A Comparison of Surface Acquired Uterine Electromyography and Intrauterine Pressure Catheter to Assess Uterine Activity Gabi Haran, MD; Michal Elbaz, MD; Moshe D

Research www.AJOG.org

OBSTETRICS A comparison of surface acquired uterine electromyography and intrauterine pressure catheter to assess uterine activity Gabi Haran, MD; Michal Elbaz, MD; Moshe D. Fejgin, MD; Tal Biron-Shental, MD

OBJECTIVE: Intrauterine pressure catheter (IUPC) is the primary device RESULTS: The correlation of the frequency, intensity, and tone of con- used to evaluate uterine activity. In contrast to the IUPC, electrical uter- tractions between uterine electromyography and IUPC was strong with ine myography (EUM) enables noninvasive measurement of frequency, signiﬁcant r values of 0.808-1 (P Ͻ .0001). intensity, and tone of contractions. The aim of this study was to determine the accuracy of EUM compared to IUPC. CONCLUSION: Electrical uterine electromyography yields information STUDY DESIGN: EUM measured myometrial electrical activity using a about uterine contractility comparable to that obtained with IUPC. multichannel ampliﬁer and a noninvasive position sensor. In all, 47 women in labor were monitored simultaneously with an IUPC and EUM. We compared the frequency, intensity, and tone of uterine contractions Key words: contractions, intrauterine pressure catheter, myometrial between the methods. electrical activity

Cite this article as: Haran G, Elbaz M, Fejgin MD, et al. A comparison of surface acquired uterine electromyography and intrauterine pressure catheter to assess uterine activity. Am J Obstet Gynecol 2012;206:412.e1-5.

onitoring uterine activity during dynamometry is limited by the thickness of clinical trial of internal and external Mlabor is indicated for evaluating the abdominal wall and by its position rel- monitoring did not show any differ- labor progress and the diagnosis of uter- ative to the uterus.4,5 ence in the rate of operative deliveries ine tachysystole, which poses a potential The intrauterine pressure catheter or of adverse neonatal outcomes.12-14 risk of fetal distress.1-3 (IUPC) is considered to be the gold Myometrial activity resulting in con- Tocodynamometry has long been the standard for monitoring uterine contractions is the result of molecular changes most common method for assessing uter- tractions as it enables assessment of that lead to increased coupling and excitabil- ine contractility during labor. Although both the frequency and the intensity of ity of cells.15-19 Electrical activity of the myo- this method has no complications and en- contractions more accurately than to- metrium can be monitored noninvasively 6-8 ables measurement of the frequency and codynamometry. However, IUPC by uterine electromyography (EMG).19-21 duration of contractions, its major limita- requires ruptured membranes prior to Electrical uterine myography (EUM) tion is the inability to assess the intensity of catheter insertion; therefore, its use is monitoring uses an EMG monitor with 9 uterine contractions, which is crucial for limited. In addition, this invasive electrodes that are placed on the maternal labor management. The accuracy of toco- method carries risks of placental and abdominal surface to evaluate uterine con- fetal damage, infection, and uterine tractions. Not only does EUM enable non- perforation.9-11 From the Department of Obstetrics and invasive evaluation of the beginning, time The American College of Obstetricians Gynecology, Maternal Fetal Unit, Meir Medical to peak, duration and frequency of and Gynecologists and the Society of Ob- Center, Kfar Saba, afﬁliated with the Sackler uterine contractions, it also evaluates School of Medicine, Tel Aviv University, Tel stetricians and Gynecologists of Canada Aviv, Israel. recommend the use of IUPC in selected their intensity. Furthermore, since it is Received Aug. 7, 2011; revised Oct. 28, 2011; circumstances, such as maternal obesity or noninvasive and does not require rup- accepted Dec. 15, 2011. limited response to oxytocin. The theory tured membranes, it can be used as a M.D.F. is an unpaid professional adviser to OB behind these recommendations is that diagnostic tool for uterine contrac- Tools, Yokne’am, Israel. The other authors tions in suspected preterm labor. It report no conﬂict of interest. monitoring with IUPC might improve both maternal and fetal outcomes by al- also allows ambulation during moni- Reprints: Tal Biron-Shental, MD, Department toring. EUM has been shown to corre- of Obstetrics and Gynecology, Meir Medical lowing better adjustment of oxytocin, thus Center, 59 Tchernichovsky St., Kfar Saba preventing uterine hyperstimulation and spond strongly with tocodynamomet- 44821, Israel. [email protected]. fetal hypoxia, or by enabling better inter- ric sensor in measuring contractions 19,22 0002-9378/$36.00 pretation of abnormal fetal heart rate pat- and predicting preterm labor. © 2012 Mosby, Inc. All rights reserved. terns in relation to uterine activity. This The aim of this study was to compare doi: 10.1016/j.ajog.2011.12.015 hypothesis is mainly based on expert EUM and IUPC monitoring in terms of See Journal Club, page 449 opinion, as limited clinical data are onset, time to peak, duration, frequency, available to support it. A randomized and intensity of uterine contractions.

