275
Schiff et al, Acoustic Stimulation test
j. Perinat. Med. 20(1992)275-279
Acoustic stimulation as a diagnostic test: comparison with oxytocin challenge test Eyal Schiff, Shlomo Lipitz, Eyal Sivan, Gad Barkai, and Shlomo Mashiach
The Department of Obstetrics and Gynecology, Sheba Medical Center, Sackler School of Medicine, Tel-Aviv University, Tel-Hashomer, Israel
1 Introduction
2 Patients and methods
Since publication of the early reports on fetal response to sound stimulation more than 50 years ago [3], a considerable amount of evidence has been accumulated, indicating that acceleration of the fetal heart rate in reaction to vibroacoustic stimulation is a reliable sign of fetal welfare, especially after the 28th week of gestation. However, in a review of studies on the use of fetal acoustic stimulation as a test of fetal well-being, it was concluded that the data are still inadequate and that additional clinical prospective trials are needed before acoustic stimulation becomes routinely included in the standard antenatal care [6]. In most of the clinical trials conducted so far, the effectiveness of an acoustic stimulation test (AST) in predicting fetal distress was compared with that of the standard non-stress test (NST). Only in one non-randomized trial did the authors compare the effectiveness of an AST with that of an oxytocin challenge test (OCT) and suggest that the AST might be a valuable screening measure to identify those patients who require further investigation and should therefore undergo an OCT [5]. The present prospective randomized controlled trial was undertaken in an attempt to determine: 1. the incidence of abnormal AST among fetuses demonstrating a non-reactive NST at term; 2. the influence of an AST on the result of the subsequent OCT; 3. the value of the AST, as compared with the OCT, as an indicator of fetal well-being at term pregnancies.
Enrolled in this study were pregnant woman at term (38 — 42 gestational week), with a non-complicated pregnancy, who were admitted to our delivery unit during a one year period, due to a non-reactive or suspicious routine NST at the time of admission. We defined a non-reactive NST as one lasting at least 40 minutes without a single fetal heart rate acceleration of 15 beats per minute (bpm) or more, for 15 seconds or more. We defined a suspicious NST as one with at least one late type deceleration of fetal heart rate, i.e., deceleration of more than 15 bpm for more than 15 seconds, started 30 or more seconds after the beginning of a spontaneous uterine contraction, and finished 30 or more seconds after the end of this contraction. Women at preterm or post-term, women with multiple pregnancy, and women with complications of pregnancy such as pregnancy-induced hypertension, diabetes, estimated fetal growth-retardation, placental abruption or placenta previa were not enrolled in this study. During a 14 month period 121 women who fulfilled the above criteria were enrolled in the study. These women were randomly divided on the basis of their citizenship identification number into one of two groups. The women in group A (n = 62) underwent an AST and then a subsequent OCT. The women in group B (n = 59) underwent only OCT, according to the accepted policy of our department in the case of a nonreactive or suspicious NST at term.
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276
Schiff et al, Acoustic stimulation test
For providing an AST, an electronic artificial larynx (Corometrics Medical Systems Inc., Model 146) was employed as previously used by others [1,8]. The stimulus was applied only once for five seconds, near by the fetal head, while the women is on a left lateral recumbent position. The fetal heart rate was continuously monitored. We defined a reactive AST when two or more fetal heart rate accelerations of 15 or more bpm, for 15 or more seconds, were recorded during the 20 minutes following the acoustic stimulation. OCT was carried out using intravenous oxytocin infusion starting with 2.5 mu/min rate and increasing by 2.5 mu/min every 20 minutes until a satisfaction OCT was accomplished i.e., three contractions observed in a ten minute interval. In cases of women with previous uterine operation we started with 1 mu/min infusion and increased by 1 mu/min each time. We defined an abnormal OCT as positive or suspicious one, i. e. as one demonstrating a fetal heart rate with late or variable type decelerations accompanied at least half of the uterine induced contractions. In order to evaluate the predictive efficacy of the tests we defined two criteria for unfavorable outcome of the tested fetuses: 1. Antenatal or intranatal mortality; 2. Fetal distress inlabor — labor heart rate monitor presents signs of fetal distress necessitating immediate delivery. 3 Results Table I presents the clinical characteristics of the women in the two groups. No differences were found between the groups regarding mean age, mean gravity and parity, mean gestational age, sex of the infants and mean birth weight.
Among the women in group A 14 (22.5%) had a non-reactive AST before OCT was performed. The rate of abnormal OCT was lower, however not significantly, among the patients in group A compared to those in group B: 9 (14.5%) Vs. 14 (23.7%) cases, p = 0.06, power of test = 0.95. All nine cases in group A who had an abnormal OCT demonstrated a non-reactive AST before the OCT. Table II presents the incidence of fetal distress during labor among the patients who underwent AST and/or OCT, and the properties of these two tests in predicting fetal distress among the study population. No case of antenatal or intranatal mortality was recorded among all 121 patients.
