C, Rodriguez T, Herranz A, Espinosa JA, Sanchez E, Espuna‐Pons M. Alternative model of birth to reduce the risk of assisted vaginal delivery and perineal trauma. International Urogynecology Journal 2012;23(9):1249‐56. - PubMed
    1. Walker C, Rodriguez T, Herranz A, Garcia IM, Espinosa JA, Sanchez E, et al. Second stage of labor with postural change and lateral position in women with epidural analgesia: a randomized controlled trial. International Urogynecology Journal and Pelvic Floor Dysfunction 2011;22(Suppl 1):S11‐S12.

References to studies excluded from this review

Amiri 2012 {published data only}
    1. Amiri L, Shirazi V, Rajabalipoor F. The effects of different positioning on the duration of the second stage of labor in primiparous women. Journal of Zanjan University of Medical Sciences and Health Services 2012;20(80):105‐14.
Asselineau 1996 {published data only}
    1. Asselineau D. Does ambulation under epidural analgesia during labor modify the conditions of fetal extraction? [La deambulation sous peridurale lors du travail modifie‐t‐elle les conditions d'extraction foetale?]. Contraception, Fertilité, Sexualité 1996;24(6):505‐8. - PubMed
Collis 1999 {published data only}
    1. Collis R, Harding S, Morgan B. Effect of maternal ambulation on labour with low‐dose combined spinal‐epidural analgesia. Anaesthesia 1999;54(6):535‐9. - PubMed
Danilenko‐Dixon 1996 {published data only}
    1. Danilenko‐Dixon DR, Tefft L, Cohen RA, Haydon B, Carpenter MW. Positional effects on maternal cardiac output during labor with epidural analgesia. American Journal of Obstetrics and Gynecology 1996;175(4 Pt 1):867‐72. - PubMed
Hofmeyr 2018 {published data only}
    1. Hofmeyr GJ, Singata M, Lawrie T, Vogel JP, Landoulsi S, Seuc AH, et al. A multicentre randomized controlled trial of gentle assisted pushing in the upright posture (GAP) or upright posture alone compared with routine practice to reduce prolonged second stage of labour (the Gentle Assisted Pushing study): study protocol. Reproductive Health 2015;12(1):114. - PMC - PubMed
    1. Hofmeyr GJ, Vogel JP, Singata M, Abu Habib N, Landoulsi S, Gülmezoglu AM. A multicentre, three‐arm, randomized, open‐label clinical trial of gentle assisted pushing in the upright position, upright position alone or routine practice to reduce prolonged second stage of labour. BMJ (in press).
    1. PACTR201502001034448. The Gentle Assisted Pushing Study: a multicentre randomized controlled trial of gentle assisted pushing in the upright posture (GAP) or upright posture alone compared with routine practice to reduce prolonged second stage of labour. pactr.org/ATMWeb/appmanager/atm/atmregistry?dar=true&tNo=PACTR201502... (first received 13 February 2015). - PMC - PubMed
Martin 2011 {published data only}
    1. Martin de Vega RA, Feijoo Iglesias MB, Magdaleno del Rey G, Rodriguez Ferrer RM, Ruiz Rey AM. Effect of SIMS modified posture on the rotation and descent of the fetus in women during their first delivery with epidural analgesia. Nure Investigacion 2011;55:1‐11.
Thies‐Lagergren 2011 {published data only}
    1. Thies‐Lagergren L, Kvist LJ, Christensson K, Hildingsson I. No reduction in instrumental vaginal births and no increased risk for adverse perineal outcome in nulliparous women giving birth on a seat: results of a Swedish randomized controlled trial. BMC Pregnancy and Childbirth 2011;11:22. - PMC - PubMed
Zaibunnisa 2015 {published data only}
    1. Zaibunnisa, Ara F, Ara B, Kaker P, Aslam M. Comparison of complications between lithotomy position and squatting position during childbirth. Professional Medical Journal 2015;22(4):390‐4.

