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Comparison of continuous infusion versus midwife administered top-ups of epidural bupivacaine for labour analgesia: effect on second stage of labour and mode of delivery
International Journal of Obstetric Anesthesia (2003) 12, 9–11 Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0959-289X(02)00158-9
ORIGINAL ARTICLE
Comparison of continuous infusion versus midwife administered top-ups of epidural bupivacaine for labour analgesia: effect on second stage of labour and mode of delivery T. S. Usha Kiran,a M. B. Thakur,b J. A. Bethel,c P. S. Bhal,a R. E. Collisb a
Department of Obstetrics & Gynaecology, University Hospital of Wales, Cardiff, UK; bDepartment of Anaesthetics, University Hospital of Wales, Cardiff, UK; cUniversity of Wales College of Medicine, Cardiff, UK
SUMMARY. Using a population-based study we retrospectively compared the effect of continuous versus intermittent top-up epidural analgesia on the outcome of labour at the University Hospital of Wales. We analysed the labour outcome of 410 primigravid deliveries over an 18-month period during a change in delivery suite protocol. Data were retrieved from the Cardiff Births Survey and the sample was analysed in two groups: group 1 (n ¼ 201) received a continuous infusion of 0.1% bupivacaine plus fentanyl 2 lg/mL and group 2 (n ¼ 209) received intermittent top-ups of the same solution. Outcome measures were the number of operative deliveries and the proportion of those deliveries that were due to prolongation of the second stage of labour. There were no significant differences in terms of group characteristics, women undergoing assisted vaginal delivery (group 1: 83 vs. group 2: 70, OR 0.8 CI 0.5– 1.2), caesarean section (group 1: 59 vs. group 2: 61, OR 1.0 CI 0.6–1.5), and women with prolonged second stage (group 1: 50 vs. group 2: 47, OR 1.1 CI 0.6–1.8). The presumed reduction in motor blockade associated with intermittent top-up epidural regimes did not affect the outcome of labour. Ó 2002 Elsevier Science Ltd. All rights reserved.
up epidural regime where both used 0.1% bupivacaine plus fentanyl 2 lg/mL, the hypothesis being that there might have been a reduction in obstetric intervention, and in particular, a reduction in delay in the second stage of labour, when our unit changed from a continuous infusion to a top-up to maintain analgesia in labour, because of the recognised reduction in bupivacaine usage associated with the second technique.
INTRODUCTION A survey conducted in 1999 showed that 90% of units in the UK offered a 24-h epidural service with an average epidural rate of 24%.1 Although the efficacy of epidural bupivacaine in terms of analgesia is well known, traditional or higher dose epidural analgesia increases the length of the second stage of labour and the number of instrumental deliveries.2;3 Efforts to reduce the total dose of local anaesthetic and hence the motor blockade have been advocated in an attempt to improve the obstetric outcome.4–7 The aim of this audit was to compare a continuous epidural infusion with an intermittent top-
MATERIALS AND METHODS This was a population-based study. Data were retrieved from the Cardiff Births Survey, which included residents of the South Glamorgan area, where all births have been documented since 1965. The study period was from 1st March, 1998 to 30th December, 1999. The delivery suite practice changed from continuous infusions to midwife administered top-ups to maintain analgesia in labour, both containing the same solution of bupivacaine 0.1% and fentanyl 2 lg/mL, during this period. There were approximately three months during the change over when there was an overlap of the two techniques. A period of four months (giving a wider margin to obtain
Accepted April 2002 T. S. Usha Kiran, Specialist registrar, Department of Obstetrics & Gynaecology; Milind B. Thakur, Senior house officer, Department of Anaesthetics; Jackie A. Bethel, Clinical data manager, University of Wales College of Medicine; P. S. Bhal, Consultant, Department of Obstetrics & Gynaecology; R. E. Collis, Consultant, Department of Anaesthetics, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, UK. Correspondence to: 66 Cefn Graig, Rhwibina, Cardiff CF14 6SX, UK. Tel: +44-292-065-0981; E-mail: [email protected] 9
10 International Journal of Obstetric Anesthesia accurate data) was omitted in order to avoid this overlap. There were no changes in obstetric or anaesthetic consultants or in labour management protocols during this period. The study sample contained only uncomplicated, low risk primigravid women with a single fetus in cephalic presentation; all had received epidural analgesia for labour. Exclusion criteria were any pregnancy with the following factors: gestation of less than 37 weeks, medical disorders (e.g., heart disease, renal disease, diabetes, pre-existing hypertension, and asthma), surgical disorders and obstetric complications (e.g., antepartum haemorrhage, pregnancy-induced hypertension, and preeclampsia). Data collected included maternal age, body mass index, duration of second stage of labour, mode of delivery, birth weight of the baby and Apgar scores. Mode of delivery was our primary outcome measure. Secondary outcome measures were duration of second stage of labour and fetal well-being. Prolonged second stage was defined as more than 3 h of full dilatation, as it is our delivery suite practice to intervene at this stage. Our routine practice for women in labour includes vaginal examinations every 2–3 h (depending on the strength of contractions) until 8 cm dilatation and hourly thereafter until full dilatation. Statistical analysis Data were analysed using SPSS Version 10. Non-parametric tests were used. Categorical data were expressed as proportions, comparisons were made using v2 test and risk was expressed as odds ratio with 95% confidence intervals. Maternal age, body mass index and birth weight of the baby were compared using Mann–Whitney U test. A P value of <0.05 was considered significant. Logistic regression was used to assess independent risk factors for instrumental delivery.