4 Discussion Some clinical trials in which AST and NST were compared, found a good correlation between the results as well as the predictive value of perinatal outcome of these two tests of the fetal well being [8, 9]. Other studies demonstrated shortened non-stress testing time as a result of the acoustic stimulation [7, 8]. Recent reports which investigated the relationship between intrapartum fetal acid-base status and fetal heart rate response to vibro-acoustic stimulation showed high predictiveness of normal pH in the case of reactive stimulation test [2, 4]. READ and MILLER were the first to suggest that the acoustic stimulation test could be a valuable screening test to select patients who required further testing with an OCT3. These researches performed paired OCT and AST to 39 pregnant women. All women in their group with reactive AST had a negative OCT, while about two thirds of patients with a
Table I. Clinical characteristics of women in the two study groups
Age (years) Gravidity Parity Gestational age (days) Birth weight (g) Fetal sex: Male Female
Group A (N = 62)
Group B (N = 59)
28.2 4.4 2.3 284 3307
28.8 4.2 2.2 285 3347
+ 3.7 + 1.9 + 1.1 + 6 ± 390
48.3% 51.7%
+ 4.2 + 2.0 + 0.9 + 5 ± 409
48.1% 51.9%
P value NS NS NS NS NS NS NS
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Schiff et al, Acoustic stimulation test
277
Table Π. Incidence of fetal distress during labor and the properties os the single test in predicting it
Non Reactive Reactive Sensitivity Specificity Positive predictive value Negative predictive value
AST (Total 62)
OCT (Total 121)
FD* (+)
FD* (+)
FD* (-)
10 4
13 94
7 1
FD* (-) 7 47
abnormal normal
71% 88% 44% 96%
88% 87% 50% 98%
* FD - Fetal distress
non-reactive AST had a positive or suspicious OCT. However, neither this study nor other studies have investigated the possible influence of the AST on the OCT subsequently performed, and the predictive value of the AST compared to that of the OCT as a second procedure after a nonreactive NST. In this study the patients with a non-reactive NST at term were divided into two randomized groups in order to find whether the AST would change the rate of abnormal results in a subsequent OCT. Although the number of abnormal OCT results was lower among those women who previously to OCT underwent an AST, this difference was not significant and thus we conclude that the AST by itself does not improve the results of the OCT in the case of the enduring fetus. Among the group of women who underwent both AST and OCT our results were in accordance with those of READ and MILLER — none of the 47 patients with a reactive AST had an abnormal OCT while nine of the 14 patients with a non-reactive AST had an abnormal OCT. Thus, the positive and negative predictive values of the AST in predicting an abnormal OCT were 64% and 100% respectively, while the sensitivity and specificity were 100% and 91% respectively. In this trial we also compared the properties of the AST as a single test among the group randomized to undergo both AST and OCT, to those of the OCT as a single test in both groups, as a predictor test for fetal distress in subsequent labor. The AST had a similar specificity and negative predictive values to those of the OCT,
but a somewhat improved sensitivity and positive predictive value. The only false negative case of the AST in our study, i.e. a case that had a reactive heart response toward the acoustic stimulation but subsequently demonstrated signs of severe fetal distress which needed abdominal delivery, actually was also a case of false negative OCT since he had a normal OCT immediately after the AST. Thus, we assume that in this specific case the intranatal distress was acute and this fetus was probably well while being tested 36 h before delivery. Although the safety of the AST in different sound intensity levels is not yet established, most physicians regard it as a relatively safe noninvasive test. Compared to the OCT it is easier, quicker and probably cheaper to perform, especially in the outpatient clinic. In addition, it may be safer than OCT in specific cases such as overdistended uterus, previously operated uterus, and prematurity. This trial demonstrate that the AST may play the role of second line procedure for evaluating the fetal well-being in case of non-reactive NST at term, with even better diagnostic properties than the traditional OCT. Thus, we suggest that in these cases the AST may replace the need for OCT, or at least may restrict the use of the OCT only to those cases with non-reactive AST after a previously non-reactive NST. However, because of the small samples size of our groups, these recomondations are based on preliminary results only, and further research and developments are expected in order to test the tool.
Abstract
The usefulness of an acoustic stimulation test as a ing a non-reactive fetal non-stress test at term. The marker of fetal well-being was evaluated in a random- women were randomly divided into two groups: those ized controlled study of 121 pregnant Brought women exhibitin theYork firstUniversity group (n Bobst = 62)Library underwent an acoustic stimto you by | New Technical Services J. Perinat. Med. 20 (1992)
Authenticated Download Date | 6/25/15 6:48 AM
278
Schiff et al, Acoustic stimulation test
ulation test immediately prior to an oxytocin challenge test, while those in the second (n = 59) underwent an oxytocin challenge test only. Fetal response to the acoustic stimulation was non-reactive in 22.5% of the women tested in the first group. The incidence of abnormal oxytocin challenge test among the women who were previously subjected to an acoustic stimulation was somewhat lower than among those who did not (14.5% vs. 23.7%), but the difference was not significant. In the prediction of an abnormal oxytocin challenge test, a non-reactive acoustic stimulation test
had a sensitivity of 100%, a positive predictive value of 64% and a specificity of 91%. As a single test for the prediction of fetal distress in labor (n = 62), the acoustic stimulation test had a specificity and a positive predictive value similar to those of the oxytocin challenge test (n = 121), and its sensitivity was even higher (88% vs. 71%). We conclude that the acoustic stimulation test is at least as reliable as the oxytocin challenge test in the evaluation of fetal well-being in women exhibiting a non-reactive non-stress test at term.