412.e1 American Journal of Obstetrics & Gynecology MAY 2012 www.AJOG.org Obstetrics Research

tions were compared. The data evalua- TABLE tor was blinded to the stage of labor Demographic and clinical characteristics of participants that was recorded, as well as to the out- .Parameter Range Average ؎ SD come of the labor Maternal BMI 20.2–41.6 30.31 Ϯ 4.626 IUPC was measured using millimeters ...... of mercury (mm Hg) and EUM, in ␮W. Gravity 1–11 3 Ϯ 2.77 ...... Evaluated parameters were the onset Parity 0–8 2 Ϯ 2.26 ...... of the contraction, its peak, time to na- Gestation 32 wk ϩ 4 d–42 wk ϩ 6 d 39 wk ϩ 4dϮ 2wkϩ 2d dir, the duration, and intensity of each ...... Initial cervical dilatation, cm 1–9.5 4.7 Ϯ 1.9 contraction. As accepted while using ...... IUPC, we also calculated the total eleva- Fetal weight, g 1490–4300 3261 Ϯ 584 tion of mm Hg above baseline in all con- ...... Mode of delivery No. of parturients Percentage tractions during 10 minutes (known as ...... Montevideo units) and the total ␮W Normal vaginal delivery 22 46.8 ...... during the 10 minutes measured by the Cesarean section 18 38.3 EUM. The novel software of the tested ...... Vacuum-assisted vaginal delivery 7 14.9 device created the waveform of the con- ...... tractions and enabled us to calculate the Augmentation of labor with oxytocin 40 ...... area under the curve of the contractions BMI, body mass index. that were detected by the new method in Haran. A comparison of intrauterine pressure catheters and electrical activity of the myometrium. Am J Obstet a similar way to the accepted evaluation Gynecol 2012. of Montevideo while using IUPC. We compared the ratios of these measure- MATERIALS AND METHODS difficulties with recording contractions ments in each participant. Since the units This prospective observational study was by the IUPC or after resolving the tech- used to evaluate the contractions are dif- carried out in a single institution, Meir nical difficulties were included in the ferent, we also calculated the area under Medical Center, Kfar Saba, Israel. study. the curve of the contractions and com- The inclusion criteria were singleton The study was approved by the national pared the correlation between the meth- pregnancy without evidence of signifi- Israel Ministry of Health Ethical Commit- ods for that term, as well. cant fetal malformations, patients Ͼ24 tee (approval no. 116-09) and registered in gestational weeks, in any stage of labor. the National Institutes of Health Clinical Statistical analysis All participants required IUPC for ac- Trials Registry (NCT1165879). All partici- The statistical analysis was performed cepted obstetrical indications such as pants signed an informed consent form. using software (SAS, version 9.2; SAS In- protracted labor or augmentation of la- stitute, Cary, NC). Student t test was bor for a multipara, or had an amnioin- Equipment used to evaluate the differences between fusion catheter inserted for repeated The EUM monitor is a novel technology the contraction parameters: the onset of variable decelerations. The catheter en- software and device developed by OB- the contraction, its peak, the time to na- abled evaluation of the contractions by Tools (Migdal Ha’emek, Israel). The de- dir, the duration, and the intensity as IUPC without further intervention. vice measures the electrical activity of the measured by the IUPC and EUM meth- Power analysis calculation for correla- uterus by using 9 surface EMG electrodes ods. Pearson analysis of coefficient was tion between the 2 methods indicated and a multichannel amplifier. The elec- used for correlations. that 41 participants were required to trodes are placed in a square surround- achieve an ␣ error of 0.05 and a ␤ error of ing the umbilicus, forming 3 rows and 0.9. Equivalence of the measurements columns. The location of the electrodes RESULTS was defined as a difference of up to 5 sec- is determined using a noninvasive posi- The study population included 47 partu- onds between the 2 methods (EUM and tion sensor. The energy of the contrac- rients in various stages of labor. The de- IUPC) regarding the onset and the dura- tions is presented in units of microwatts mographic and clinical characteristics of tion of the contraction, and Ͻ5% differ- (␮W). The 9 electrodes enable precise the participants are presented in the Ta- ence in the intensity of the contraction. measurements of the EMG from differ- ble. Uterine contractions were evaluated These values are based on the assump- ent areas of the uterus and the software simultaneously by EUM and IUPC. tions that the differences in the measures enables incorporation of the data and We faced technical difficulties in mon- have no clinical significance. analyzing them into a contraction wave. itoring contractions with IUPC in 7 pa- The use of an IUPC can present tech- In the current study, each partici- tients, all of which were resolved after nical challenges; therefore, for the sake of pant was monitored for 30 minutes si- some maneuvers such as washing or re- better comparison between IUPC and multaneously by EUM and by IUPC placing the catheter. No technical diffi- EUM, only patients without technical and the measurements of the contrac- culties were encountered with EUM. The