RESULTS The sample number in each group after strict application of inclusion and exclusion criteria was comparable (n ¼ 201 vs. n ¼ 209). Both the groups were similar in
Table 1. Characteristics of the sample groups. Median (range)
Sample characteristics Maternal age (years) Body mass index (kg m2 ) Birth weight (g) Gestational age (weeks)
Group 1 (Continuous infusion) (n ¼ 201)
Group 2 (Intermittent top-ups) (n ¼ 209)
28 (16–45) 27.8 (15–44) 23.8 (16–43) 23.7 (14–42) 3450 (2060–4450) 3440 (2450–4590) 40 (37–42) 40 (37–42)
Mann–Whitney test: there were no significant differences between the groups.
age, body mass index, gestational age, and birth weight (Table 1). Although there appeared to be an increased number of women with assisted vaginal delivery and prolonged second stage of labour in the group that received continuous infusion compared to those who had intermittent top-ups, these differences were not statistically significant (Table 2). There were also no significant differences in the caesarean section rate or Apgar scores (Table 2). Using logistic regression with instrumental delivery as the outcome, the only independent factors affecting outcome were maternal age (OR 1.09, CI 1.05–1.13) and the birth weight of the baby (OR 1.001, CI 1.000– 1.001). Older women with larger babies were at a higher risk of assisted vaginal delivery irrespective of whether they had received continuous or intermittent top-ups of epidural analgesia during labour. DISCUSSION Despite auditing a reasonable number of records, we were unable to demonstrate any significant differences in the outcome of labour between our two groups. The presumed decrease in motor blockade between the two techniques used for labour analgesia did not significantly alter the proportion of women with a prolonged second stage of labour and the number of operative vaginal or caesarean deliveries. Studies that have examined local anaesthetic use prospectively have shown a reduction in the total local
Table 2. Outcome of labour
Labour outcome Mode of delivery Spontaneous vaginal Instrumental Caesarean section Second stage >180 min Apgar score below 7 1 min 5 min
Group 1 (Continuous infusion) (n ¼ 201) 59 83 59 50
(29.4%) (41.3%) (29.4%) (31.6%)
21 (10.5%) 4 (2%)
Group 2 (Intermittent top-ups) (n ¼ 209) 70 78 61 47
(33.5%) (37.3%) (29.2%) (29.2%)
19 (9.1%) 3 (1.4%)
Odds ratio (95% Confidence interval)
0.8 1.2 1.0 1.1
(0.5–1.2) (0.7–2.0) (0.6–1.5) (0.6–1.8)
0.8 (0.4–1.6) 0.7 (0.1–3.2)
Continuous infusion versus midwife top-ups for labour analgesia 11 anaesthetic dose required to maintain labour analgesia, with intermittent top ups as opposed to continuous infusions of the same solution.6–8 Although this method of reducing the local anaesthetic dose has led to decreased motor blockade, benefits regarding obstetric outcome have not been consistent. Some authors have reported a decrease in the instrumental delivery rate,6;9 especially when high dose and low dose top-ups are compared. When low dose epidural solutions are compared using different delivery systems, the difference in motor block has presumably been smaller than with any high dose regimes and there has been no differences in outcome of labour.8;9 We assumed in this study that the mothers experienced a reduction in motor block over these two time periods. This assumption is based on the many prospective studies comparing top-ups and infusions of the same solution and the reports from the midwives looking after the mothers (personal communication) who noticed that many mothers were much more mobile than before the change of practice. We accept that this is not objective evidence and there is a possibility of bias. Although motor block is commonly assessed in terms of the motherÕs ability to move her legs, there has never been a study that examined the effect of these different epidural regimes on perineal analgesia or pelvic floor tone. Neither reduced motor blockade,4 nor ambulation10;11 among those with little motor block, appear per se to improve obstetric outcome. There are