|Year : 2021 | Volume
| Issue : 3 | Page : 221-227
Efficacy of sterile water block with or without antispasmodics for labor analgesia: A triple-arm, randomized controlled trial
Sayeka Mubin, Nazia Tauheed, Muazzam Hasan, Shahla Haleem
Department of Anaesthesiology and Critical Care, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh, Uttar Pradesh, India
|Date of Submission||15-Sep-2020|
|Date of Decision||28-Dec-2020|
|Date of Acceptance||02-Mar-2021|
|Date of Web Publication||29-Dec-2021|
Prof. Shahla Haleem
Department of Anaesthesiology and Critical Care, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Background: Universal provision of safe, effective, and inexpensive analgesia for labor remains a challenge. In India, antispasmodics, especially drotaverine, are widely used as an adjunct to decrease labor pain and duration. Therefore, we aimed to determine the efficacy of sterile water block (SWB), with or without drotaverine. Materials and Methods: This study was a randomized, triple arm, controlled trial on 105 patients in active labor, assigned to receive either intramuscular drotaverine (Group D), Intradermal SWB (Group B), or drotaverine with SWB (Group DB). SWB was given in Michaelis Rhomboid, in active phase of the first stage of labor. Primary outcomes were extent of pain relief, as measured by the numeric rating scale (NRS). Other outcomes included patient's satisfaction, duration of active phase of first stage of labor, APGAR scores, incidence of instrumentation or cesarean section, and any adverse effects. Results: One hundred and five patients were randomized into three groups of 35 patients each. At 30 min postintervention, mean (± standard deviation) NRS score was 7.30 (±1.03), 4.88 (±0.68), and 5.04 (±0.75) in Group D, B, and DB, respectively; (P < 0.001). Two hours' postintervention, NRS was 7.61 ± 0.89, 6.66 ± 0.91, and 6.95 ± 0.85 in Groups D, B, and DB respectively with P < 0.01. Number of patients satisfied in Group D, B, and DB were 0, 24, and 25, respectively. The duration of active phase of 1st stage of labor was 144.80 (±47.46), 198.88 (±92.16), and 142.50 (±50.77) minutes in Group D, B, and DB, respectively (P < 0.01). APGAR score was comparable in three groups. No adverse effect was seen on mother or fetus except burning sensation at the time of giving SWB. The occurrence of cesarean section was 8 in Group B, 8 in Group D, and 6 in Group DB. Conclusion: SWB is a safe modality for labor analgesia, causing a significant reduction in labor pain, both with and without drotaverine. Although not always effective as a sole modality, it may be effective in reducing the requirement of other analgesics when used in conjunction with other modalities for labor analgesia. Drotaverine may not significantly lower the labor pain alone or in conjunction with SWB. Yet, it significantly decreases the duration of active phase of first stage of labor (CTRI/2019/09/021125).
Keywords: Analgesia, drotaverine, labor, pain management, water block
|How to cite this article:|
Mubin S, Tauheed N, Hasan M, Haleem S. Efficacy of sterile water block with or without antispasmodics for labor analgesia: A triple-arm, randomized controlled trial. Indian J Pain 2021;35:221-7
|How to cite this URL:|
Mubin S, Tauheed N, Hasan M, Haleem S. Efficacy of sterile water block with or without antispasmodics for labor analgesia: A triple-arm, randomized controlled trial. Indian J Pain [serial online] 2021 [cited 2022 Jan 28];35:221-7. Available from: https://www.indianjpain.org/text.asp?2021/35/3/221/334098
| Introduction|| |
Labor pain and its relief have always been of immense concern for pregnant women, their families, and their health care providers. It has been described to be one of the most distressing agonies in a woman's lifetime. Around 60%–68% of primiparous women describe it as being “unbearable, intolerable, extremely severe, or excruciating.” Notably, labor pain is a complex, subjective, and individual experience, involving pain in abdomen, pelvis, perineum and/or low back. Organically speaking, it is caused by the distension and stretching of fibers from the lower uterine segment, and tearing of tissues in the vagina and perineum in an effort to expel the fetus.