MAY 2012 American Journal of Obstetrics & Gynecology 412.e2 Research Obstetrics www.AJOG.org

final comparisons were done after reso- FIGURE lution of the technical difficulties. Contraction’s length by EUM vs IUPC Paired t test as well as Pearson analysis showed very high correlations between the EUM and the IUPC. There was a very strong correlation of the times the contractions began, reached their peak, and ended (P Ͻ .0001) (Figure, A). Correlation of contraction length was 0.904 (P Ͻ .0001) (Figure, B) and intensity was 0.80 (P Ͻ .0001) (Figure, C). The average ratios of the 10-minute calculation of mm Hg (Montevideo) measured by the IUPC and the total ␮W measured by the EUM for all the contractions evaluated in the study were 6.48 Ϯ 2.71, respectively, with no sig- nificant differences between the study participants. This reflects a consistent correlation between the different units used using the 2 systems for evaluating uterine contractions. The calculations of area under the curve in both methods showed an average correlation coefficient of 0.809 Ϯ 0.003 (P Ͻ .0001).

COMMENT In the current study, we found a very strong correlation between measurement of uterine contractions by EUM and IUPC. Our results demonstrate the accuracy of EUM in measuring the onset, time to peak, duration, and intensity of uterine contractions compared to IUPC measurements. The accepted method for A, Correlation between times from onset to peak of contractions between intrauterine pressure catheter measuring the intensity of uterine contrac- (IUPC) and electrical uterine myography (EUM). Correlations were calculated for all contractions detected tions is by IUPC using mm Hg units and during study period. B, Correlation between duration of contractions as measured by IUPC and EUM. 23 calculating Montevideo evaluation. The Correlations were calculated for all contractions detected during study period. Continued on the next page. excellent correlation between Montevideo Haran. A comparison of intrauterine pressure catheters and electrical activity of the myometrium. Am J Obstet Gynecol 2012. and the total ␮W during the 10-minute intervals and the area under the curves in both methods that was observed in the and intensity of contractions is even labor, but additional studies in that area current study supports the reliability of more critical when evaluating premature are required.19,27 EUM of uterine contractions. uterine contractions. It is well estab- Intrauterine pressure measurement is Accurate monitoring of uterine con- lished that prematurity is a leading cause considered the most objective way of mea- tractions curve is an essential part of the of fetal mortality and morbidity,25 yet suring uterine activity in labor, and in this cardiotocogram and should be obtained over half of preterm labor episodes do not respect it is superior to clinical assessment by the best method available. It might result in preterm births, meaning that or external tocography.28 However, there help to prevent fetal acidemia by detect- there is overtreatment and many unneces- are technical difﬁculties while using the ing excessive uterine activity during la- sary hospitalizations for premature uterine IUPC.29,30 In 14.85% of the cases in our bor.1-3,24 This is particularly important contractions and suspected preterm la- study, we had poor quality during part of during a protracted active phase of labor bor.26 Therefore, better tools for diagnos- the recordings, problems with balancing or induction of labor when knowledge of ing true preterm labor are essential. Previ- the baseline before measuring contrac- the intensity of the contractions is essen- ous preliminary studies have shown that tions, or difﬁculties with an occult or dis- tial for clinical decision making.5-7 Accu- measuring myometrial electrical activity placed catheter that had to be resolved rate assessment of frequency, duration, may help identify patients in true preterm prior to assessing uterine activity. We en-