Keywords: Acoustic stimulation test, Oxytocin. Zusammenfassung Vergleich von akustischer Stimulation und Oxytocinbelastung zur Vorhersage eines fetalen Distress am Termin
Die Akzeleration der fetalen Herzfrequenz nach vibroakustischer Stimulation ist insbesondere nach der 28. Woche ein zuverlässiger Parameter bei der fetalen Zustandsdiagnostik. In den meisten klinischen Studien wurde die Aussagekraft eines akustischen Stimulationstest (AST) im Hinblick auf ein fetales Distress mit dem normalen Non-stress-Test (NST) verglichen. Bei der vorliegenden randomisierten Versuchsreihe, die prospektiv angelegt wurde, wollten wir prüfen 1. wie häufig ein pathologischer AST bei Feten am Termin ist, die auch im NST nicht reagierten, 2. ob ein AST das Ergebnis eines nachfolgenden OBT beeinflußt und 3. die Aussagekraft des AST im Vergleich mit dem OBT im Hinblick auf den fetalen Zustand am Termin. 121 Frauen am Termin (38—42 Schwangerschaftswochen), die einen unkomplizierten Schwangerschaftsver-. lauf hatten und wegen eines routinemäßig durchgeführten non-reaktiven oder verdächtigen NST innerhalb eines Jahres zu uns überwiesen wurden, nahmen an der Studie teil. Die Frauen wurden anhand ihrer Personalausweisnummer 2 Gruppen zufallsmäßig zugeordnet. Gruppe A (n = 62) erhielt einen AST und im Anschluß daran einen OBT. Bei den Frauen der Gruppe B (n = 59) wurde lediglich ein OBT durchgeführt. In der Gruppe A hatten 14 Frauen (22,5%) einen non-reaktiven AST vor dem OBT. Abnorme OBT's traten in der Gruppe A nicht so häufig auf wie in der Gruppe B (9 Fälle = 14,5% vs. 14 Fälle = 23,7%), jedoch war der Unterschied nicht signifikant. Alle 9 Frauen der Gruppe A mit einem patho-
logischen OBT hatten einen non-reaktiven AST vor dem OBT. Tab. 2 zeigt die Häufigkeit eines fetalen Distress unter der Geburt bei den Patientinnen, die einen AST und/oder OBT erhalten hatten sowie die prädikativen Werte dieser beiden Tests im Hinblick auf ein fetales Distress in dem untersuchten Kollektiv. Ein antenataler oder intrapartualer Todesfall trat bei den 121 Patienten nicht auf. Suspekte OBT's waren bei Frauen, die vor dem OBT einen AST hatten, nicht so häufig, jedoch war der Unterschied nicht signifikant. Wir glauben daher nicht, daß der AST die Ergebnisse des OBT bei beeinträchtigten Feten verbessert. Die positiven und negativen prädikativen Werte des AST im Hinblick auf einen auffalligen OBT betrugen 64% bzw. 100%, während die Sensitivität bei 100% und die Spezifität bei 91% lagen. Vergleicht man nun die Aussagekraft des AST allein mit der Aussagekraft des OBT allein bei den Frauen, wo nach Randomisierung AST und OBT durchgeführt wurden, so zeigt sich, daß AST und OBT im Hinblick auf ein fetales Distress eine vergleichbare Spezifität und vergleichbare negative prädiktive Werte haben. Die Sensitivität und der positive prädiktive Wert sind jedoch beim AST besser. Unsere Studie zeigt, daß der AST als zweites Verfahren beim non-teaktiven NST am Termin zur fetalen Zustandsdiagnostik eingesetzt werden kann, da er sich mindestens ebenso gut eignet wie der traditionelle OBT. Darüberhinaus ist der AST einfacher und schneller durchzuführen, speziell bei ambulanten Patientinnen. Schließlich ist er auch billiger.
Schlüsselwörter: Belastungstest durch akustische Stimulation, Oxytocin.