Additional references

Anim‐Somuah 2005
    1. Anim‐Somuah M, Smyth RMD, Jones L. Epidural versus non‐epidural or no analgesia in labour. Cochrane Database of Systematic Reviews 2005, Issue 4. [DOI: 10.1002/14651858.CD000331.pub2] - DOI - PubMed
Anim‐Somuah 2018
    1. Anim‐Somuah M, Smyth RMD, Cyna AM, Cuthbert A. Epidural versus non‐epidural or no analgesia for pain management in labour. Cochrane Database of Systematic Reviews 2018, Issue 5. [DOI: 10.1002/14651858.CD000331.pub4] - DOI - PMC - PubMed
Bodner‐Adler 2003
    1. Bodner‐Adler B, Bodner K, Kimberger O, Lozanov P, Husslein P, Mayerhofer K. Women's position during labour: influence on maternal and neonatal outcome. Wiener Klinische Wochenschrift 2003;115(19‐20):720‐3. - PubMed
Borell 1957
    1. Borell V, Fernstrom I. A pelvimetric method for the assessment of pelvic mouldability. Acta Radiologica 1957;47(5):365‐70. - PubMed
Chen 1987
    1. Chen SZ, Aisaka K, Mori H, Kigawa T. Effects of sitting position on uterine activity during labor. Obstetrics and Gynecology 1987;69(1):67‐73. - PubMed
COMET 2001
    1. Comparative Obstetric Mobile Epidural Trial (COMET) Study Group UK. Effect of low‐dose mobile versus traditional epidural techniques on mode of delivery: a randomised controlled trial. Lancet 2001;358(9275):19‐23. - PubMed
De Jonge 2004
    1. Jonge A, Teunissen TA, Lagro‐Janssen AL. Supine position compared to other positions during the second stage of labor: a meta‐analytic review. Journal of Psychosomatic Obstetrics and Gynaecology 2004;25(1):35‐45. - PubMed
Deeks 2011
    1. Deeks JJ, Higgins JP, Altman DG, editor(s). Chapter 9: Analysing data and undertaking meta‐analyses. In: Higgins JP, Green S, editor(s). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from handbook.cochrane.org.
Flynn 1978
    1. Flynn AM, Kelly J, Hollins G, Lynch PF. Ambulation in labour. British Medical Journal 1978;2(6137):591‐3. - PMC - PubMed
Gardosi 1989
    1. Gardosi J, Hutson N, B‐Lynch C. Randomised, controlled trial of squatting in the second stage of labour. Lancet 1989; Vol. 2, issue 8654:74‐7. - PubMed
Goodfellow 1983
    1. Goodfellow CF, Hull MG, Swaab DF, Dogterom J, Buijs RM. Oxytocin deficiency at delivery with epidural analgesia. British Journal of Obstetrics and Gynaecology 1983;90(3):214‐9. - PubMed
Gupta 2017
    1. Gupta JK, Sood A, Hofmeyr GJ, Vogel JP. Position in the second stage of labour for women without epidural anaesthesia. Cochrane Database of Systematic Reviews 2017, Issue 5. [DOI: 10.1002/14651858.CD002006.pub4] - DOI - PMC - PubMed
Higgins 2003
    1. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta‐analyses. BMJ 2003;327(7414):557‐60. - PMC - PubMed
Higgins 2011a
    1. Higgins JP, Altman DG, Sterne JA, editor(s). Chapter 8: Assessing risk of bias in included studies. In: Higgins JP, Green S, editor(s). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from handbook.cochrane.org.
Higgins 2011b
    1. Higgins JP, Deeks JJ, Altman DG, editor(s). Chapter 16: Special topics in statistics. In: Higgins JP, Green S, editor(s), Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from handbook.cochrane.org.
Jones 2012
    1. Jones L, Othman M, Dowswell T, Alfirevic Z, Gates S, Newburn M, et al. Pain management for women in labour: an overview of systematic reviews. Cochrane Database of Systematic Reviews 2012, Issue 3. [DOI: 10.1002/14651858.CD009234.pub2] - DOI - PMC - PubMed