412.e3 American Journal of Obstetrics & Gynecology MAY 2012 www.AJOG.org Obstetrics Research

on fetal oxygen status and fetal heart rate FIGURE patterns. Am J Obstet Gynecol 2008;199: Contraction’s length by EUM vs IUPC 34.e1-5. 4. Maul H, Maner WL, Olson G, Saade GR, Garfield RE. Noninvasive transabdominal uterine electromyography correlates with the strength of intrauterine pressure and is predictive of labor and delivery. J Matern Fetal Neonatal Med 2004;15:297-301. 5. Newman RB. Uterine contraction assessment. Obstet Gynecol Clin North Am 2005;32:341-67. 6. American College of Obstetricians and Gyne- cologists. Committee on Practice Bulletins- Obstetrics. Dystocia and augmentation of labor. Int J Gynaecol Obstet 2004;85:315-24. 7. Induction of labor: guideline no. 5. Utrecht (The Netherlands): Dutch Society of Obstetrics and Gynaecology; 2008. 8. Liston R, Sawchuck D, Young D. Fetal health surveillance: antepartum and intrapartum con- sensus guideline. J Obstet Gynaecol Can 2007; 29:S3-S56. Continued from the previous page. C, Correlation between contraction intensity measured by IUPC 9. Wilmink FA, Wilms FF, Heydanus R, Mol BW, and EUM were calculated by summing intensities of area under curves measured at 10-minute Papatsonis DN. Fetal complications after place- intervals, similar to accepted method of calculating Montevideo when using IUPC, and correlation ment of an intrauterine pressure catheter: a report of two cases and review of the literature. J between methods was calculated for all intervals. Matern Fetal Neonatal Med 2008;21:880-3. Haran. A comparison of intrauterine pressure catheters and electrical activity of the myometrium. Am J Obstet Gynecol 2012. 10. Madanes AE, David D, Cetrulo C. Major complications associated with intrauterine pressure monitoring. Obstet Gynecol 1982;59:389-91. countered no difficulties with the EUM, the contractions follow an upward or a 11. Matsuo K, Lynch MA, Kopelman JN, Atlas which emphasizes another benefit of this downward propagation path. The device RO. Anaphylactoid syndrome of pregnancy im- method. Published data supports that elec- and software used in the current study mediately after intrauterine pressure catheter trohysterographic contraction detection enable an integration of EMG signals de- placement. Am J Obstet Gynecol 2008;198:e8-9. 12. Bakker JJH, Verhoeven CJM, Janssen PF, correlates with IUPC better than tocometry tected from 9 points of the uterus in a et al. Outcomes after internal versus external 31 in patients with high body mass index. way that enables not only an accurate tocodynamometry for monitoring labor. N Engl Given the high correlation between EUM evaluation of the beginning, peak, dura- J Med 2010;362:306-13. and IUPC that was shown in the current tion, and intensity of the contractions 13. Chia YT, Arulkumaran S, Soon SB, Nor- study, EUM may have an advantage over the but also an evaluation of the progression shida S, Ratnam SS. Induction of labor: does internal tocography result in better obstetric tocometry in overweight patients, as well. of the contraction wave and calculating outcome than external tocography. AustNZJ Transabdominal uterine EMG with the area under curve similar to the cur- Obstet Gynaecol 1993;33:159-61. technology that is similar to that of the rent evaluation of the Montevideo but in 14. Chua S, Kurup A, Arulkumaran S, Ratnam SS. EUM has been shown to correlate with a noninvasive technology. Augmentation of labor: does internal tocography re- external tocomyometry and with IUPC. The qualities of the EUM make it suit- sult in better obstetric outcome than external tocography. Obstet Gynecol 1990;76:164-7. However, the number of patients ana- able for accurate evaluation of uterine con- 15. Garfield R, Maner W. Physiology and elec- lyzed was small and lacked statistical tractions. It is a potential diagnostic tool trical activity of uterine contractions. Semin Cell power to determine the accuracy of the for preterm labor, although further inves- Dev Biol 2007;18:289-95. method.15,30-32 Moreover, the wave tigation is needed to support this hypoth- 16. Tezuka N, Ali M, Chwalisz K, Garfield RE. curve was not described.15,27 The device esis. Based on the results of the current Changes in transcripts encoding calcium chan- nel subunits of rat myometrium during preg- and software used in the current study is study, we believe that EUM yields infor- nancy. Am J Physiol 1995;269:1008-17. capable of translation of the electrical mation about uterine contractility compa- 17. Young RC. Tissue-level signaling and con- signal into a contraction wave similar to rable to that obtained with IUPC. f trol of uterine contractility: the action potential- the gold standard of today, the IUPC, but calcium wave hypothesis. J Soc Gynecol Inves- in a noninvasive method with precise tig 2000;7:146-52. REFERENCES 18. Balducci J, Risek B, Gilula NB, Hand A, readings and without drawbacks of the 1. Bakker PC, Kurver PH, Kuik DJ, Van Geijn Egan JF, Vintzileos AM. Gap junction formation 29 IUPC such as blocking and kinking. HP. Elevated uterine activity increases the risk in human myometrium: a key to preterm labor. Better understanding of the contraction of fetal acidosis at birth. Am J Obstet Gynecol Am J Obstet Gynecol 1993;168:1609-15. wave was shown to be superior to only 2007;196:313.e1-6. 19. Lucovnik M, Maner WL, Chambliss LR, et detection of electrical signals also by Eu- 2. Bakker PC, Van Rijswijk S, van Geijn HP. al. Noninvasive uterine electromyography for 32 Uterine activity monitoring during labor. J Peri- prediction of preterm delivery. Am J Obstet Gy- liano et al, who mapped the uterine nat Med 2007;35:468-77. necol 2011;204:228e1-10. electrical signals in labors and identified 3. Simpson KR, James DC. Effects of oxytocin- 20. Marshall JM. Regulation of the activity in a center of uterine activity from where induced uterine hyperstimulation during labor uterine muscle. Physiol Rev 1962;42:213-27.

