AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 4
October 1990
INTRAUTERINE SOUND LEVELS: INTRAPARTUM ASSESSMENT WITH AN INTRAUTERINE MICROPHONE Carl V Smith, M.D., Brian Satt, Ph.D., Jeffrey P. Phelan, M.D., and Richard H. Paul, M.D.
The complex mechanisms responsible for fetal hearing are in place and functional by 26 weeks of gestation, but little is known about the acoustic milieu of the amniotic cavity. We placed an electrically isolated microphone in the uterus of nine term gravid volunteers after amniorrhexis. Baseline levels of intrauterine sound were 72 to 88 db. Transabdominal vibroacoustic stimulation with an artificial larynx produced peak mixed frequency sound Ievelsof91 to 111 db. We conclude that the term fetus in labor is exposed to physiologic sound levels higher than we had anticipated; the application of a quantifiable sound stimulus to the maternal abdominal wall results in a small increment in intrauterine sound; and within the limits specified, experimental fetal acoustic stimulation should pose no major risks.
Fetal neural and cochlear development are thought to be nearly complete by the 25th week of pregnancy.1 Thus, the fundamental mechanisms are in place to support fetal hearing. This was substantiated as early as 1925 when Pieper reported fetal movement in response to acoustic stimulation.2 Others have confirmed his findings.34 In the early 1970s, in an attempt to define the levels of sound present within the amniotic cavity, intrauterine microphones were placed and sound pressure levels ranging between 84 and 96 db were observed.5-6 In addition to the measurement of sound levels other investigators began using acoustic stimulation to evoke fetal movement or acceleration of the fetal heart rate (FHR) in an attempt to assess fetal wellbeing.7-9 Recent reports from our institution have demonstrated the apparent effectiveness of vibroacoustic stimulation of the fetus in reducing the number of nonreactive tests.1011 The purpose of the current investigation was to evaluate the level of background sound within the amniotic cavity and to determine the sound transmission characteristics of externally applied sound through the maternal abdominal and uterine walls.
MATERIALS AND METHODS
Patients presenting in early labor or after spontaneous rupture of the membranes at term were considered candidates for this investigation. Inclusion criteria were a term pregnancy, ruptured membranes, cervical dilation of at least 3 cm, an engaged cephalic presenting part, and a reactive FHR pattern and no known in utero exposure to any drugs or chemicals. Exclusion criteria included a history of prior cesarean delivery, abnormal FHR pattern, noncephalic presentation, and thick meconiumstained amniotic fluid. This investigation was approved by the institutional review board and Human Research Committee. After obtaining informed consent, a vaginal examination to confirm the presentation and station was performed. Subsequently, the intrauterine microphone was introduced transcervically and directed to a position adjacent to the anterior fetal ear. Real-time ultrasound was then performed to confirm the location of the microphone. Although placental location was not an exclusion criteria, in no case was there placenta located between the micro-
Department of Obstetrics and Gynecology University of Southern California School of Medicine and Women's Hospital, Los Angeles County/USC Medical Center, Los Angeles, California The opinions or assertions contained herein are those of the authors and are not to be construed as official or those representing the United States Navy or Department of Defense Reprint requests: Dr. Smith, Department of Obstetrics and Gynecology, The University of Nebraska Medical Center, 42nd and Dewey Avenue, Omaha, NE 68105
312
Copyright © 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: East Carolina University. Copyrighted material.
ABSTRACT
INTRAUTERINE SOUND LEVELS/Smith, Satt, Phelan, et al.
to be 90 db and calibrated by the Realistic Sound Level Meter. Since the cushion was placed on the maternal abdomen, it was thought that this measurement at the speaker face would accurately reflect the sound level at the surface of the maternal abdomen. Peak intrauterine levels were then determined. RESULTS
Nine patients participated in this investigation. No adverse fetal or maternal outcomes were encountered as a direct result of the intrauterine microphone placement. Table 1 lists the sound pressure levels within the uterus peak levels following stimulation with the EAL, and the arithmetic difference. Baseline levels of intrauterine sound ranged between 72 and 88 db. During periods of vibroacoustic stimulation, increases of 5 to 38 db were noted. Table 2 displays the increase in sound levels across the abdominal and uterine walls using pure tone stimuli. Consistent increases in the measured levels were observed until a frequency of greater than 2000 hz was reached. In all nine patients fetal movement and fetal heart rate accelerations were present during simulation with the EAL. Fetal movement occurred variably with pure tone stimuli and was not observed with frequencies greater than 2000 Hz.