Pain management during labor is an essential part of good obstetric care. There are many methods for alleviation of pain including pharmacological and nonpharmacological methods, the latter being classified into low-resource, medium-resource and high-resource interventions. The most effective methods currently used are neuraxial analgesia (classified under high resource interventions) and opioids. Inhaled or intravenous or epidural or combined-spinal-epidural anesthesia, all of which require a trained anesthetist, advanced monitoring, and optimal facilities, are included in the pharmacological methods. Their availability is limited in most developing countries, including large parts of India. Apart from this, repeated maternal administration of opioids carries significant risks of fetal exposure and potential for neonatal respiratory depression.
Among the various nonpharmacological techniques, the sterile water block (SWB) is one of the very old methods. Halsted in 1884 mentioned water as a local anesthetic when injected intracutaneously. In the 1900s, sterile water injections were used to relieve pain during minor surgeries. It was first used in obstetrics in the 1970s and was a very popular option in Sweden.
Childbirth can be divided into three stages; the first stage of labor starts from the onset of true labor pain and ends with full dilatation of the cervix (8–10 cm). The second stage from cervical dilatation to delivery of the baby and the third stage is the delivery of the placenta. At the beginning of the 1st stage of labor, the pain is assigned to segments T11 and T12; moderate intensity, diffusely located visceral pain. By the end of this stage, the pain is assigned to segments T10 and L1 and becomes more severe in nature. Stretching of the uterus and cervix during childbirth lead to stimulation of afferent neurons which ends in the dorsal horns of spinal segments of T10-L1. The skin area, supplied by these spinal segments that receive the stimuli, may experience severe pain in the back and/or groin called as referred (transmitted) pain.,
During the descent of presenting part into the vagina, the pain is predominantly somatic and combined with visceral pain from the uterine contractions. The mechanism of pain relief following intra-cutaneous sterile water injection is described as counter-irritation, by which localized pain felt in one part of the body may be relieved by irritating the skin in the same dermatomal distribution. Intradermal water block causes distention and stretching of the tissue, intense stimulation of trigger points resulting in a paralyzing effect on the nerve fiber function, the more distended tissues, the better the analgesia.” based on gate control theory. Furthermore, distension of skin is thought to cause stimulation of nociceptors and mechanoreceptors.
Considerable debate exists whether SWB is truly effective in labor analgesia or not. Drotaverine structurally related to papaverine, a selective inhibitor of phosphodiesterase 4, is an antispasmodic and has a direct action on smooth muscles, enhancing cervical dilatation during childbirth. To note, drotaverine is used freely in obstetric practice to shorten the duration of labor and to avoid complications related to it.,
Thus, the aim of the current study was to determine whether SWB was effective in managing labor analgesia, with or without drotaverine, as assessed by degree of pain relief and patient satisfaction.
| Materials and Methods|| |
The present study was conducted in the maternity ward of a tertiary care academic medical center. After due approval from the Board of Studies of the department as well as the Institutional Ethics Committee (reference number: 1005/FM), the trial was registered with the Clinical Trials Registry India (CTRI/2019/09/021125).
A study was conducted on patients admitted with labor pain in the months of September, October, and November 2019. Patients were randomly allocated using the lottery method to either drotaverine (Group D), water block (Group B), or drotaverine with water block group (Group DB). A total of 105 patients were enrolled and each of the three groups included 35 patients. Prior to enrollment, a written and informed consent for inclusion in the study was taken from each patient.
The primary objective of this study was to assess the degree of pain relief in terms of a numerical rating scale (NRS). Other objectives included the assessment of patient's satisfaction, duration of active phase of first stage of labor, APGAR score, incidence of instrumentation/aid for normal vaginal delivery, frequency of cesarean section, and any other complication during the study.
Patients who were in the active phase of the first stage of labor, with severe pelvic pain, as measured by NRS score of > 6, were included. They were either primi-or multi-gravida. Patients omitted from the study were those with scarred uterus, fetal demise, fetal distress, multiple pregnancies, malpresentation, cephalopelvic disproportion, medical complications such as heart disease, diabetes mellitus, asthma, myasthenia gravis, glaucoma, psychotic illness, or epilepsy and antepartum hemorrhage and also those not giving an informed consent.
Sample size calculation
Based on our pilot study, mean NRS after 30 min of intervention was 7.0 in drotaverine group and 6.53 in water block group and standard deviation was 0.69, for significance level of 0.05 and power of 80%, 34 patients per group were needed. Thirty-five patients were included in each group [Figure 1].