Lawrence 2013
    1. Lawrence A, Lewis L, Hofmeyr GJ, Styles C. Maternal positions and mobility during first stage labour. Cochrane Database of Systematic Reviews 2013, Issue 10. [DOI: 10.1002/14651858.CD003934.pub4] - DOI - PMC - PubMed
Lieberman 2005
    1. Lieberman E, Davidson K, Lee‐Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural analgesia. Obstetrics and Gynecology 2005;105(5 Pt 1):974‐82. - PubMed
Liebling 2004
    1. Liebling RE, Swingler R, Patel RR, Verity L, Soothill PW, Murphy DJ. Pelvic floor morbidity up to one year after difficult instrumental delivery and cesarean section in the second stage of labor: a cohort study. American Journal of Obstetrics and Gynecology 2004;191(1):4‐10. - PubMed
MacLennan 2000
    1. MacLennan AH, Taylor AW, Wilson DH, Wilson D. The prevalence of pelvic floor disorders and their relationship to gender, age, parity and mode of delivery. BJOG: an international journal of obstetrics and gynaecology 2000;107(12):1460‐70. - PubMed
Martino 2007
    1. Martino V, Iliceto N, Simeoni U. Occipito‐posterior fetal head position, maternal and neonatal outcome. Minerva Ginecologica 2007;59(4):459‐64. - PubMed
Méndez‐Bauer 1975
    1. Méndez‐Bauer C, Arroyo J, García Ramos C, Menéndez A, Lavilla M, Izquierdo F, et al. Effects of standing position on spontaneous uterine contractility and other aspects of labor. Journal of Perinatal Medicine 1975;3(2):89‐100. - PubMed
O'Driscoll 2003
    1. O'Driscoll K, Meagher D, Robson, M. Active Management of Labour. Elsevier Health Sciences, 2003.
Prabhu 2009
    1. Prabhu A, Plaat F. Regional analgesia for labour: a survey of UK practice. International. Journal of Obstetric Anesthesia 2009;18(Suppl 1):S28.
Rahm 2002
    1. Rahm VA, Hallgren A, Högberg H, Hurtig I, Odlind V. Plasma oxytocin levels in women during labor with or without epidural analgesia: a prospective study. Acta Obstetricia et Gynecologica Scandinavica 2002;81(11):1033‐9. - PubMed
RevMan 2014 [Computer program]
    1. The Nordic Cochrane Centre, The Cochrane Collaboration. Review Manager 5 (RevMan 5). Version 5.3. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014.
Richardson 2007
    1. Richardson A, Mmata C. NHS Maternity Statistics, England: 2005‐2006. NHS Infomation Centre, 2007.
Sterne 2011
    1. Sterne JA, Egger M, Moher D, editor(s). Chapter 10: Addressing reporting biases. In: Higgins JP, Green S, editor(s). Cochrane Handbook for Systematic Reviews of Intervention. Version 5.1.0 (updated March 2011). The Cochrane Collaboration, 2011. Available from handbook.cochrane.org.
Watson 1994
    1. Watson V. The duration of the second stage of labour. Modern Midwife 1994;4(6):21‐2. - PubMed
Wong 2015
    1. Wong E, Poonawala Y. Spinal dosing for labour combined spinal epidural. International Journal of Obstetric Anesthesia 2015;24(Suppl 1):s29.

References to other published versions of this review

Kemp 2013
    1. Kemp E, Kingswood CJ, Kibuka M, Thornton JG. Position in the second stage of labour for women with epidural anaesthesia. Cochrane Database of Systematic Reviews 2013, Issue 1. [DOI: 10.1002/14651858.CD008070.pub2] - DOI - PubMed
Kibuka 2017
    1. Kibuka M, Thornton JG. Position in the second stage of labour for women with epidural anaesthesia. Cochrane Database of Systematic Reviews 2017, Issue 2. [DOI: 10.1002/14651858.CD008070.pub3] - DOI - PMC - PubMed

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