Downloaded by: East Carolina University. Copyrighted material.
phone and the maternal abdominal wall. Maternal obesity was also not a contraindication to inclusion in the study, but in no case did the distance between the maternal abdominal wall and the microphone exceed 5 cm. The microphone was an electret type sold by Radio Shack (Model 42-3019). It was selected for use because of its small dimension (10 mm diameter), frequency response, and sensitivity. The unit was sealed inside a contoured acrylic hosing that was, in turn, placed at the end of a 5 mm semiflexible plastic tube. This tube served as a conduit for the electrical connections as well as an introducer. The frequency response of the system covered a range of 10 hz to 10 kHz (+4 db). The sensitivity was rated at —65 db and was found to be adequate for this investigation. The unit was then carefully sealed with silicone rubber to prevent fluid leakage. The microphone and its housing was covered with a latex sheath and an elastic band. The entire assembly was then sterilized with ethylene oxide. In addition the microphone was calibrated against a Bruel and Kjaer (model 2230) sound-level meter over a range of 50 Hz to 5 kHz. The experimental microphone probe was within +4 db of the standard over the frequency range of interest (50 to 2000 Hz). After insertion, the microphone was connected to a battery-operated realistic sound-level meter (model 40-3019) and a battery-operated cassette recorder. Sound-level measurements were made in C-weighting. Transabdominal acoustic stimulation was then accomplished with a model 5C electronic artificial larynx (EAL). Previously performed spectral analysis of the output of the EAL revealed a fundamental frequency of 80 Hz with the presence of subharmonics ranging from 20 to 9000 Hz.10 The EAL was placed lightly on the maternal abdomen, overlying the microphone and fetal ear. Since the force applied to the device could potentially affect sound transmission characteristics, the same investigator (C. VS.) applied the EAL to each of the subjects. In addition, a coupling gel was not used. Peak intrauterine sound pressure levels were then recorded. Three successive stimulus trials were performed and the maximum sound pressure level was recorded. The sound transmission characteristics of pure tone stimuli were ascertained. A cushioned 5 inch speaker was placed overlying the intrauterine microphone. The pure tones were generated by a modified Health kit amplifier (Model AA-18) in four patients. Tones were produced by a sine-wave generator and recorded on cassettes in the remaining five patients. This recorder was then connected to the speaker just described. The duration of the stimulus was variable because it was continued until the sound pressure level reached a stable level that was measurably different from the prestimulus values. In no case did the duration of the stimulus exceed 1 minute. All experiments were carried out in a quiet, but not sound-proofed, labor room. The sound pressure at the surface of the speaker was arbitrarily chosen
DISCUSSION
The ability of the human fetus to hear has been demonstrated for many years. Similarly, the presence of background noise within the uterus has been accepted but poorly understood. These levels have reported to be as high as 95 db.5 Walker and colleagues5 and Henshall6 placed intrauterine microphones in 1971 and 1972 to explore the aquatic environment of the fetus. The reported levels were similar to the ones reported by the present investigation. The most likely explanation for this magnitude of sound level is the contribution of maternal vascu-
Table 1. Intrauterine Sound Levels: Baseline and During Vibroacoustic Stimulation Patient
No. 1 2 3 4 5 6 7 8 9
Baseline (db)
During Vibroacoustic Stimulation (db)
Change
82 78 73 88 83 72 84 87 84
110 98 111 106 98 91 107 92 101
28 20 38 18 15 19 23 5 17
313
Table 2.