obstetric differences, such as degree of extension and position of the fetal head, shape of the maternal pelvis, strength of contractions, age of the mother and size of the baby, which might contribute to the final obstetric outcome. Furthermore, it is possible that women with some of these unfavourable factors are motivated by the midwifery and medical staff to opt for epidural analgesia, with anticipation for its requirement at a later stage. Similar findings were suggested by Yancey et al.12 This may mean that we are dealing with a group of women in whom a delay in second stage of labour and operative delivery rate is going to be higher anyway than the nonepidural group, and by simply reducing motor blockade further in these mothers, it is unlikely that there would be a major impact on operative delivery rates. We noted that increasing maternal age and birth weight were independent risk factors for operative vaginal delivery. Studies have reported that older mothers and those with large babies are at a higher risk of operative vaginal delivery.13–14 Although we recognise that the retrospective nature of this study poses limitations, as it was not possible to
obtain information on the amount of bupivacaine used, the density of motor blockade, quality of analgesia and maternal satisfaction, there seems to be growing evidence that reducing motor block further does not change the outcome of labour. Changing epidurals from high dose to low dose bupivacaine with an opioid seems to reduce obstetric intervention, but the high intervention rate in both our groups of mothers reflects either an aspect of the block that is unchanged (such as perineal analgesia/motor block) or obstetric risk factors that we can not influence.
REFERENCES 1. Burnstein R, Buckland R, Pickett J A. A survey of epidural analgesia for labour in the United Kingdom. Anaesthesia 1999; 54: 634–640. 2. Howell CJ, Epidural versus non-epidural analgesia for pain relief in labour (Cochrane Review). In: The Cochrane Library, 2nd ed. Update Software: Oxford. 3. Echt M, Begneaud W, Montgomery D. Effect of epidural analgesia on the primary caesarean section and forceps delivery rates. J Reprod Med 2000; 45: 557–561. 4. Russell R, Reynolds F. Epidural infusion of low-dose bupivacaine and opioid in labour. Does reducing motor block increase the spontaneous delivery rate? Anaesthesia 1996; 51: 266–273. 5. Collis R E, Baxandall M L, Srikantharajah I D, Edge G, Kadim M Y, Morgan B M. Combined spinal epidural (CSE) analgesia technique, management and outcome of 300 mothers. International Journal Obstetric Anesthesia 1994; 3: 75–81. 6. Smedstad K G, Morison D H. A comparative study of continuous and intermittent epidural analgesia for labour and delivery. Can J Anaesth 1988; 35: 234–241. 7. Collis R E, Plaat F S, Morgan B M. Comparison of midwife top-ups; continuous infusion and patient controlled epidural analgesia for maintaining mobility after a low-dose combined spinal–epidural. Br J Anaesth 1999; 82: 233–236. 8. Purdie J, Reid J, Thorburn J, Asbury A J. Continuous extradural analgesia: comparison of midwife top-ups, continuous infusions and patient controlled administration. Br J Anaesth 1992; 68: 580–584. 9. 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: 19–23. 10. Collis R E, Harding S A, Morgan B M. Effect of maternal ambulation on labour with low-dose combined spinal epidural analgesia. Anaesthesia 1999; 54: 535–539. 11. Bloom S L, McIntire D D, Kelly M A, et al. Lack of effect of walking on labor and delivery. N Engl J Med 1998; 339: 76–79. 12. Yancey M K, Pierce B, Schweitzer D, Daniels D. Observations on labor epidural analgesia and operative delivery rates. Am J Obstet Gynecol 1999; 180: 353–359. 13. Bahar A M. Risk factors and fetal outcome in cases of shoulder dystocia compared with normal deliveries of a similar birth weight. Br J Obstet Gynaecol 1996; 103: 868–872. 14. Ezra Y, McParland P, Farine D. High delivery intervention rates in nulliparous women over age 35. Eur J Obstet Gynecol Reprod Biol 1995; 62: 203–207.