A detailed preanesthetic check-up including history, clinical examination and routine investigations, as guided by age, was carried out in all patients. Obstetric management was as per standard institutional protocols. Labor was monitored by the WHO-endorsed partogram. The baseline institutional protocol for labor analgesia included intravenous injection hyoscine butylbromide 20 mg at the onset of labor and a repeat dose at the beginning of active phase of the first stage of labor. The second dose of hyoscine was withheld in patients being administered drotaverine, i.e. in patients of Groups D and DB.
Patients in Group D were given injection drotaverine hydrochloride 40 mg IM at the onset of active phase of first stage of labor, up to a maximum of 3 doses 2 h interval each. In Group B, patients were given SWB that was repeated 2 hourly, if required and in Group DB, patients were given injection drotaverine with SWB.
This sterile water injection was given intracutaneously on the lower back, corresponding to Michaelis Rhomboid, using a 25-gauge needle, each injection being of 0.1–0.2 ml, at 4 locations. The points A and B were taken at the level of the posterior superior iliac spine (PSIS) on either side and points C and D being 1 cm medial and 1–2 cm inferior to A and B, thus creating 4 small blebs in the lumbosacral region [Figure 2]. While sharp burning pain occurred on injection, it subsided within a minute, hence not interfering with the pain control being evaluated here.
|Figure 2: Placement of injection for Water Block; Point A and B (dimples of the posterior superior iliac spine). Point C and D (1 cm medial and 1–2 cm inferior to A and B). R refers to Michaelis' rhomboid, also known as the quadrilateral of Michaelis|
Click here to view
Patients were asked to rate their pain on the scale of 0–10, i.e. on NRS. The scale ranged from “no pain” to “unbearable pain.”
NRS score was recorded prior to intervention, then at 30 min and 2 h after the intervention in each group. If NRS was >6 at 2 h, the intervention was repeated, up to a maximum of 3 times. Rescue analgesia was given only when the patient demanded for it. Injection tramadol 50 mg intramuscularly was given as the first line rescue analgesia (not repeated before 6 h). Injection diclofenac 75 mg intramuscularly was given as second-line rescue analgesic. NRS was assessed after 30 min of administering rescue analgesia also. Patients were also asked to grade their level of satisfaction (i.e., very dissatisfied, dissatisfied, neutral, satisfied or very satisfied) after 30 min of intervention. The overall satisfaction question was used to determine a two-category satisfaction outcome by combining patients who answered very dissatisfied, dissatisfied or neutral into one group, and patients who answered satisfied or very satisfied into the second group. Thus, as categorical outcomes, either satisfied or not satisfied was used as the measure of overall satisfaction for all statistical analyses.
Data analysis and storage
Analysis of the data was done with the help of SPSS (Statistical Package for Social Sciences ) for windows, version 25.0, Armonk, NY:IBM corp, using Chi-square test, Kruskal–Wallis test, or analysis of variance (ANOVA) were used for comparison. A P < 0.05 was considered statistically significant. For those comparisons where ANOVA provided a critical F-statistic, ad hoc, unpaired t-tests were done to determine groups with a significant difference.
| Results|| |
Demographic parameters such as age and parity were comparable in the three groups [Table 1]. We have excluded the patients who underwent lower segment cesarean section (LSCS) and assisted deliveries during the study.
The baseline pain scores of patients in all the three study groups, before intervention, were found to be comparable. Baseline mean NRS score was 7.68 ± 1.03, 7.73 ± 0.71 and 7.83 ± 0.75 in Group D, B and DB, respectively; (P = 0.674). After 30 min of the intervention, the mean NRS score was 7.30 ± 1.03, 4.88 ± 0.68 and 5.04 ± 0.75 in Groups D, B and DB, respectively [Table 2]. The pain intensity was decreased significantly in the water block group as compared to only drotaverine group, with F value 121.442 and P = 0.0001. At 2 h after intervention, the mean NRS score was 7.61 ± 0.89, 6.66 ± 0.91 and 6.95 ± 0.85 in Groups D, B, and DB, respectively, with P = 0.0008 [Table 2].
|Table 2: Comparison of Numeric Rating Scale score at baseline, at different follow-up intervals, number of repeat interventions required and number of rescue analgesia demanded|
Click here to view
In Group D, the number of patients in whom intervention was repeated for one time were 16 and two times were 4. In Group B, the number of patients in whom intervention was repeated for one time was 9 and two times were 4. In Group DB, number of patients in whom intervention was repeated for one time was 13 and two times were 2 [Table 2].