Pure-Tone Stimulation Change in Frequency Sound Level (hz) (db)
Modified health kit amplifier
Sine-wave generator
500 850 1000 2000 3000 50 100 500 750 1000 2000
7.25 3.75 2.0 0 0 4.6 5.2 9.6 11.2 3.0 1.6
lar noise to the intrauterine environment. The peak levels reported by Walker and colleagues5 were coincident with the maternal R wave on a simultaneously recorded electrocardiograph (ECG). Although ECGs were not recorded in the present study, we observed peak levels during maternal systole. In fact, subjectively the most obvious component of the intrauterine sound was maternal pulse. The precise vascular structure from which these sounds emanate remains speculative. Higher levels of sound were recorded during periods of transabdominal acoustic stimulation. Since the output of the EAL averaged 84 db at 1 meter in air, the levels observed were 7 to 26 db higher with the uterus. This might appear to represent "passive amplification" of sound through the maternal abdominal and uterine walls. However, these levels represent enhanced sound transmission because the EAL is mechanically coupled to the maternal skin and the microphone was placed in a medium with enhanced sound transmission characteristics. This same phenomenon was observed in the laboratory by the 22 db increase in sound levels with the addition of water to the container. The enhanced transmission of sound in water is a well-known fact. Of vital importance is the safety of the 110 db recorded during acoustic stimulation. An important point is the duration of exposure, since damage to hearing at this level could occur if exposure were prolonged. However with 1- to 3-second pulses, the likelihood of damage is remote.12 Additionally during audiometry performed in the neonatal period, sound pressure levels at the 100 to 110 db range are utilized with no apparent injury.13 Uncertainty remains as to the overall safety of vibroacoustic stimulation of the human fetus. A recent report by Ohel and colleagues14 reported no abnormalities in neonatal auditory testing in those fetuses who underwent vibracoustic stimulation. Additional studies are needed to address more definitely the issue of safety. Although not performed by us, spectral analysis of intrauterine sound would be of considerable interest. As would be expected, we encountered a bewil314 dering array of sounds. Some, such as maternal
October 1990
bowel and vascular sounds, were easily identified. Other higher frequency sounds were occasionally heard. Spectral analysis of these sounds, particularly if combined with real-time ultrasonography of the fetus, may allow investigators to understand better the fetal environment. Finally, analysis of sound during acoustic stimulation may allow identification of the precise component of the output of the EAL that elicits the consistent responses that have been reported. 1011 Spectral analysis would have also been of value in explaining the results noted in Table 2. Clearly, attenuation across the abdominal wall is present and more prominent at higher frequencies. Marked attenuation was evident beginning at 1000 Hz so that at 2000 Hz or greater no measurable increase in sound levels were observed. An interesting observation, however, was that above 2000 Hz we could "hear" the tone on the recording despite not being able to measure the sound level. The present study confirms that the fetus is by no means deprived of sensory stimulation. Indeed, the amniotic cavity is quite noisy. The sounds are derived from maternal sources and from external sources as well. In addition to the EAL, pure tonal stimuli are audible and human speech was both audible and understandable. These observations lead to interesting speculation regarding the intrauterine environment and the way in which altering it could modify fetal behavior. In summary, baseline levels of intrauterine sound up to 88 db were observed. Acoustic stimulation, which increased these levels, was not associated with an unsafe sound pressure level. The clarity of the intrauterine recording and the previously reported demonstrated fetal response to sound suggest that additional investigation regarding sound and its transmission characteristics should be undertaken.
REFERENCES 1. Johanson B, Wedenberg E, Westin B: Measurement of the response by the human foetus. Acta Otolaryngol (Stockh) 57:188, 1964 2. Peiper A: Sinnesempfindungen der Kindes vor seiner Geburt. Monatsschr Kinderheilk 29:236, 1927 3. Dwornicka B, Jasienka A, Smolarz W, et al: Attempt of determining the fetal reaction to acoustic stimulation. Acta Otolaryngol (Stockh) 57:571, 1963 4. Tanaka Y, Aryama T: Fetal responses to acoustic stimuli. Pract Otorhinolaryngol 31:269, 1969 5. Walker D, Grimwade J, Wood C: Intrauterine noise: A component of the fetal environment. Am J Obstet Gynecol 109:91, 1971 6. Henshall WR: Intrauterine sound levels. Am J Obstet Gynecol 112:576, 1972 7. Read JA, Miller FC; Fetal heart rate acceleration in response to acoustic stimulation as a measure of fetal well-being. AmJ Obstet Gynecol 129:512, 1977 8. Jensen OH: Fetal heart rate response to controlled sound stimuli during the third trimester of normal pregnancy. Acta Obstet Gynecol Scand 63:193, 1984 9. Serafini P, Lindsay MB, Nagey DA, et al: Antepartum fetal heart rate response to sound stimulation: The acoustic stimulation test. AmJ Obstet Gynecol 148:41, 1984
Downloaded by: East Carolina University. Copyrighted material.
AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 4
INTRAUTERINE SOUND LEVELS/Smith, Satt, Phelan, et al.