ORIGINAL ARTICLE
Comparison of continuous infusion versus midwife administered top-ups of epidural bupivacaine for labour analgesia: effect on second stage of labour and mode of delivery T. S. Usha Kiran,a M. B. Thakur,b J. A. Bethel,c P. S. Bhal,a R. E. Collisb a
Department of Obstetrics & Gynaecology, University Hospital of Wales, Cardiff, UK; bDepartment of Anaesthetics, University Hospital of Wales, Cardiff, UK; cUniversity of Wales College of Medicine, Cardiff, UK
SUMMARY. Using a population-based study we retrospectively compared the effect of continuous versus intermittent top-up epidural analgesia on the outcome of labour at the University Hospital of Wales. We analysed the labour outcome of 410 primigravid deliveries over an 18-month period during a change in delivery suite protocol. Data were retrieved from the Cardiff Births Survey and the sample was analysed in two groups: group 1 (n ¼ 201) received a continuous infusion of 0.1% bupivacaine plus fentanyl 2 lg/mL and group 2 (n ¼ 209) received intermittent top-ups of the same solution. Outcome measures were the number of operative deliveries and the proportion of those deliveries that were due to prolongation of the second stage of labour. There were no significant differences in terms of group characteristics, women undergoing assisted vaginal delivery (group 1: 83 vs. group 2: 70, OR 0.8 CI 0.5– 1.2), caesarean section (group 1: 59 vs. group 2: 61, OR 1.0 CI 0.6–1.5), and women with prolonged second stage (group 1: 50 vs. group 2: 47, OR 1.1 CI 0.6–1.8). The presumed reduction in motor blockade associated with intermittent top-up epidural regimes did not affect the outcome of labour. Ó 2002 Elsevier Science Ltd. All rights reserved.
up epidural regime where both used 0.1% bupivacaine plus fentanyl 2 lg/mL, the hypothesis being that there might have been a reduction in obstetric intervention, and in particular, a reduction in delay in the second stage of labour, when our unit changed from a continuous infusion to a top-up to maintain analgesia in labour, because of the recognised reduction in bupivacaine usage associated with the second technique.
INTRODUCTION A survey conducted in 1999 showed that 90% of units in the UK offered a 24-h epidural service with an average epidural rate of 24%.1 Although the efficacy of epidural bupivacaine in terms of analgesia is well known, traditional or higher dose epidural analgesia increases the length of the second stage of labour and the number of instrumental deliveries.2;3 Efforts to reduce the total dose of local anaesthetic and hence the motor blockade have been advocated in an attempt to improve the obstetric outcome.4–7 The aim of this audit was to compare a continuous epidural infusion with an intermittent top-
MATERIALS AND METHODS This was a population-based study. Data were retrieved from the Cardiff Births Survey, which included residents of the South Glamorgan area, where all births have been documented since 1965. The study period was from 1st March, 1998 to 30th December, 1999. The delivery suite practice changed from continuous infusions to midwife administered top-ups to maintain analgesia in labour, both containing the same solution of bupivacaine 0.1% and fentanyl 2 lg/mL, during this period. There were approximately three months during the change over when there was an overlap of the two techniques. A period of four months (giving a wider margin to obtain
Accepted April 2002 T. S. Usha Kiran, Specialist registrar, Department of Obstetrics & Gynaecology; Milind B. Thakur, Senior house officer, Department of Anaesthetics; Jackie A. Bethel, Clinical data manager, University of Wales College of Medicine; P. S. Bhal, Consultant, Department of Obstetrics & Gynaecology; R. E. Collis, Consultant, Department of Anaesthetics, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, UK. Correspondence to: 66 Cefn Graig, Rhwibina, Cardiff CF14 6SX, UK. Tel: +44-292-065-0981; E-mail: [email protected] 9
10 International Journal of Obstetric Anesthesia accurate data) was omitted in order to avoid this overlap. There were no changes in obstetric or anaesthetic consultants or in labour management protocols during this period. The study sample contained only uncomplicated, low risk primigravid women with a single fetus in cephalic presentation; all had received epidural analgesia for labour. Exclusion criteria were any pregnancy with the following factors: gestation of less than 37 weeks, medical disorders (e.g., heart disease, renal disease, diabetes, pre-existing hypertension, and asthma), surgical disorders and obstetric complications (e.g., antepartum haemorrhage, pregnancy-induced hypertension, and preeclampsia). Data collected included maternal age, body mass index, duration of second stage of labour, mode of delivery, birth weight of the baby and Apgar scores. Mode of delivery was our primary outcome measure. Secondary outcome measures were duration of second stage of labour and fetal well-being. Prolonged second stage was defined as more than 3 h of full dilatation, as it is our delivery suite practice to intervene at this stage. Our routine practice for women in labour includes vaginal examinations every 2–3 h (depending on the strength of contractions) until 8 cm dilatation and hourly thereafter until full dilatation. Statistical analysis Data were analysed using SPSS Version 10. Non-parametric tests were used. Categorical data were expressed as proportions, comparisons were made using v2 test and risk was expressed as odds ratio with 95% confidence intervals. Maternal age, body mass index and birth weight of the baby were compared using Mann–Whitney U test. A P value of <0.05 was considered significant. Logistic regression was used to assess independent risk factors for instrumental delivery.
