The Journal of Maternal-Fetal & Neonatal Medicine
ISSN: 1476-7058 (Print) 1476-4954 (Online) Journal homepage: http://www.tandfonline.com/loi/ijmf20
Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes Liran Hiersch, Liat Salzer, Amir Aviram, Avi Ben-Haroush, Eran Ashwal & Yariv Yogev To cite this article: Liran Hiersch, Liat Salzer, Amir Aviram, Avi Ben-Haroush, Eran Ashwal & Yariv Yogev (2015) Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes, The Journal of Maternal-Fetal & Neonatal Medicine, 28:14, 1633-1636, DOI: 10.3109/14767058.2014.964677 To link to this article: http://dx.doi.org/10.3109/14767058.2014.964677
Accepted online: 12 Sep 2014.Published online: 29 Sep 2014.
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Date: 10 October 2015, At: 00:37
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, 2015; 28(14): 1633–1636 ! 2014 Informa UK Ltd. DOI: 10.3109/14767058.2014.964677
ORIGINAL ARTICLE
Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes Liran Hiersch1,2, Liat Salzer1,2, Amir Aviram1,2, Avi Ben-Haroush1,2, Eran Ashwal1,2, and Yariv Yogev1,2 Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, Petach Tikva, Israel and 2Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
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Abstract
Keywords
Objective: Limited data exist regarding uterine contraction intensity prior to membrane rupture. Using a novel technique of electrical uterine myography (EUM) we aimed to determine which factors affect myometrial activity during active phase of labor. Methods: EUM was prospectively measured in 37 women with singleton pregnancy at term during the active phase of labor until membranes’ rupture. EUM was measured using noninvasive nine channels recorder with an EMG amplifier and three-dimensional position sensor. Uterine electrical activity was quantified with the EUM-index, defined as the mean electrical activity of the uterine muscle over a period of 10 min and measured in units of micro-Joule (microwatt per second [mW/s]). Results: The mean EUM-index at the first 10 min of the measurement was 3.3 ± 0.6 mW/s. In a stepwise linear regression model accounting potential confounders EUM was significantly affected by cervical dilatation (p ¼ 0.005), maternal age (p ¼ 0.04) and previous cesarean delivery status (p ¼ 0.02). In a repeated measurement assessment of non-parametric Fridman’s test for all subjects who had at least 10 continuouss EUM measurements, there was a significant increase in electrical uterine activity as labor progressed (p ¼ 0.01). Conclusion: Electrical uterine activity during the active phase of labor prior to rupture of membranes is affected by maternal age, previous cesarean delivery status and cervical dilatation. Moreover, electrical uterine activity is enhanced throughout labor.
Active phase, delivery, uterine activity
Introduction Uterine activity is characterized by the frequency, intensity, and duration of uterine muscle contractions. Adequate labor is defined classically as three to five contractions per 10 min with advance in cervical effacement and dilation and fetal descent [1]. Conventional methods for uterine contractions monitoring are limited as external tocodynamometry is lacking the capability of quantitative uterine contractions intensity assessment and intrauterine pressure catheter application is only feasible following membranes rupture [2,3]. Measurement of uterine activity using intrauterine pressure transducers is quantified using Montevideo units (calculated by multiplying the average peak strength of contractions in mm Hg by the number of contractions in 10 min). Using this method, observational studies have found that adequate labor
Address for correspondence: Yariv Yogev, Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, Petah Tiqwa 49100, Israel. Tel: +972-3-9377680. E-mail: [email protected]
History Received 25 August 2014 Accepted 9 September 2014 Published online 29 September 2014
is usually observed with 200–250 Montevideo units [4,5]. There is no evidence that one method is significantly better than another [6] and still, despite technologic improvements, the definition of ‘‘adequate’’ uterine activity during labor remains vague. Moreover, information regarding quantitative measurement of contractions intensity through the different stages of labor is lacking. Recently, the use of electrical uterine myography Monitoring (EUM) for the assessment of electrical uterine activity was introduced. EUM is a non-invasive method allowing the evaluation of duration, frequency and most importantly the intensity of uterine contractions [7–9]. Moreover, its accuracy in assessing contractions intensity is comparable to that of intrauterine pressure catheter [10]. Quantitative measurement of contractions intensity during active phase may shed light on the uterine factor that contributes to labor dystocia, and can possibly explain the mechanism behind known risk factors for protraction and arrest disorders such as maternal obesity [11,12], neuroaxial anesthesia [13], etc. Thus, we aimed to explore which factors could affect uterine myometrial activity during active phase of labor prior to membrane rupture using a novel technique of EUM.