10. Smith CV, Phelan JP, Platt LD, et al: Fetal acoustic stimulation testing. A retrospective experience with the fetal acoustic stimulation test. Am J Obstet Gynecol 153:567, 1985 11. Smith CV, Phelan JP, Platt LD, et al: Fetal acoustic stimulation testing II. A randomized clinical comparison with the nonstress test. Am J Obstet Gynecol 155:131, 1986 12. Burns W, Robinson DW: An investigation of the effects of occupational noise on hearing. In Wolstenholme GEW,
tion Symposium. London: JEA Churchill 1970, pp 171-192 13. Wedenberg E: Auditory tests on newborn infants. In Cunningham, G (ed): Conference on Newborn Hearing Screen-
ing, Washington, DC: A.G. Bell Association, 1972, pp 410-425 14. Ohel G, Horowitz E, Linder N, Sohmer H: Neonatal auditory acuity following in utero vibroacoustic stimulation. Am J Obstet Gynecol 157:440, 1987
Downloaded by: East Carolina University. Copyrighted material.
Knight F (eds): Sensorineural Hearing Loss. Ciba Founda-
315
October 1990
INTRAUTERINE SOUND LEVELS: INTRAPARTUM ASSESSMENT WITH AN INTRAUTERINE MICROPHONE Carl V Smith, M.D., Brian Satt, Ph.D., Jeffrey P. Phelan, M.D., and Richard H. Paul, M.D.
The complex mechanisms responsible for fetal hearing are in place and functional by 26 weeks of gestation, but little is known about the acoustic milieu of the amniotic cavity. We placed an electrically isolated microphone in the uterus of nine term gravid volunteers after amniorrhexis. Baseline levels of intrauterine sound were 72 to 88 db. Transabdominal vibroacoustic stimulation with an artificial larynx produced peak mixed frequency sound Ievelsof91 to 111 db. We conclude that the term fetus in labor is exposed to physiologic sound levels higher than we had anticipated; the application of a quantifiable sound stimulus to the maternal abdominal wall results in a small increment in intrauterine sound; and within the limits specified, experimental fetal acoustic stimulation should pose no major risks.
Fetal neural and cochlear development are thought to be nearly complete by the 25th week of pregnancy.1 Thus, the fundamental mechanisms are in place to support fetal hearing. This was substantiated as early as 1925 when Pieper reported fetal movement in response to acoustic stimulation.2 Others have confirmed his findings.34 In the early 1970s, in an attempt to define the levels of sound present within the amniotic cavity, intrauterine microphones were placed and sound pressure levels ranging between 84 and 96 db were observed.5-6 In addition to the measurement of sound levels other investigators began using acoustic stimulation to evoke fetal movement or acceleration of the fetal heart rate (FHR) in an attempt to assess fetal wellbeing.7-9 Recent reports from our institution have demonstrated the apparent effectiveness of vibroacoustic stimulation of the fetus in reducing the number of nonreactive tests.1011 The purpose of the current investigation was to evaluate the level of background sound within the amniotic cavity and to determine the sound transmission characteristics of externally applied sound through the maternal abdominal and uterine walls.
MATERIALS AND METHODS
Patients presenting in early labor or after spontaneous rupture of the membranes at term were considered candidates for this investigation. Inclusion criteria were a term pregnancy, ruptured membranes, cervical dilation of at least 3 cm, an engaged cephalic presenting part, and a reactive FHR pattern and no known in utero exposure to any drugs or chemicals. Exclusion criteria included a history of prior cesarean delivery, abnormal FHR pattern, noncephalic presentation, and thick meconiumstained amniotic fluid. This investigation was approved by the institutional review board and Human Research Committee. After obtaining informed consent, a vaginal examination to confirm the presentation and station was performed. Subsequently, the intrauterine microphone was introduced transcervically and directed to a position adjacent to the anterior fetal ear. Real-time ultrasound was then performed to confirm the location of the microphone. Although placental location was not an exclusion criteria, in no case was there placenta located between the micro-
Department of Obstetrics and Gynecology University of Southern California School of Medicine and Women's Hospital, Los Angeles County/USC Medical Center, Los Angeles, California The opinions or assertions contained herein are those of the authors and are not to be construed as official or those representing the United States Navy or Department of Defense Reprint requests: Dr. Smith, Department of Obstetrics and Gynecology, The University of Nebraska Medical Center, 42nd and Dewey Avenue, Omaha, NE 68105
312
Copyright © 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
Downloaded by: East Carolina University. Copyrighted material.