Resume
fiable de bonne sante foetale, tout particulierement apres la 28eme semaine de grossesse. Dans de nombreux essais cliniques realises de la sorte, l'efficacite U acceleration du rythme cardiaque foetal, en reaction d'un test de Stimulation acoustique (TSA) pour predire Brought to you | New York Universityfoetale BobstaLibrary Technical Services la souffrance ete comparee avec le non-stress ä une Stimulation vibro-acoustique, represente unby signe
Test de stimulation acoustique pour prevoir de facon fiable la souffrance fatale, comparaison avec le test a l'ocytocine a terme
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J. Perinat. Med. 20 (1992)
279
Schiff et al, Acoustic stimulation test test standard (NST). Get essai controle randomise et prospectif a ete realise pour essayer de determiner: 1) Pincidence d'un TSA anormal chez les foetus presentant un NST non-reactif ä terme; 2) 1'influence d'un TSA sur le resultat d'un test ä l'ocytocine (TO) ulterieur; 3) la valeur du TSA, en comparaison avec le TO, comme indicateur du bien etre foetal au cours des grossesse a terme. 121 femmes enceintes, ä terme (38—42 semaines), avec une grossesse non compliquee, et qui ont ete admises dans notre centre d'accouchement, sur une periode d'un an, en raison d'un non-stress test de routine non-reactif ou suspect au moment de 1'admission, ont ete incorporees dans cette etude. Ces femmes ont ete divisees, de fagon randomisee, sur la base de leur nombre d'identification de citoyennete, en deux groupes. Les femmes du groupe A (n = 62) ont subi un TSA et ensuite un TO. Les femmes du groupe B (n = 59) n'ont subi qu'un TO. Parmi les femmes du groupe A, 14 (22,5%) presentaient un TSA non-reactif avant le TO. Le taux de TO anormaux etait inferieur, mais pas de fagon significative, chez les patientes du groupe A (9 cas, 14,5%), en comparaison avec celles du groupe B (14 cas, 23,7%). Les neufs cas du groupe A qui presentaient un TO anormal avaient un TSA non-reactif avant le TO. Le tableau 2 presente 1'incidence de la souffrance foetale au cours du travail chez les patientes ay ant benefice d'un TSA et/ou d'un TO, ainsi que la capacite de ces deux tests a predire la souffrance foetale parmi la population etudiee. II n'y a pas eu de cas de mortalite antenatale ni per-partum, chez les 121 patientes.
Bien que le nombre de resultats de TO anormaux soit inferieur chez les femmes ayant eu, avant le TO, un TSA cette difference n'est pas significative et, ainsi, nous concluons que le TSA, en soi, n'ameliore pas les resultats du TO. Les valeurs predictives positives et negatives du TSA pour la prediction d'un TO anormal sont, respectivement de 64% et de 100%, tandis que la sensibilite et la specificite sont respectivement de 100% et de 91%. Si compare les capacites du TSA, en tant que test unique, dans le groupe randomise pour subir les deux tests, TSA et TO, aux capacites du TO, en tant que test unique, dans les deux groupes, pour prevoir la souffrance foetale au cours du travail culterieur, nous trouvons que le TSA a une specificite et une valeur predictive negratives similaire ä celles du TO, mais une sensibilite et une valeur predictive quelque peu augmentees. Get essai demontre que le TSA peut jouer le role d'examen de seconde intention pour revaluation du bien etre foetal lorsque le NST n'est pas reactif, ä terme, avec en prime de meilleures capacites diagnostiques que le traditionnel TO. En outre, en comparaison avec le TO, le TSA est plus aise, plus rapide et vraissemblablement moins eher ä realiser, etb cela tout particulierement chez les patientes en ambulatoire. Aussi suggerons nous que, dans ces cas, le TSA puisse remplacer le TO, ou du moins limiter les indications du TO uniquement aux cas avec un TSA non-reactif, apres un NST anterieur non-reactif.
Mots-cles: Ocytocine, test de stimulation acoustique.
References
[7] SMITH CV, JP PHELAN, RH PAUL et al: Fetal [1] BIRNHOLTZ JC, BR BENACERRAF: The developacoustic stimulation testing: A retrospective exment of human fetal hearing. Science 222 (1983) perience with the fetal acoustic stimulation test. 516 Am J Obstet Gynecol 153 (1985) 567 [2] INGEMARSSON I, S ARULKUMARAN: Reactive fetal [8] SMITH CV, JP PHELAN, LD PLATT et al: Fetal heart rate response to vibroacoustic stimulation acoustic stimulation testing. II. A randomized cliin fetuses with low scalp blood pH. Br J Obstet nical comparison with the nonstress test. Am J Gynecol 96 (1989) 562 [3] PEIPER A: Sinnesempfindungen des Kindes vor Obstet Gynecol 155 (1986) 131 [9] WESTGREN M, H ALMSTROM, M NYMAN, U ULMseiner Geburt. Monatsschr Kinderheilkad 29 STEM: Maternal perception of sound-provoked fe(1925) 236 [4] POLZIN GB, KJ BLAKEMORE, RH PETREE, E AMON: tal movements as a measure of fetal well-being. Fetal vibro-acoustic stimulation: Magnitude and Br J Obstet Gynecol 94 (1987) 523 duration of fetal heart rate accelerations as a marker of fetal health. Obstet Gynecol 72 (1988) Received July 14, 1991. Revised January 24, 1992. 621 Accepted February 4, 1992. [5] READ JA, FC MILLER: Fetal heart rate acceleration in response to acoustic stimulation as a meaEyal Schiff, M. D. sure of fetal well-being. Am J Obstet Gynecol 129 Dept. Obstet. & Gynecol. (1977) 512 Sheba Medical Center [6] ROMERO R, M MAZOR, JC HOBBINS: A critical Tel-Hashomer 52621 appraisal of fetal acoustic stimulation as an anIsrael tenatal test for fetal well-being. Obstet Gynecol 71 (1988) 781 Brought to you by | New York University Bobst Library Technical Services J. Perinat. Med. 20 (1992)
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Schiff et al, Acoustic Stimulation test