RESULTS The sample number in each group after strict application of inclusion and exclusion criteria was comparable (n ¼ 201 vs. n ¼ 209). Both the groups were similar in
Table 1. Characteristics of the sample groups. Median (range)
Sample characteristics Maternal age (years) Body mass index (kg m2 ) Birth weight (g) Gestational age (weeks)
Group 1 (Continuous infusion) (n ¼ 201)
Group 2 (Intermittent top-ups) (n ¼ 209)
28 (16–45) 27.8 (15–44) 23.8 (16–43) 23.7 (14–42) 3450 (2060–4450) 3440 (2450–4590) 40 (37–42) 40 (37–42)
Mann–Whitney test: there were no significant differences between the groups.
age, body mass index, gestational age, and birth weight (Table 1). Although there appeared to be an increased number of women with assisted vaginal delivery and prolonged second stage of labour in the group that received continuous infusion compared to those who had intermittent top-ups, these differences were not statistically significant (Table 2). There were also no significant differences in the caesarean section rate or Apgar scores (Table 2). Using logistic regression with instrumental delivery as the outcome, the only independent factors affecting outcome were maternal age (OR 1.09, CI 1.05–1.13) and the birth weight of the baby (OR 1.001, CI 1.000– 1.001). Older women with larger babies were at a higher risk of assisted vaginal delivery irrespective of whether they had received continuous or intermittent top-ups of epidural analgesia during labour. DISCUSSION Despite auditing a reasonable number of records, we were unable to demonstrate any significant differences in the outcome of labour between our two groups. The presumed decrease in motor blockade between the two techniques used for labour analgesia did not significantly alter the proportion of women with a prolonged second stage of labour and the number of operative vaginal or caesarean deliveries. Studies that have examined local anaesthetic use prospectively have shown a reduction in the total local
Table 2. Outcome of labour
Labour outcome Mode of delivery Spontaneous vaginal Instrumental Caesarean section Second stage >180 min Apgar score below 7 1 min 5 min
Group 1 (Continuous infusion) (n ¼ 201) 59 83 59 50
(29.4%) (41.3%) (29.4%) (31.6%)
21 (10.5%) 4 (2%)
Group 2 (Intermittent top-ups) (n ¼ 209) 70 78 61 47
(33.5%) (37.3%) (29.2%) (29.2%)
19 (9.1%) 3 (1.4%)
Odds ratio (95% Confidence interval)
0.8 1.2 1.0 1.1
(0.5–1.2) (0.7–2.0) (0.6–1.5) (0.6–1.8)
0.8 (0.4–1.6) 0.7 (0.1–3.2)
Continuous infusion versus midwife top-ups for labour analgesia 11 anaesthetic dose required to maintain labour analgesia, with intermittent top ups as opposed to continuous infusions of the same solution.6–8 Although this method of reducing the local anaesthetic dose has led to decreased motor blockade, benefits regarding obstetric outcome have not been consistent. Some authors have reported a decrease in the instrumental delivery rate,6;9 especially when high dose and low dose top-ups are compared. When low dose epidural solutions are compared using different delivery systems, the difference in motor block has presumably been smaller than with any high dose regimes and there has been no differences in outcome of labour.8;9 We assumed in this study that the mothers experienced a reduction in motor block over these two time periods. This assumption is based on the many prospective studies comparing top-ups and infusions of the same solution and the reports from the midwives looking after the mothers (personal communication) who noticed that many mothers were much more mobile than before the change of practice. We accept that this is not objective evidence and there is a possibility of bias. Although motor block is commonly assessed in terms of the motherÕs ability to move her legs, there has never been a study that examined the effect of these different epidural regimes on perineal analgesia or pelvic floor tone. Neither reduced motor blockade,4 nor ambulation10;11 among those with little motor block, appear per se to improve obstetric outcome. There are