ABSTRACT
INTRAUTERINE SOUND LEVELS/Smith, Satt, Phelan, et al.
to be 90 db and calibrated by the Realistic Sound Level Meter. Since the cushion was placed on the maternal abdomen, it was thought that this measurement at the speaker face would accurately reflect the sound level at the surface of the maternal abdomen. Peak intrauterine levels were then determined. RESULTS
Nine patients participated in this investigation. No adverse fetal or maternal outcomes were encountered as a direct result of the intrauterine microphone placement. Table 1 lists the sound pressure levels within the uterus peak levels following stimulation with the EAL, and the arithmetic difference. Baseline levels of intrauterine sound ranged between 72 and 88 db. During periods of vibroacoustic stimulation, increases of 5 to 38 db were noted. Table 2 displays the increase in sound levels across the abdominal and uterine walls using pure tone stimuli. Consistent increases in the measured levels were observed until a frequency of greater than 2000 hz was reached. In all nine patients fetal movement and fetal heart rate accelerations were present during simulation with the EAL. Fetal movement occurred variably with pure tone stimuli and was not observed with frequencies greater than 2000 Hz.
Downloaded by: East Carolina University. Copyrighted material.
phone and the maternal abdominal wall. Maternal obesity was also not a contraindication to inclusion in the study, but in no case did the distance between the maternal abdominal wall and the microphone exceed 5 cm. The microphone was an electret type sold by Radio Shack (Model 42-3019). It was selected for use because of its small dimension (10 mm diameter), frequency response, and sensitivity. The unit was sealed inside a contoured acrylic hosing that was, in turn, placed at the end of a 5 mm semiflexible plastic tube. This tube served as a conduit for the electrical connections as well as an introducer. The frequency response of the system covered a range of 10 hz to 10 kHz (+4 db). The sensitivity was rated at —65 db and was found to be adequate for this investigation. The unit was then carefully sealed with silicone rubber to prevent fluid leakage. The microphone and its housing was covered with a latex sheath and an elastic band. The entire assembly was then sterilized with ethylene oxide. In addition the microphone was calibrated against a Bruel and Kjaer (model 2230) sound-level meter over a range of 50 Hz to 5 kHz. The experimental microphone probe was within +4 db of the standard over the frequency range of interest (50 to 2000 Hz). After insertion, the microphone was connected to a battery-operated realistic sound-level meter (model 40-3019) and a battery-operated cassette recorder. Sound-level measurements were made in C-weighting. Transabdominal acoustic stimulation was then accomplished with a model 5C electronic artificial larynx (EAL). Previously performed spectral analysis of the output of the EAL revealed a fundamental frequency of 80 Hz with the presence of subharmonics ranging from 20 to 9000 Hz.10 The EAL was placed lightly on the maternal abdomen, overlying the microphone and fetal ear. Since the force applied to the device could potentially affect sound transmission characteristics, the same investigator (C. VS.) applied the EAL to each of the subjects. In addition, a coupling gel was not used. Peak intrauterine sound pressure levels were then recorded. Three successive stimulus trials were performed and the maximum sound pressure level was recorded. The sound transmission characteristics of pure tone stimuli were ascertained. A cushioned 5 inch speaker was placed overlying the intrauterine microphone. The pure tones were generated by a modified Health kit amplifier (Model AA-18) in four patients. Tones were produced by a sine-wave generator and recorded on cassettes in the remaining five patients. This recorder was then connected to the speaker just described. The duration of the stimulus was variable because it was continued until the sound pressure level reached a stable level that was measurably different from the prestimulus values. In no case did the duration of the stimulus exceed 1 minute. All experiments were carried out in a quiet, but not sound-proofed, labor room. The sound pressure at the surface of the speaker was arbitrarily chosen
DISCUSSION
The ability of the human fetus to hear has been demonstrated for many years. Similarly, the presence of background noise within the uterus has been accepted but poorly understood. These levels have reported to be as high as 95 db.5 Walker and colleagues5 and Henshall6 placed intrauterine microphones in 1971 and 1972 to explore the aquatic environment of the fetus. The reported levels were similar to the ones reported by the present investigation. The most likely explanation for this magnitude of sound level is the contribution of maternal vascu-
Table 1. Intrauterine Sound Levels: Baseline and During Vibroacoustic Stimulation Patient
No. 1 2 3 4 5 6 7 8 9
Baseline (db)
During Vibroacoustic Stimulation (db)
Change
82 78 73 88 83 72 84 87 84
110 98 111 106 98 91 107 92 101
28 20 38 18 15 19 23 5 17
313
Table 2.