j. Perinat. Med. 20(1992)275-279
Acoustic stimulation as a diagnostic test: comparison with oxytocin challenge test Eyal Schiff, Shlomo Lipitz, Eyal Sivan, Gad Barkai, and Shlomo Mashiach
The Department of Obstetrics and Gynecology, Sheba Medical Center, Sackler School of Medicine, Tel-Aviv University, Tel-Hashomer, Israel
1 Introduction
2 Patients and methods
Since publication of the early reports on fetal response to sound stimulation more than 50 years ago [3], a considerable amount of evidence has been accumulated, indicating that acceleration of the fetal heart rate in reaction to vibroacoustic stimulation is a reliable sign of fetal welfare, especially after the 28th week of gestation. However, in a review of studies on the use of fetal acoustic stimulation as a test of fetal well-being, it was concluded that the data are still inadequate and that additional clinical prospective trials are needed before acoustic stimulation becomes routinely included in the standard antenatal care [6]. In most of the clinical trials conducted so far, the effectiveness of an acoustic stimulation test (AST) in predicting fetal distress was compared with that of the standard non-stress test (NST). Only in one non-randomized trial did the authors compare the effectiveness of an AST with that of an oxytocin challenge test (OCT) and suggest that the AST might be a valuable screening measure to identify those patients who require further investigation and should therefore undergo an OCT [5]. The present prospective randomized controlled trial was undertaken in an attempt to determine: 1. the incidence of abnormal AST among fetuses demonstrating a non-reactive NST at term; 2. the influence of an AST on the result of the subsequent OCT; 3. the value of the AST, as compared with the OCT, as an indicator of fetal well-being at term pregnancies.
Enrolled in this study were pregnant woman at term (38 — 42 gestational week), with a non-complicated pregnancy, who were admitted to our delivery unit during a one year period, due to a non-reactive or suspicious routine NST at the time of admission. We defined a non-reactive NST as one lasting at least 40 minutes without a single fetal heart rate acceleration of 15 beats per minute (bpm) or more, for 15 seconds or more. We defined a suspicious NST as one with at least one late type deceleration of fetal heart rate, i.e., deceleration of more than 15 bpm for more than 15 seconds, started 30 or more seconds after the beginning of a spontaneous uterine contraction, and finished 30 or more seconds after the end of this contraction. Women at preterm or post-term, women with multiple pregnancy, and women with complications of pregnancy such as pregnancy-induced hypertension, diabetes, estimated fetal growth-retardation, placental abruption or placenta previa were not enrolled in this study. During a 14 month period 121 women who fulfilled the above criteria were enrolled in the study. These women were randomly divided on the basis of their citizenship identification number into one of two groups. The women in group A (n = 62) underwent an AST and then a subsequent OCT. The women in group B (n = 59) underwent only OCT, according to the accepted policy of our department in the case of a nonreactive or suspicious NST at term.
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276
Schiff et al, Acoustic stimulation test
For providing an AST, an electronic artificial larynx (Corometrics Medical Systems Inc., Model 146) was employed as previously used by others [1,8]. The stimulus was applied only once for five seconds, near by the fetal head, while the women is on a left lateral recumbent position. The fetal heart rate was continuously monitored. We defined a reactive AST when two or more fetal heart rate accelerations of 15 or more bpm, for 15 or more seconds, were recorded during the 20 minutes following the acoustic stimulation. OCT was carried out using intravenous oxytocin infusion starting with 2.5 mu/min rate and increasing by 2.5 mu/min every 20 minutes until a satisfaction OCT was accomplished i.e., three contractions observed in a ten minute interval. In cases of women with previous uterine operation we started with 1 mu/min infusion and increased by 1 mu/min each time. We defined an abnormal OCT as positive or suspicious one, i. e. as one demonstrating a fetal heart rate with late or variable type decelerations accompanied at least half of the uterine induced contractions. In order to evaluate the predictive efficacy of the tests we defined two criteria for unfavorable outcome of the tested fetuses: 1. Antenatal or intranatal mortality; 2. Fetal distress inlabor — labor heart rate monitor presents signs of fetal distress necessitating immediate delivery. 3 Results Table I presents the clinical characteristics of the women in the two groups. No differences were found between the groups regarding mean age, mean gravity and parity, mean gestational age, sex of the infants and mean birth weight.
Among the women in group A 14 (22.5%) had a non-reactive AST before OCT was performed. The rate of abnormal OCT was lower, however not significantly, among the patients in group A compared to those in group B: 9 (14.5%) Vs. 14 (23.7%) cases, p = 0.06, power of test = 0.95. All nine cases in group A who had an abnormal OCT demonstrated a non-reactive AST before the OCT. Table II presents the incidence of fetal distress during labor among the patients who underwent AST and/or OCT, and the properties of these two tests in predicting fetal distress among the study population. No case of antenatal or intranatal mortality was recorded among all 121 patients.