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Methods
Statistical analysis
Study population
Data analysis was performed with the SPSS v19.0 package (Chicago, IL). A non-parametric Friedman’s test was carried out in order to assess if there were differences in perceived EUM measurements based on cervical dilatation throughout labor. A stepwise linear regression model was used to adjust the effect on labor EUM measurements. Variables that were hypothesized to potentially affect the likelihood of EUM measurements based on clinical grounds were entered to the stepwise linear logistic regression model. Differences were considered significant when p-value was less than 0.05.
We conducted a prospective observational study of women undergoing labor and delivery at a single tertiary university affiliated medical center. Eligibility was limited to singleton term (37 + 0 weeks of gestation) pregnancies with intact membranes, within the active phase of labor defined as cervical dilatation between 4 and 9 cm. The study was approved by the local institutional review board, and all women provided written informed consent prior to participating in the study. Study design
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J Matern Fetal Neonatal Med, 2015; 28(14): 1633–1636
Women in active phase of labor with intact membranes were connected to EUM. In addition, all women were monitored by external tocodynamometer and electronic fetal heart rate monitoring, which are routinely used in all deliveries. All decisions regarding labor management including the frequency of cervical dilatation examination, need for oxytocin for augmentation or dosage changing, or artificial rupture of membranes (AROM) timing were made solely by the attending physician and were based on the routinely used external tocodynamometer and other clinical signs and symptoms. The attending physician and research team were blinded to the EUM results. Women who were augmented with oxytocin but had dosage changes during EUM monitoring period were subsequently excluded from final analysis. Data collection The following data were collected for each participant: demographic and obstetric characteristics, administration of oxytocin, cervical dynamics during EUM monitoring period and EUM recordings. The EUM device A novel EMG device, EUM-100 (OB-Tools Ltd, MigdalHaemek, Israel), was used to measure the electrical uterine activity. The system is comprised of a multichannel surface electromyogram, a three-dimensional position sensor and a personal computer providing data analysis and a graphical user interface. The EUM signals are acquired and amplified using a proprietary isolated amplifier box based on modified Teledyne A0401 modules (Teledyne Inc, Thousand Oaks, CA). The surface EUM activity is acquired by nine electrodes evenly placed on the patient’s abdomen and a tenth common ground electrode on the patient’s left thigh. The measurement of EUM signals together with their physical location provides an accurate estimation of the uterine activity in the three-dimensional space. The electrical signal from the myometrium is recorded and processed using a uterine contractility algorithm. Uterine muscle activity is quantified using the EUM scoring index which is defined as the mean electrical activity of the uterine muscle over a period of 10 min and is measured in units of micro-Joule (micro-Watt-Second, mWS) with an automatic data analyzer blinded to clinical outcome.
Results Overall, 37 women with singleton pregnancies at term were enrolled. The demographic and obstetrical characteristics are presented in Table 1. Mean maternal age was 30.8 ± 4.5 years and 24% were nulliparous. Eleven women were evaluated for more than 100 min. Mean EUM-index at the first 10 min of the exam (EUM1) for all women was 3.3 ± 0.6mWS, and was referred as baseline. Sixty-five cervical dilatation examinations during active phase of labor prior to membranes’ rupture were analyzed. Thirty-two (68%) women had more than one cervical dilatation measurement. In a stepwise linear regression model accounting for maternal age, gravity, parity, gestational age, BMI, previous cesarean delivery status, cervical dilatation and the use of oxytocin in labor, EUM was significantly affected by cervical dilatation (p ¼ 0.005, Figure 1), maternal age (p ¼ 0.04) and previous cesarean delivery status (p ¼ 0.02). In a repeated measurement, a non-parametric Fridman’s test for all subjects who have had at least 10 continues EUM measurements was performed (N ¼ 11). There was a significant increase in electrical uterine activity as labor progressed (p ¼ 0.01, Figure 2).