First line of rescue analgesia, on demand, was given to 26 patients in Group D, 9 patients in Group B and 10 patients in Group DB [Table 2]. Second line of rescue analgesia, on demand, was given to 10 patients in Group D, 2 patients in Group B, and 3 patients in Group DB [Table 2]. Mean NRS score after first line of rescue analgesia was 3.34 ± 0.79, 3.11 ± 0.60 and 3.3 ± 0.82 in Group D, B, and DB (P > 0.05). Mean NRS score after second line of rescue analgesia was 2.7 ± 0.48, 2.5 ± 0.70 and 2.6 ± 0.84 in Group D, B, and DB, respectively (P > 0.05) [Table 2].
Comparison of frequency and mean distribution delivery outcome was done by patient's satisfaction score, duration of 1st stage of labor, Apgar score, number of assisted vaginal delivery, and incidence of cesarean section among the three groups [Table 3].
| Discussion|| |
The current study was undertaken to evaluate the efficacy of three modalities of the management of labor pain, a major cause of suffering and concern, and one of the main goals of maternity care. The modalities included the SWB, drotaverine injection and the water block along with drotaverine injection.
The participants in the water block intervention group had a statistically significant pain reduction (P < 0.05). There was a significant reduction in the mean NRS score from the baseline observed at 30 min after injections and was sustained for more than 120 min after intervention. This relief was; however, varying in intensity. Similarly, women treated with both drotaverine plus water block (DB) showed a considerable reduction in their mean NRS score, after 30 min and 120 min, comparable with that of Group B [Figure 3]. As the patients were in the process of labor, we cannot anticipate 100% pain relief. Although through these interventions and at times resorting to rescue analgesia, we could reduce the patient's pain to a certain minimum level. Patients who were administered intramuscular drotaverine injections alone (Group D) documented minimal relief in their pain, were also not satisfied with the pain relief method and needed rescue analgesic.
The finding of effective pain relief and patient's satisfaction on sterile water injection as a method of pain relief during labor is in agreement with previous studies.,,,,, However, a Cochrane review by Derry et al. in 2012, which is considered the highest in the evidence pyramid, evaluated all prior randomized controlled trials (RCTs) of SWB in labor and found an insufficient evidence for this claim. Unfortunately, no further review in the past 8 years has been carried for this. Recently, an RCT by Fouly et al. published in 2018, found a significant pain reduction by SWB in labor.
In our study (n = 27), 9 patients required one repeat block and 4 patients required two repeat blocks after 2 h of injection in SWB group. However, Lee et al. have also reported a sustained pain relief for >2 h following sterile water injection.
In the patients given injection drotaverine, there was some reduction in mean NRS score 30 min after the intervention. This may be due to a placebo effect. It has been found that placebo treatment could be antagonized by naloxone supporting the theory that placebo treatment is partly mediated by endogenous opioids.
The counterirritation mechanism also causes the secretion of endorphins similar to that seen with acupuncture. However, the mechanism of this hyperstimulation analgesia is most often explained by the Melzack's gate theory of pain, here the somatic component essentially overwhelming the visceral component.
In the current study, patients in each of the three groups demanded for rescue analgesia. However, it was observed that the number of patients who demanded for rescue analgesia was significantly lower in the SWB groups (Group B and DB) than the individual drotaverine group (Group D) [Table 2]; thus, reducing the requirement of analgesics during labor.
The use of a combination of the two management modalities, i.e. drotaverine and water block, for labor analgesia has not been reported yet.
Regarding the delivery outcome in context to the patient's satisfaction as assessed by patient satisfaction score, most of the patients were satisfied with SWB intervention in either group B or group DB with the results in accordance with other studies.,,, Other studies reported the same but also added that the patients though had a decrease in pain intensity, they still requested for other pain medications, meaning not very satisfactory pain relief., The possible explanation for this finding is that water block reduces only low back pain and not the abdominal pain experienced during labor; and the estimated incidence of low back pain in labor ranges between 15% and 74% of all laboring women.