4 Discussion Some clinical trials in which AST and NST were compared, found a good correlation between the results as well as the predictive value of perinatal outcome of these two tests of the fetal well being [8, 9]. Other studies demonstrated shortened non-stress testing time as a result of the acoustic stimulation [7, 8]. Recent reports which investigated the relationship between intrapartum fetal acid-base status and fetal heart rate response to vibro-acoustic stimulation showed high predictiveness of normal pH in the case of reactive stimulation test [2, 4]. READ and MILLER were the first to suggest that the acoustic stimulation test could be a valuable screening test to select patients who required further testing with an OCT3. These researches performed paired OCT and AST to 39 pregnant women. All women in their group with reactive AST had a negative OCT, while about two thirds of patients with a
Table I. Clinical characteristics of women in the two study groups
Age (years) Gravidity Parity Gestational age (days) Birth weight (g) Fetal sex: Male Female
Group A (N = 62)
Group B (N = 59)
28.2 4.4 2.3 284 3307
28.8 4.2 2.2 285 3347
+ 3.7 + 1.9 + 1.1 + 6 ± 390
48.3% 51.7%
+ 4.2 + 2.0 + 0.9 + 5 ± 409
48.1% 51.9%
P value NS NS NS NS NS NS NS
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Schiff et al, Acoustic stimulation test
277
Table Π. Incidence of fetal distress during labor and the properties os the single test in predicting it
Non Reactive Reactive Sensitivity Specificity Positive predictive value Negative predictive value
AST (Total 62)
OCT (Total 121)
FD* (+)
FD* (+)
FD* (-)
10 4
13 94
7 1
FD* (-) 7 47
abnormal normal
71% 88% 44% 96%
88% 87% 50% 98%
* FD - Fetal distress
non-reactive AST had a positive or suspicious OCT. However, neither this study nor other studies have investigated the possible influence of the AST on the OCT subsequently performed, and the predictive value of the AST compared to that of the OCT as a second procedure after a nonreactive NST. In this study the patients with a non-reactive NST at term were divided into two randomized groups in order to find whether the AST would change the rate of abnormal results in a subsequent OCT. Although the number of abnormal OCT results was lower among those women who previously to OCT underwent an AST, this difference was not significant and thus we conclude that the AST by itself does not improve the results of the OCT in the case of the enduring fetus. Among the group of women who underwent both AST and OCT our results were in accordance with those of READ and MILLER — none of the 47 patients with a reactive AST had an abnormal OCT while nine of the 14 patients with a non-reactive AST had an abnormal OCT. Thus, the positive and negative predictive values of the AST in predicting an abnormal OCT were 64% and 100% respectively, while the sensitivity and specificity were 100% and 91% respectively. In this trial we also compared the properties of the AST as a single test among the group randomized to undergo both AST and OCT, to those of the OCT as a single test in both groups, as a predictor test for fetal distress in subsequent labor. The AST had a similar specificity and negative predictive values to those of the OCT,
but a somewhat improved sensitivity and positive predictive value. The only false negative case of the AST in our study, i.e. a case that had a reactive heart response toward the acoustic stimulation but subsequently demonstrated signs of severe fetal distress which needed abdominal delivery, actually was also a case of false negative OCT since he had a normal OCT immediately after the AST. Thus, we assume that in this specific case the intranatal distress was acute and this fetus was probably well while being tested 36 h before delivery. Although the safety of the AST in different sound intensity levels is not yet established, most physicians regard it as a relatively safe noninvasive test. Compared to the OCT it is easier, quicker and probably cheaper to perform, especially in the outpatient clinic. In addition, it may be safer than OCT in specific cases such as overdistended uterus, previously operated uterus, and prematurity. This trial demonstrate that the AST may play the role of second line procedure for evaluating the fetal well-being in case of non-reactive NST at term, with even better diagnostic properties than the traditional OCT. Thus, we suggest that in these cases the AST may replace the need for OCT, or at least may restrict the use of the OCT only to those cases with non-reactive AST after a previously non-reactive NST. However, because of the small samples size of our groups, these recomondations are based on preliminary results only, and further research and developments are expected in order to test the tool.
Abstract
The usefulness of an acoustic stimulation test as a ing a non-reactive fetal non-stress test at term. The marker of fetal well-being was evaluated in a random- women were randomly divided into two groups: those ized controlled study of 121 pregnant Brought women exhibitin theYork firstUniversity group (n Bobst = 62)Library underwent an acoustic stimto you by | New Technical Services J. Perinat. Med. 20 (1992)
Authenticated Download Date | 6/25/15 6:48 AM
278
Schiff et al, Acoustic stimulation test
ulation test immediately prior to an oxytocin challenge test, while those in the second (n = 59) underwent an oxytocin challenge test only. Fetal response to the acoustic stimulation was non-reactive in 22.5% of the women tested in the first group. The incidence of abnormal oxytocin challenge test among the women who were previously subjected to an acoustic stimulation was somewhat lower than among those who did not (14.5% vs. 23.7%), but the difference was not significant. In the prediction of an abnormal oxytocin challenge test, a non-reactive acoustic stimulation test
had a sensitivity of 100%, a positive predictive value of 64% and a specificity of 91%. As a single test for the prediction of fetal distress in labor (n = 62), the acoustic stimulation test had a specificity and a positive predictive value similar to those of the oxytocin challenge test (n = 121), and its sensitivity was even higher (88% vs. 71%). We conclude that the acoustic stimulation test is at least as reliable as the oxytocin challenge test in the evaluation of fetal well-being in women exhibiting a non-reactive non-stress test at term.