Discussion In the current study, we prospectively assessed factors affecting uterine electrical activity during active phase of Table 1. Demographic and obstetrical characteristics of the study group.
Variable
Study group (n ¼ 37)
Maternal age (years) Gestational age (weeks) Gravidity Parity Nulliparity Previous CS BMI at admission (kg/m2) Oxytocin use during labory Number of cervical dilatation measurements per patient 1 2 3 Duration of EUM monitoring (min)* Duration 4100 min*
30.8 ± 4.5 39.2 ± 1.0 2.7 ± 1.3 1.4 ± 1.0 9 (24.3%) 3 (8.1%) 26.8 ± 3.9 16 (43.2%) 1.8 ± 0.6 12 (32.4%) 22 (59.5%) 3 (8.1%) 98.1 ± 60.0 11 (44%)
Data are presented as mean ± SD or n (%). *Among 25 women with at least two cervical dilatation measurements. yNo change in oxytocin dosage during EUM monitoring period. BMI, body mass index; CS, cesarean section; EUM, electrical uterine myography.
DOI: 10.3109/14767058.2014.964677
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labor prior to membranes’ rupture using novel EUM technology. Our main findings were: (1) Overall, EUMindex (uterine activity) is enhanced with increase in cervical dilation during the active phase as labor progresses. (2) Previous cesarean delivery status and lower maternal age is associated with higher uterine activity. BMI was not significantly associated with EUM-index. The traditional methods for assessment of uterine contraction intensity are limited. Intrauterine pressure catheter necessitates ruptured membranes prior to application. Moreover, the method is invasive and thus has potential for complications. The technology of EUM used in the current study and its non-invasive nature, enabled performing quantification of uterine contractions intensity in the active phase while membranes are intact. Previous study from our group [14] has demonstrated that myometrial electrical activity recorded by the EUM is significantly enhanced following AROM. Thus, to avoid confounders, we measured uterine
Figure 1. The association between EUM-index and cervical dilatation during the active phase of labor. Data represent EUM-index results at the time of 65 cervical dilatation examinations during active phase labor prior to membranes’ rupture of 32 women. Figure 2. The change in mean EUM measurement during 10 consecutive measurements (a period of 100 min). Borders represent 95% confidence interval.
Uterine electrical activity in the active phase
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activity in the active phase only prior to rupture of membranes. Recent studies focused on quantification of uterine activity during labor [1,15–17]. Still, though outdated evidence exist regarding an increase in uterine activity during labor [18], information on the different intensities of uterine activity through the progress of active phase itself is lacking. Our data may suggest that enhanced electrical myometrial activity through the active phase, may, in part, be responsible for adequate progress in labor. In clinical practice, this may shed light on the mechanisms for pathological progress of labor and be a future therapeutic target. Other than cervical dilation, maternal age was also inversely correlated with EUM-index. It was suggested that older age is associated with a significant decrease in contractility for spontaneous contractions, but only in the non-pregnant state [19]. In the pregnant myometrium, a wide range of contractile ability was found between women and little evidence for decreased spontaneous activity appeared between the ages of 25 and 40. The lack of difference in the pregnant state over this period was attributed to the response to gestational hormones. On the other hand, other studies suggested that advanced maternal age is associated with increase in operative vaginal deliveries, cesarean section, and an increased need for oxytocin-augmentation [20,21]. These findings were shown not to be explained by co-morbidities such as obesity or gestational diabetes. One hypothesis proposed for these findings is that with increasing age, the myometrium is less effective or less responsive to uterotonic agents such as oxytocin or prostaglandins thereby indicating a direct effect of aging on myometrial function [20]. Uterine electrical activity recorded with EUM in our study is in concordance with this hypothesis. Moreover, our results might suggest that uterine activity in women with previous cesarean section is even enhanced. Previous study [22] measuring in vitro myometrial contractility, found that myometrium from women whose previous cesarean section was for fetal distress contracted with more force than that from women whose previous cesarean section was necessary because of other indications. However, our sample size is too small to separate the various indications.