No significant difference was observed in the mean APGAR score of babies in the three groups, similar to the findings of prior studies.,,,,,,
The current study showed an additional advantage of drotaverine, i.e. it accelerated labor or shortened 1st stage of labor (144.80 ± 47.46 min) in comparison to water block group (198.88 ± 92.16 min). This difference was found to be statistically significant. Drotaverine is used liberally in obstetric practice. An effective reduction in pain and duration of labor was reported by other investigators also due to its antispasmodic action at cervico-uterine plexus helping in cervical dilatation.,,
The duration of 1st stage of labor was 144.80 ± 47.46 min, 198.88 ± 92.16 min, and 142.50 ± 50.67 min in Group D, B, and DB, respectively (F = 6.198, P = 0.01). The duration of labor was reduced maximally in combination group (DB), as compared to group drotaverine alone. This may be due to the shared advantage of drotaverine and water block, thus leading to significant patient satisfaction in this group. Thus, a major cause of increased maternal and neonatal mortality and morbidity may be averted; 4.1% of maternal deaths in Africa was found to be due to prolonged obstructed labor.,
The incidence of instrumentation, LSCS was comparable in the three intervention groups as reported by other studies as well., No adverse effect was seen in either the mother or fetus in any group, except burning pain at the time of water block injections which lasted for a few seconds; this was also similar to other studies.,,
Although there was a decrease in the pain intensity in patients with all the three interventions, it was observed that none of the study groups showed a decline of NRS to < 3; hence, none of these interventions can serve as the sole modality for labor analgesia. However, when used in conjunction with other modalities, the synergistic analgesic effect may provide the advantage of minimizing the dosage of other medications, especially the opioid, a major culprit for neonatal respiratory depression.
A major limitation of this study was the small sample size, a larger one could have led to a better analysis of the interventions. Placebo controls could have given a more clear and vivid picture, as well.
SWB is an inexpensive, safe mode of modality of labor analgesia that can be administered even by a nonanesthetist. Once its training is imparted to obstetricians and medical graduates, a high-quality labor analgesia may be ensured at all levels of health care including primary and community health centers.
| Conclusion|| |
SWB is a simple, safe, and effective treatment method for pain relief during first stage of labor and can be used without major side effects. Women who received sterile water injections experience recordable reduction in labor pain, compared to women given drotaverine alone. The re-injections of sterile water were also able to establish the analgesic effect. Although not always effective as a sole modality, it may be effective in reducing the requirement of other analgesics. It can be learnt easily and can be performed without gaining much experience. Drotaverine injection alone is not very helpful for analgesia; it is useful as an adjunct to reduce the duration of active phase of the first stage of labor.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Melzack R. The myth of painless childbirth (the John J. Bonica lecture). Pain 1984;19:321-37.
McDonald JS, Noback CR. Deep and visceral pain. In: Melzack R, Patrick D, editors. Wall Obstetric Pain from Handbook of Pain Management, A Clinical Companion to Wall and Melzack's Textbook of Pain. Ch. 11. London: Elsevier ,Churchill Livingstone; 2003.
Caughey AB. Nonpharmacologic approaches to management of labour pain. In: Post TW, editor. UpToDate. Waltham, MA: UpToDate; 2004; uptodate.com/contents/nonpharmacological-approaches to management-of-labour-pain. [Last accessed on 2020 June 20].
Schrock SD, Harraway-Smith C. Labor analgesia. Am Fam Physician 2012;85:447-54.
Halsted W. Water as a local anaesthetic. Med J 1885;3:23-7.
McDonald J. Obstetric pain. In: McMahon S, Koltzenburg M, editors. Wall and Melzack×s Textbook of Pain, Section 5, Clinical States: Viscera. 5th
ed., Ch. 52. London: Elsevier Churchill Livingstone; 2006. p. 793-816.
Moore S. Understanding Pain and its Relief in Labour. 1th
ed. New York: Churchill Livingstone; 1997.
Haleem S. Anaesthesia and analgesia for labour and vaginal delivery for safe obstetric practice. Acad Anesthesiol Int 2017;2:12-20.
Launois R. The treatment of sciatica and neuralgia by subcutaneous injections of salt water. Med Press 1906;9:497.
Anon A. Anaesthesia with sterile water. Med Press 1904;24:217-8.
Drotaverine Drug Information | Drugs Update India. Available from: http://www.drugsupdate.com/generic/view/826/Drotaverine
. [Last accessedon 2019 Dec 09].13. Singh KC, Jain P, Goel N, Saxena A. Drotaverine hydrochloride for augmentation of labor. Int J Gynaecol Obstet 2004;84:17-22.