Keywords: Acoustic stimulation test, Oxytocin. Zusammenfassung Vergleich von akustischer Stimulation und Oxytocinbelastung zur Vorhersage eines fetalen Distress am Termin
Die Akzeleration der fetalen Herzfrequenz nach vibroakustischer Stimulation ist insbesondere nach der 28. Woche ein zuverlässiger Parameter bei der fetalen Zustandsdiagnostik. In den meisten klinischen Studien wurde die Aussagekraft eines akustischen Stimulationstest (AST) im Hinblick auf ein fetales Distress mit dem normalen Non-stress-Test (NST) verglichen. Bei der vorliegenden randomisierten Versuchsreihe, die prospektiv angelegt wurde, wollten wir prüfen 1. wie häufig ein pathologischer AST bei Feten am Termin ist, die auch im NST nicht reagierten, 2. ob ein AST das Ergebnis eines nachfolgenden OBT beeinflußt und 3. die Aussagekraft des AST im Vergleich mit dem OBT im Hinblick auf den fetalen Zustand am Termin. 121 Frauen am Termin (38—42 Schwangerschaftswochen), die einen unkomplizierten Schwangerschaftsver-. lauf hatten und wegen eines routinemäßig durchgeführten non-reaktiven oder verdächtigen NST innerhalb eines Jahres zu uns überwiesen wurden, nahmen an der Studie teil. Die Frauen wurden anhand ihrer Personalausweisnummer 2 Gruppen zufallsmäßig zugeordnet. Gruppe A (n = 62) erhielt einen AST und im Anschluß daran einen OBT. Bei den Frauen der Gruppe B (n = 59) wurde lediglich ein OBT durchgeführt. In der Gruppe A hatten 14 Frauen (22,5%) einen non-reaktiven AST vor dem OBT. Abnorme OBT's traten in der Gruppe A nicht so häufig auf wie in der Gruppe B (9 Fälle = 14,5% vs. 14 Fälle = 23,7%), jedoch war der Unterschied nicht signifikant. Alle 9 Frauen der Gruppe A mit einem patho-
logischen OBT hatten einen non-reaktiven AST vor dem OBT. Tab. 2 zeigt die Häufigkeit eines fetalen Distress unter der Geburt bei den Patientinnen, die einen AST und/oder OBT erhalten hatten sowie die prädikativen Werte dieser beiden Tests im Hinblick auf ein fetales Distress in dem untersuchten Kollektiv. Ein antenataler oder intrapartualer Todesfall trat bei den 121 Patienten nicht auf. Suspekte OBT's waren bei Frauen, die vor dem OBT einen AST hatten, nicht so häufig, jedoch war der Unterschied nicht signifikant. Wir glauben daher nicht, daß der AST die Ergebnisse des OBT bei beeinträchtigten Feten verbessert. Die positiven und negativen prädikativen Werte des AST im Hinblick auf einen auffalligen OBT betrugen 64% bzw. 100%, während die Sensitivität bei 100% und die Spezifität bei 91% lagen. Vergleicht man nun die Aussagekraft des AST allein mit der Aussagekraft des OBT allein bei den Frauen, wo nach Randomisierung AST und OBT durchgeführt wurden, so zeigt sich, daß AST und OBT im Hinblick auf ein fetales Distress eine vergleichbare Spezifität und vergleichbare negative prädiktive Werte haben. Die Sensitivität und der positive prädiktive Wert sind jedoch beim AST besser. Unsere Studie zeigt, daß der AST als zweites Verfahren beim non-teaktiven NST am Termin zur fetalen Zustandsdiagnostik eingesetzt werden kann, da er sich mindestens ebenso gut eignet wie der traditionelle OBT. Darüberhinaus ist der AST einfacher und schneller durchzuführen, speziell bei ambulanten Patientinnen. Schließlich ist er auch billiger.
Schlüsselwörter: Belastungstest durch akustische Stimulation, Oxytocin.