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Previous studies have also found poor spontaneous and oxytocin-stimulated uterine contractility in vitro in postdate pregnancies [23] and obese women [24]. Our study did not confirm these observations. It is possible that the mechanical contractile ability of the myometrium tested in these studies does not necessarily equal electrical activity. Moreover, these studies were made in vitro and there is a possibility that other factors play a role in the in vivo environment that influence the contractility and mask its effect, possibly hormonal effects. The prospective nature of our design and the blinding of both treating physician and research team to EUM measurements during labor as well as blinding of the data analyzer to clinical results strengthen our findings, Still, our study has several limitations. The study was done on a small number of patients. Larger studies are needed to confirm our findings. Since this was an observational study rather than an interventional one, we lacked a control arm. Moreover, as labor was managed by the treating physician, some of the participants had been administered oxytocin prior to recruitment. However, oxytocin dosage was not altered during the reported hour of assessment, which minimizes its bias effect. In conclusion, we demonstrated that electrical uterine activity during the active phase of labor prior to rupture of membranes is affected by cervical dilatation, maternal age, and previous cesarean delivery status. Moreover, electrical uterine activity is enhanced throughout labor. Further research is warranted in order to describe electrical uterine activity in pathological labors for better future clinical purposes.
Declaration of interest The authors report no conflict of interest.
References 1. Krapohl AJ, Myers GG, Caldeyro-Barcia R. Uterine contractions in spontaneous labor. A quantitative study. Am J Obstet Gynecol 1970;1:378–87. 2. Maul H, Maner WL, Olson G, et al. Noninvasive transabdominal uterineelectromyography correlates with the strength of intrauterine pressure and is predictive of labor and delivery. J Matern Fetal Neonatal Med 2004;15:297–301. 3. Newman RB. Uterine contraction assessment. Obstet Gynecol Clin North Am 2005;32:341–67. 4. Caldeyro-Barcia R, Sica-Blanco Y, Poseiro JJ, et al. A quantitative study of the action of synthetic oxytocin on the pregnant human uterus. J Pharmacol Exp Ther 1957;121:18–31.
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5. Hauth JC, Hankins GD, Gilstrap III LC, et al. Uterine contraction pressures with oxytocin induction/augmentation. Obstet Gynecol 1986;68:305–9. 6. Chua S, Kurup A, Arulkumaran S, Ratnam SS. Augmentation of labor: does internal tocography result in better obstetric outcome than external tocography? Obstet Gynecol 1990;76:164–7. 7. Most O, Langer O, Kerner R, et al. Can myometrial electrical activity identify patients in preterm labor? Am J Obstet Gynecol 2008;199:378.e1–6. 8. Hadar E, Melamed N, Aviram A, et al. Effect of an oxytocin receptor antagonist (atosiban) on uterine electrical activity. Am J Obstet Gynecol 2013;209:384.e1–7. 9. Aviram A, Melamed N, Hadar E, et al. Effect of prostaglandin E2 on myometrial electrical activity in women undergoing induction of labor. Am J Perinatol 2014;31:413–8. 10. Haran G, Elbaz M, Fejgin MD, Biron-Shental T. A comparison of surface acquired uterine electromyography and intrauterine pressure catheter to assess uterine activity. Am J Obstet Gynecol 2012; 206:412.e1–5. 11. Kominiarek MA, Zhang J, Vanveldhuisen P, et al. Contemporary labor patterns: the impact of maternal body mass index. Am J Obstet Gynecol 2011;205:244.e1. 12. Robinson BK, Mapp DC, Bloom SL, et al. Increasing maternal body mass index and characteristics of the second stage of labor. Obstet Gynecol 2011;118:1309–13. 13. Anim-Somuah M, Smyth RM, Jones L. Epidural versus nonepidural or no analgesia in labour. Cochrane Database Syst Rev 2011;7:CD000331. 14. Hiersch L, Rosen H, Salzer L, et al. Does artificial rupturing of membranes inthe active phase of labor enhance myometrial electrical activity? J Matern Fetal Neonatal Med 2014. [Epub ahead of print]. doi:10.3109/14767058.2014.927431. 15. Althaus JE, Petersen S, Driggers R, et al. Cephalopelvic disproportion is associated with an altered uterine contraction shape in the active phase of labor. Am J Obstet Gynecol 2006;195:739–42. 