Sharma JB, Pundir P, Kumar A, Murthy NS. Drotaverine hydrochloride vs. valethamate bromide in acceleration of labor. Int J Gynaecol Obstet 2001;74:255-60.
Derry S, Straube S, Moore RA, Hancock H, Collins SL. Intracutaneous or subcutaneous sterile water injection comp ared with b linded controls for pain management in labour. Cochrane Database Syst Rev 2012; Jan 18, issue 1:CD009107.John wiley and sons, Ltd. Available from: http://doi.wiley.com/10.1002/14651858. CD009107.pub2
. [Last accessed on 2019 Nov 08].
Fouly H, Herdan R, Habib D, Yeh C. Effectiveness of injecting lower dose subcutaneous sterile water versus saline to relief labour back pain: Randomized controlled trial. Eur J Midwifery 2018;2:3.
Saxena KN, Nischal H, Batra S. Intracutaneous injections of sterile water over the secrum for labour analgesia. Indian J Anaesth 2009;53:169-73.
Geltore TE, Taye A, Kelbore AG. Utilization of obstetric analgesia in labor pain management and associated factors among obstetric caregivers in public health facilities of Kembata Tembaro Zone, Southern Ethiopia. J Pain Res 2018;11:3089-97.
] [Full text]
Wiruchpongsanon P. Relief of low back labour pain by using intracutaneous injections of sterile water: A randomized clinical trial. J Med Assoc Thail Chotmaihet Thangphaet 2006;89:571-6.
Ader L, Hansson B, Wallin G. Parturition pain treated by intracutaneous injections of sterile water. Pain 1990;41:133-8.
Bahasadri S, Ahmadi-Abhari S, Dehghani-Nik M, Habibi GR. Subcutaneous sterile water injection for labour pain: A randomised controlled trial. Aust N Z J Obstet Gynaecol 2006;46:102-6.
Mårtensson L, Wallin G. Sterile water injections as treatment for low-back pain during labour: A review. Aust N Z J Obstet Gynaecol 2008;48:369-74.
Lee N, Webster J, Beckmann M, Gibbons K, Smith T, Stapleton H, et al.
Comparison of a single vs a four intradermal sterile water injection for relief of lower back pain for women in labour: A randomized controlled trial. Midwifery 2013;29:585-91.
Colloca L. The placebo effect in pain therapies. Annu Rev Pharmacol Toxicol 2019;59:191-211.
Melzack R, Schaffelberg D. Low-back pain during labor. Am J Obstet Gynecol 1987;156:901-5.
Simkin P, O'Hara M. Nonpharmacologic relief of pain during labour: Systematic reviews of five methods. Am J Obstet Gynecol 2002;186:S131-59.
Trolle B, Møller M, Kronborg H, Thomsen S. The effect of sterile water blocks on low back labor pain. Am J Obstet Gynecol 1991;164:1277-81.
LaBrecque M, Nouwen A, Bergeron M, Rancourt J. A randomized controlled trial of nonpharmacologic approaches for pain relief for low back pain during labour. J Fam Pract 1999;48:259-63.
Reynolds JL. Practice tips. Intracutaneous sterile water injections for low back pain during labour. Can Fam Physician 1998;44:2391-2.
Simkin P, Bolding A. Update on nonpharmacologic approaches to relieve labour pain and prevent suffering. J Midwifery Womens Health 2004;49:489-504.
Gagnon A, Waghorn K, Covell C. A randomized trial of one-to-one nurse support of women in labour. Birth 1997;24:71-80.
Langer A, Campero L, Garcia C, Reynoso S. Effects of psychosocial support during labour and childbirth on breast-feeding, medical interventions, and mothers' well-being in Mexican public hospital: A randomized clinical trial. Br J Obstet Gynaecol 1998;105;1056-63.
Hodnett ED, Lowe NK, Hannah ME, Willan AR, Stevens B, Weston JA, et al.
Effectiveness of nurses as providers of birth labor support in North American hospitals: A randomized controlled trial. JAMA 2002;288:1373-81.
Khan KS, Wojdyla D, Say L, Gülmezoglu AM, Van Look PF. WHO analysis of causes of maternal death: A systematic review. Lancet 2006;367:1066-74.
Ohwer AC, Khondowe O, Young T. Antispasmodics for labour. Cochrane Database Syst Rev 2012;15:CD009243.
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]