Resume
fiable de bonne sante foetale, tout particulierement apres la 28eme semaine de grossesse. Dans de nombreux essais cliniques realises de la sorte, l'efficacite U acceleration du rythme cardiaque foetal, en reaction d'un test de Stimulation acoustique (TSA) pour predire Brought to you | New York Universityfoetale BobstaLibrary Technical Services la souffrance ete comparee avec le non-stress ä une Stimulation vibro-acoustique, represente unby signe
Test de stimulation acoustique pour prevoir de facon fiable la souffrance fatale, comparaison avec le test a l'ocytocine a terme
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J. Perinat. Med. 20 (1992)
279
Schiff et al, Acoustic stimulation test test standard (NST). Get essai controle randomise et prospectif a ete realise pour essayer de determiner: 1) Pincidence d'un TSA anormal chez les foetus presentant un NST non-reactif ä terme; 2) 1'influence d'un TSA sur le resultat d'un test ä l'ocytocine (TO) ulterieur; 3) la valeur du TSA, en comparaison avec le TO, comme indicateur du bien etre foetal au cours des grossesse a terme. 121 femmes enceintes, ä terme (38—42 semaines), avec une grossesse non compliquee, et qui ont ete admises dans notre centre d'accouchement, sur une periode d'un an, en raison d'un non-stress test de routine non-reactif ou suspect au moment de 1'admission, ont ete incorporees dans cette etude. Ces femmes ont ete divisees, de fagon randomisee, sur la base de leur nombre d'identification de citoyennete, en deux groupes. Les femmes du groupe A (n = 62) ont subi un TSA et ensuite un TO. Les femmes du groupe B (n = 59) n'ont subi qu'un TO. Parmi les femmes du groupe A, 14 (22,5%) presentaient un TSA non-reactif avant le TO. Le taux de TO anormaux etait inferieur, mais pas de fagon significative, chez les patientes du groupe A (9 cas, 14,5%), en comparaison avec celles du groupe B (14 cas, 23,7%). Les neufs cas du groupe A qui presentaient un TO anormal avaient un TSA non-reactif avant le TO. Le tableau 2 presente 1'incidence de la souffrance foetale au cours du travail chez les patientes ay ant benefice d'un TSA et/ou d'un TO, ainsi que la capacite de ces deux tests a predire la souffrance foetale parmi la population etudiee. II n'y a pas eu de cas de mortalite antenatale ni per-partum, chez les 121 patientes.
Bien que le nombre de resultats de TO anormaux soit inferieur chez les femmes ayant eu, avant le TO, un TSA cette difference n'est pas significative et, ainsi, nous concluons que le TSA, en soi, n'ameliore pas les resultats du TO. Les valeurs predictives positives et negatives du TSA pour la prediction d'un TO anormal sont, respectivement de 64% et de 100%, tandis que la sensibilite et la specificite sont respectivement de 100% et de 91%. Si compare les capacites du TSA, en tant que test unique, dans le groupe randomise pour subir les deux tests, TSA et TO, aux capacites du TO, en tant que test unique, dans les deux groupes, pour prevoir la souffrance foetale au cours du travail culterieur, nous trouvons que le TSA a une specificite et une valeur predictive negratives similaire ä celles du TO, mais une sensibilite et une valeur predictive quelque peu augmentees. Get essai demontre que le TSA peut jouer le role d'examen de seconde intention pour revaluation du bien etre foetal lorsque le NST n'est pas reactif, ä terme, avec en prime de meilleures capacites diagnostiques que le traditionnel TO. En outre, en comparaison avec le TO, le TSA est plus aise, plus rapide et vraissemblablement moins eher ä realiser, etb cela tout particulierement chez les patientes en ambulatoire. Aussi suggerons nous que, dans ces cas, le TSA puisse remplacer le TO, ou du moins limiter les indications du TO uniquement aux cas avec un TSA non-reactif, apres un NST anterieur non-reactif.
Mots-cles: Ocytocine, test de stimulation acoustique.
References
[7] SMITH CV, JP PHELAN, RH PAUL et al: Fetal [1] BIRNHOLTZ JC, BR BENACERRAF: The developacoustic stimulation testing: A retrospective exment of human fetal hearing. Science 222 (1983) perience with the fetal acoustic stimulation test. 516 Am J Obstet Gynecol 153 (1985) 567 [2] INGEMARSSON I, S ARULKUMARAN: Reactive fetal [8] SMITH CV, JP PHELAN, LD PLATT et al: Fetal heart rate response to vibroacoustic stimulation acoustic stimulation testing. II. A randomized cliin fetuses with low scalp blood pH. Br J Obstet nical comparison with the nonstress test. Am J Gynecol 96 (1989) 562 [3] PEIPER A: Sinnesempfindungen des Kindes vor Obstet Gynecol 155 (1986) 131 [9] WESTGREN M, H ALMSTROM, M NYMAN, U ULMseiner Geburt. Monatsschr Kinderheilkad 29 STEM: Maternal perception of sound-provoked fe(1925) 236 [4] POLZIN GB, KJ BLAKEMORE, RH PETREE, E AMON: tal movements as a measure of fetal well-being. Fetal vibro-acoustic stimulation: Magnitude and Br J Obstet Gynecol 94 (1987) 523 duration of fetal heart rate accelerations as a marker of fetal health. Obstet Gynecol 72 (1988) Received July 14, 1991. Revised January 24, 1992. 621 Accepted February 4, 1992. [5] READ JA, FC MILLER: Fetal heart rate acceleration in response to acoustic stimulation as a meaEyal Schiff, M. D. sure of fetal well-being. Am J Obstet Gynecol 129 Dept. Obstet. & Gynecol. (1977) 512 Sheba Medical Center [6] ROMERO R, M MAZOR, JC HOBBINS: A critical Tel-Hashomer 52621 appraisal of fetal acoustic stimulation as an anIsrael tenatal test for fetal well-being. Obstet Gynecol 71 (1988) 781 Brought to you by | New York University Bobst Library Technical Services J. Perinat. Med. 20 (1992)
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