16. Bakker PC, Van Rijswijk S, van Geijn HP. Uterine activity monitoring during labor. J Perinat Med 2007;35:468–77. 17. Galinimoghaddam T, Moslemizadeh N, Seifollahpour Z, et al. Uterine contractions’ pattern in active phase of labor as a predictor of failure to progress. Glob J Health Sci 2014;6:200–5. 18. Arulkumaran S, Gibb DMF, Ingemarsson I, et al. Uterine activity during spontaneous labor after previous lower-segment cesarean section. Br J Obstet Gynaecol 1989;96:933–8. 19. Arrowsmith S, Robinson H, Noble K, Wray S. What do we know about what happens to myometrial function as women age? J Muscle Res Cell Motil 2012;33:209–17. 20. Greenberg MB, Cheng YW, Sullivan M, et al. Does length of labor vary by maternal age? Am J Obstet Gynecol 2007;197:428.e1–7. 21. Main DM, Main EK, Moore DH. The relationship between maternal age and uterine dysfunction: a continuous effect throughout reproductive life. Am J Obstet Gynecol 2000;182:1312–20. 22. Quenby S, Matthew A, Zhang J, et al. In vitro myometrial contractility reflects indication for caesarean section. BJOG 2011; 118:1499–506. 23. Arrowsmith S, Quenby S, Weeks A, et al. Poor spontaneous and oxytocin-stimulated contractility in human myometrium from postdates pregnancies. PLoS One 2012;7:e36787. 24. Zhang J, Bricker L, Wray S, Quenby S. Poor uterine contractility in obese women. BJOG 2007;114:343–8.
ISSN: 1476-7058 (Print) 1476-4954 (Online) Journal homepage: http://www.tandfonline.com/loi/ijmf20
Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes Liran Hiersch, Liat Salzer, Amir Aviram, Avi Ben-Haroush, Eran Ashwal & Yariv Yogev To cite this article: Liran Hiersch, Liat Salzer, Amir Aviram, Avi Ben-Haroush, Eran Ashwal & Yariv Yogev (2015) Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes, The Journal of Maternal-Fetal & Neonatal Medicine, 28:14, 1633-1636, DOI: 10.3109/14767058.2014.964677 To link to this article: http://dx.doi.org/10.3109/14767058.2014.964677
Accepted online: 12 Sep 2014.Published online: 29 Sep 2014.
Submit your article to this journal
Article views: 35
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmf20 Download by: [Universite Laval]
Date: 10 October 2015, At: 00:37
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, 2015; 28(14): 1633–1636 ! 2014 Informa UK Ltd. DOI: 10.3109/14767058.2014.964677
ORIGINAL ARTICLE
Factors affecting uterine electrical activity during the active phase of labor prior to rupture of membranes Liran Hiersch1,2, Liat Salzer1,2, Amir Aviram1,2, Avi Ben-Haroush1,2, Eran Ashwal1,2, and Yariv Yogev1,2 Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, Petach Tikva, Israel and 2Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
Downloaded by [Universite Laval] at 00:37 10 October 2015
1
Abstract
Keywords
Objective: Limited data exist regarding uterine contraction intensity prior to membrane rupture. Using a novel technique of electrical uterine myography (EUM) we aimed to determine which factors affect myometrial activity during active phase of labor. Methods: EUM was prospectively measured in 37 women with singleton pregnancy at term during the active phase of labor until membranes’ rupture. EUM was measured using noninvasive nine channels recorder with an EMG amplifier and three-dimensional position sensor. Uterine electrical activity was quantified with the EUM-index, defined as the mean electrical activity of the uterine muscle over a period of 10 min and measured in units of micro-Joule (microwatt per second [mW/s]). Results: The mean EUM-index at the first 10 min of the measurement was 3.3 ± 0.6 mW/s. In a stepwise linear regression model accounting potential confounders EUM was significantly affected by cervical dilatation (p ¼ 0.005), maternal age (p ¼ 0.04) and previous cesarean delivery status (p ¼ 0.02). In a repeated measurement assessment of non-parametric Fridman’s test for all subjects who had at least 10 continuouss EUM measurements, there was a significant increase in electrical uterine activity as labor progressed (p ¼ 0.01). Conclusion: Electrical uterine activity during the active phase of labor prior to rupture of membranes is affected by maternal age, previous cesarean delivery status and cervical dilatation. Moreover, electrical uterine activity is enhanced throughout labor.