MAY 2012 American Journal of Obstetrics & Gynecology 412.e4 Research Obstetrics www.AJOG.org

21. Kuriyama H, Csapo A. A study of the partu- linked birth/infant death data set. Natl Vital Stat contractions: a dynamical approach. J Matern rient uterus with the microelectrode technique. Rep 2004;53:1-29. Fetal Neonatal Med 2003;14:8-21. Endocrinology 1967;80:748-53. 26. McPheeters ML, Miller WC, Hartmann KE, 30. Rabotti C, Mischi M, van Laar JO, Oei GS, 22. Garﬁeld RE, Maner WL. Uterine electro- et al. The epidemiology of threatened preterm Bergmans JW. Estimation of internal uterine myography in humans–contractions, labor, and labor: a prospective cohort study. Am J Obstet pressure by joint amplitude and frequency anal- delivery. Medicon 2007, IFMBE Proceedings, Gynecol 2005;192:1325-9. ysis of electrohysterographic signals. Physiol 2007;16:128-30. 27. Most O, Langer O, Kerner R, David GB, Cal- Meas 2008;29:829-41. 23. Calderyo-Barica R, Poseri JJ. Physiology of deron I. Can myometrial electrical activity iden- 31. Euliano TY, Nguyen MT, Marossero D, Ed- the uterine contraction. Clin Obstet Gynecol tify patients in preterm labor? Am J Obstet Gy- wards RK. Monitoring contractions in obese par- 1960;3:386-408. necol 2008;199:378.e1-6. turients. Obstet Gynecol 2007;109:1136-40. 24. Bakker PC, van Geijn HP. Uterine activity: 28. Gibb DM. Measurement of uterine activity in 32. Euliano TY, Marossero D, Nguyen MT, Eu- implications for the condition of the fetus. J Peri- labor–clinical aspects. Br J Obstet Gynaecol liano NR, Principe J, Edwards RK. Spatiotem- nat Med 2008;36:30-7. 1993;100(Suppl):28-31. poral electrohysterography patterns in normal 25. Mathews TJ, Menacker F, MacDorman MF. 29. Nagarajan R, Eswaran H, Wilson JD, Mur- and arrested labor. Am J Obstet Gynecol Infant mortality statistics from the 2002 period: phy P, Lowery C, Preissl H. Analysis of uterine 2009;200:54.e1-7.

412.e5 American Journal of Obstetrics & Gynecology MAY 2012