obstetric differences, such as degree of extension and position of the fetal head, shape of the maternal pelvis, strength of contractions, age of the mother and size of the baby, which might contribute to the final obstetric outcome. Furthermore, it is possible that women with some of these unfavourable factors are motivated by the midwifery and medical staff to opt for epidural analgesia, with anticipation for its requirement at a later stage. Similar findings were suggested by Yancey et al.12 This may mean that we are dealing with a group of women in whom a delay in second stage of labour and operative delivery rate is going to be higher anyway than the nonepidural group, and by simply reducing motor blockade further in these mothers, it is unlikely that there would be a major impact on operative delivery rates. We noted that increasing maternal age and birth weight were independent risk factors for operative vaginal delivery. Studies have reported that older mothers and those with large babies are at a higher risk of operative vaginal delivery.13–14 Although we recognise that the retrospective nature of this study poses limitations, as it was not possible to
obtain information on the amount of bupivacaine used, the density of motor blockade, quality of analgesia and maternal satisfaction, there seems to be growing evidence that reducing motor block further does not change the outcome of labour. Changing epidurals from high dose to low dose bupivacaine with an opioid seems to reduce obstetric intervention, but the high intervention rate in both our groups of mothers reflects either an aspect of the block that is unchanged (such as perineal analgesia/motor block) or obstetric risk factors that we can not influence.
REFERENCES 1. Burnstein R, Buckland R, Pickett J A. A survey of epidural analgesia for labour in the United Kingdom. Anaesthesia 1999; 54: 634–640. 2. Howell CJ, Epidural versus non-epidural analgesia for pain relief in labour (Cochrane Review). In: The Cochrane Library, 2nd ed. Update Software: Oxford. 3. Echt M, Begneaud W, Montgomery D. Effect of epidural analgesia on the primary caesarean section and forceps delivery rates. J Reprod Med 2000; 45: 557–561. 4. Russell R, Reynolds F. Epidural infusion of low-dose bupivacaine and opioid in labour. Does reducing motor block increase the spontaneous delivery rate? Anaesthesia 1996; 51: 266–273. 5. Collis R E, Baxandall M L, Srikantharajah I D, Edge G, Kadim M Y, Morgan B M. Combined spinal epidural (CSE) analgesia technique, management and outcome of 300 mothers. International Journal Obstetric Anesthesia 1994; 3: 75–81. 6. Smedstad K G, Morison D H. A comparative study of continuous and intermittent epidural analgesia for labour and delivery. Can J Anaesth 1988; 35: 234–241. 7. Collis R E, Plaat F S, Morgan B M. Comparison of midwife top-ups; continuous infusion and patient controlled epidural analgesia for maintaining mobility after a low-dose combined spinal–epidural. Br J Anaesth 1999; 82: 233–236. 8. Purdie J, Reid J, Thorburn J, Asbury A J. Continuous extradural analgesia: comparison of midwife top-ups, continuous infusions and patient controlled administration. Br J Anaesth 1992; 68: 580–584. 9. 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: 19–23. 10. Collis R E, Harding S A, Morgan B M. Effect of maternal ambulation on labour with low-dose combined spinal epidural analgesia. Anaesthesia 1999; 54: 535–539. 11. Bloom S L, McIntire D D, Kelly M A, et al. Lack of effect of walking on labor and delivery. N Engl J Med 1998; 339: 76–79. 12. Yancey M K, Pierce B, Schweitzer D, Daniels D. Observations on labor epidural analgesia and operative delivery rates. Am J Obstet Gynecol 1999; 180: 353–359. 13. Bahar A M. Risk factors and fetal outcome in cases of shoulder dystocia compared with normal deliveries of a similar birth weight. Br J Obstet Gynaecol 1996; 103: 868–872. 14. Ezra Y, McParland P, Farine D. High delivery intervention rates in nulliparous women over age 35. Eur J Obstet Gynecol Reprod Biol 1995; 62: 203–207.