Active phase, delivery, uterine activity
Introduction Uterine activity is characterized by the frequency, intensity, and duration of uterine muscle contractions. Adequate labor is defined classically as three to five contractions per 10 min with advance in cervical effacement and dilation and fetal descent [1]. Conventional methods for uterine contractions monitoring are limited as external tocodynamometry is lacking the capability of quantitative uterine contractions intensity assessment and intrauterine pressure catheter application is only feasible following membranes rupture [2,3]. Measurement of uterine activity using intrauterine pressure transducers is quantified using Montevideo units (calculated by multiplying the average peak strength of contractions in mm Hg by the number of contractions in 10 min). Using this method, observational studies have found that adequate labor
Address for correspondence: Yariv Yogev, Department of Obstetrics and Gynecology, Helen Schneider Hospital for Women, Rabin Medical Center, Petah Tiqwa 49100, Israel. Tel: +972-3-9377680. E-mail: [email protected]
History Received 25 August 2014 Accepted 9 September 2014 Published online 29 September 2014
is usually observed with 200–250 Montevideo units [4,5]. There is no evidence that one method is significantly better than another [6] and still, despite technologic improvements, the definition of ‘‘adequate’’ uterine activity during labor remains vague. Moreover, information regarding quantitative measurement of contractions intensity through the different stages of labor is lacking. Recently, the use of electrical uterine myography Monitoring (EUM) for the assessment of electrical uterine activity was introduced. EUM is a non-invasive method allowing the evaluation of duration, frequency and most importantly the intensity of uterine contractions [7–9]. Moreover, its accuracy in assessing contractions intensity is comparable to that of intrauterine pressure catheter [10]. Quantitative measurement of contractions intensity during active phase may shed light on the uterine factor that contributes to labor dystocia, and can possibly explain the mechanism behind known risk factors for protraction and arrest disorders such as maternal obesity [11,12], neuroaxial anesthesia [13], etc. Thus, we aimed to explore which factors could affect uterine myometrial activity during active phase of labor prior to membrane rupture using a novel technique of EUM.
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Methods
Statistical analysis
Study population
Data analysis was performed with the SPSS v19.0 package (Chicago, IL). A non-parametric Friedman’s test was carried out in order to assess if there were differences in perceived EUM measurements based on cervical dilatation throughout labor. A stepwise linear regression model was used to adjust the effect on labor EUM measurements. Variables that were hypothesized to potentially affect the likelihood of EUM measurements based on clinical grounds were entered to the stepwise linear logistic regression model. Differences were considered significant when p-value was less than 0.05.
We conducted a prospective observational study of women undergoing labor and delivery at a single tertiary university affiliated medical center. Eligibility was limited to singleton term (37 + 0 weeks of gestation) pregnancies with intact membranes, within the active phase of labor defined as cervical dilatation between 4 and 9 cm. The study was approved by the local institutional review board, and all women provided written informed consent prior to participating in the study. Study design
Downloaded by [Universite Laval] at 00:37 10 October 2015
J Matern Fetal Neonatal Med, 2015; 28(14): 1633–1636
Women in active phase of labor with intact membranes were connected to EUM. In addition, all women were monitored by external tocodynamometer and electronic fetal heart rate monitoring, which are routinely used in all deliveries. All decisions regarding labor management including the frequency of cervical dilatation examination, need for oxytocin for augmentation or dosage changing, or artificial rupture of membranes (AROM) timing were made solely by the attending physician and were based on the routinely used external tocodynamometer and other clinical signs and symptoms. The attending physician and research team were blinded to the EUM results. Women who were augmented with oxytocin but had dosage changes during EUM monitoring period were subsequently excluded from final analysis. Data collection The following data were collected for each participant: demographic and obstetric characteristics, administration of oxytocin, cervical dynamics during EUM monitoring period and EUM recordings. The EUM device A novel EMG device, EUM-100 (OB-Tools Ltd, MigdalHaemek, Israel), was used to measure the electrical uterine activity. The system is comprised of a multichannel surface electromyogram, a three-dimensional position sensor and a personal computer providing data analysis and a graphical user interface. The EUM signals are acquired and amplified using a proprietary isolated amplifier box based on modified Teledyne A0401 modules (Teledyne Inc, Thousand Oaks, CA). The surface EUM activity is acquired by nine electrodes evenly placed on the patient’s abdomen and a tenth common ground electrode on the patient’s left thigh. The measurement of EUM signals together with their physical location provides an accurate estimation of the uterine activity in the three-dimensional space. The electrical signal from the myometrium is recorded and processed using a uterine contractility algorithm. Uterine muscle activity is quantified using the EUM scoring index which is defined as the mean electrical activity of the uterine muscle over a period of 10 min and is measured in units of micro-Joule (micro-Watt-Second, mWS) with an automatic data analyzer blinded to clinical outcome.
Results Overall, 37 women with singleton pregnancies at term were enrolled. The demographic and obstetrical characteristics are presented in Table 1. Mean maternal age was 30.8 ± 4.5 years and 24% were nulliparous. Eleven women were evaluated for more than 100 min. Mean EUM-index at the first 10 min of the exam (EUM1) for all women was 3.3 ± 0.6mWS, and was referred as baseline. Sixty-five cervical dilatation examinations during active phase of labor prior to membranes’ rupture were analyzed. Thirty-two (68%) women had more than one cervical dilatation measurement. In a stepwise linear regression model accounting for maternal age, gravity, parity, gestational age, BMI, previous cesarean delivery status, cervical dilatation and the use of oxytocin in labor, EUM was significantly affected by cervical dilatation (p ¼ 0.005, Figure 1), maternal age (p ¼ 0.04) and previous cesarean delivery status (p ¼ 0.02). In a repeated measurement, a non-parametric Fridman’s test for all subjects who have had at least 10 continues EUM measurements was performed (N ¼ 11). There was a significant increase in electrical uterine activity as labor progressed (p ¼ 0.01, Figure 2).
Discussion In the current study, we prospectively assessed factors affecting uterine electrical activity during active phase of Table 1. Demographic and obstetrical characteristics of the study group.
Variable
Study group (n ¼ 37)
Maternal age (years) Gestational age (weeks) Gravidity Parity Nulliparity Previous CS BMI at admission (kg/m2) Oxytocin use during labory Number of cervical dilatation measurements per patient 1 2 3 Duration of EUM monitoring (min)* Duration 4100 min*
30.8 ± 4.5 39.2 ± 1.0 2.7 ± 1.3 1.4 ± 1.0 9 (24.3%) 3 (8.1%) 26.8 ± 3.9 16 (43.2%) 1.8 ± 0.6 12 (32.4%) 22 (59.5%) 3 (8.1%) 98.1 ± 60.0 11 (44%)
Data are presented as mean ± SD or n (%). *Among 25 women with at least two cervical dilatation measurements. yNo change in oxytocin dosage during EUM monitoring period. BMI, body mass index; CS, cesarean section; EUM, electrical uterine myography.
DOI: 10.3109/14767058.2014.964677
Downloaded by [Universite Laval] at 00:37 10 October 2015
labor prior to membranes’ rupture using novel EUM technology. Our main findings were: (1) Overall, EUMindex (uterine activity) is enhanced with increase in cervical dilation during the active phase as labor progresses. (2) Previous cesarean delivery status and lower maternal age is associated with higher uterine activity. BMI was not significantly associated with EUM-index. The traditional methods for assessment of uterine contraction intensity are limited. Intrauterine pressure catheter necessitates ruptured membranes prior to application. Moreover, the method is invasive and thus has potential for complications. The technology of EUM used in the current study and its non-invasive nature, enabled performing quantification of uterine contractions intensity in the active phase while membranes are intact. Previous study from our group [14] has demonstrated that myometrial electrical activity recorded by the EUM is significantly enhanced following AROM. Thus, to avoid confounders, we measured uterine
Figure 1. The association between EUM-index and cervical dilatation during the active phase of labor. Data represent EUM-index results at the time of 65 cervical dilatation examinations during active phase labor prior to membranes’ rupture of 32 women. Figure 2. The change in mean EUM measurement during 10 consecutive measurements (a period of 100 min). Borders represent 95% confidence interval.
Uterine electrical activity in the active phase
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activity in the active phase only prior to rupture of membranes. Recent studies focused on quantification of uterine activity during labor [1,15–17]. Still, though outdated evidence exist regarding an increase in uterine activity during labor [18], information on the different intensities of uterine activity through the progress of active phase itself is lacking. Our data may suggest that enhanced electrical myometrial activity through the active phase, may, in part, be responsible for adequate progress in labor. In clinical practice, this may shed light on the mechanisms for pathological progress of labor and be a future therapeutic target. Other than cervical dilation, maternal age was also inversely correlated with EUM-index. It was suggested that older age is associated with a significant decrease in contractility for spontaneous contractions, but only in the non-pregnant state [19]. In the pregnant myometrium, a wide range of contractile ability was found between women and little evidence for decreased spontaneous activity appeared between the ages of 25 and 40. The lack of difference in the pregnant state over this period was attributed to the response to gestational hormones. On the other hand, other studies suggested that advanced maternal age is associated with increase in operative vaginal deliveries, cesarean section, and an increased need for oxytocin-augmentation [20,21]. These findings were shown not to be explained by co-morbidities such as obesity or gestational diabetes. One hypothesis proposed for these findings is that with increasing age, the myometrium is less effective or less responsive to uterotonic agents such as oxytocin or prostaglandins thereby indicating a direct effect of aging on myometrial function [20]. Uterine electrical activity recorded with EUM in our study is in concordance with this hypothesis. Moreover, our results might suggest that uterine activity in women with previous cesarean section is even enhanced. Previous study [22] measuring in vitro myometrial contractility, found that myometrium from women whose previous cesarean section was for fetal distress contracted with more force than that from women whose previous cesarean section was necessary because of other indications. However, our sample size is too small to separate the various indications.
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Previous studies have also found poor spontaneous and oxytocin-stimulated uterine contractility in vitro in postdate pregnancies [23] and obese women [24]. Our study did not confirm these observations. It is possible that the mechanical contractile ability of the myometrium tested in these studies does not necessarily equal electrical activity. Moreover, these studies were made in vitro and there is a possibility that other factors play a role in the in vivo environment that influence the contractility and mask its effect, possibly hormonal effects. The prospective nature of our design and the blinding of both treating physician and research team to EUM measurements during labor as well as blinding of the data analyzer to clinical results strengthen our findings, Still, our study has several limitations. The study was done on a small number of patients. Larger studies are needed to confirm our findings. Since this was an observational study rather than an interventional one, we lacked a control arm. Moreover, as labor was managed by the treating physician, some of the participants had been administered oxytocin prior to recruitment. However, oxytocin dosage was not altered during the reported hour of assessment, which minimizes its bias effect. In conclusion, we demonstrated that electrical uterine activity during the active phase of labor prior to rupture of membranes is affected by cervical dilatation, maternal age, and previous cesarean delivery status. Moreover, electrical uterine activity is enhanced throughout labor. Further research is warranted in order to describe electrical uterine activity in pathological labors for better future clinical purposes.
Declaration of interest The authors report no conflict of interest.
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