Pure-Tone Stimulation Change in Frequency Sound Level (hz) (db)
Modified health kit amplifier
Sine-wave generator
500 850 1000 2000 3000 50 100 500 750 1000 2000
7.25 3.75 2.0 0 0 4.6 5.2 9.6 11.2 3.0 1.6
lar noise to the intrauterine environment. The peak levels reported by Walker and colleagues5 were coincident with the maternal R wave on a simultaneously recorded electrocardiograph (ECG). Although ECGs were not recorded in the present study, we observed peak levels during maternal systole. In fact, subjectively the most obvious component of the intrauterine sound was maternal pulse. The precise vascular structure from which these sounds emanate remains speculative. Higher levels of sound were recorded during periods of transabdominal acoustic stimulation. Since the output of the EAL averaged 84 db at 1 meter in air, the levels observed were 7 to 26 db higher with the uterus. This might appear to represent "passive amplification" of sound through the maternal abdominal and uterine walls. However, these levels represent enhanced sound transmission because the EAL is mechanically coupled to the maternal skin and the microphone was placed in a medium with enhanced sound transmission characteristics. This same phenomenon was observed in the laboratory by the 22 db increase in sound levels with the addition of water to the container. The enhanced transmission of sound in water is a well-known fact. Of vital importance is the safety of the 110 db recorded during acoustic stimulation. An important point is the duration of exposure, since damage to hearing at this level could occur if exposure were prolonged. However with 1- to 3-second pulses, the likelihood of damage is remote.12 Additionally during audiometry performed in the neonatal period, sound pressure levels at the 100 to 110 db range are utilized with no apparent injury.13 Uncertainty remains as to the overall safety of vibroacoustic stimulation of the human fetus. A recent report by Ohel and colleagues14 reported no abnormalities in neonatal auditory testing in those fetuses who underwent vibracoustic stimulation. Additional studies are needed to address more definitely the issue of safety. Although not performed by us, spectral analysis of intrauterine sound would be of considerable interest. As would be expected, we encountered a bewil314 dering array of sounds. Some, such as maternal
October 1990
bowel and vascular sounds, were easily identified. Other higher frequency sounds were occasionally heard. Spectral analysis of these sounds, particularly if combined with real-time ultrasonography of the fetus, may allow investigators to understand better the fetal environment. Finally, analysis of sound during acoustic stimulation may allow identification of the precise component of the output of the EAL that elicits the consistent responses that have been reported. 1011 Spectral analysis would have also been of value in explaining the results noted in Table 2. Clearly, attenuation across the abdominal wall is present and more prominent at higher frequencies. Marked attenuation was evident beginning at 1000 Hz so that at 2000 Hz or greater no measurable increase in sound levels were observed. An interesting observation, however, was that above 2000 Hz we could "hear" the tone on the recording despite not being able to measure the sound level. The present study confirms that the fetus is by no means deprived of sensory stimulation. Indeed, the amniotic cavity is quite noisy. The sounds are derived from maternal sources and from external sources as well. In addition to the EAL, pure tonal stimuli are audible and human speech was both audible and understandable. These observations lead to interesting speculation regarding the intrauterine environment and the way in which altering it could modify fetal behavior. In summary, baseline levels of intrauterine sound up to 88 db were observed. Acoustic stimulation, which increased these levels, was not associated with an unsafe sound pressure level. The clarity of the intrauterine recording and the previously reported demonstrated fetal response to sound suggest that additional investigation regarding sound and its transmission characteristics should be undertaken.
REFERENCES 1. Johanson B, Wedenberg E, Westin B: Measurement of the response by the human foetus. Acta Otolaryngol (Stockh) 57:188, 1964 2. Peiper A: Sinnesempfindungen der Kindes vor seiner Geburt. Monatsschr Kinderheilk 29:236, 1927 3. Dwornicka B, Jasienka A, Smolarz W, et al: Attempt of determining the fetal reaction to acoustic stimulation. Acta Otolaryngol (Stockh) 57:571, 1963 4. Tanaka Y, Aryama T: Fetal responses to acoustic stimuli. Pract Otorhinolaryngol 31:269, 1969 5. Walker D, Grimwade J, Wood C: Intrauterine noise: A component of the fetal environment. Am J Obstet Gynecol 109:91, 1971 6. Henshall WR: Intrauterine sound levels. Am J Obstet Gynecol 112:576, 1972 7. Read JA, Miller FC; Fetal heart rate acceleration in response to acoustic stimulation as a measure of fetal well-being. AmJ Obstet Gynecol 129:512, 1977 8. Jensen OH: Fetal heart rate response to controlled sound stimuli during the third trimester of normal pregnancy. Acta Obstet Gynecol Scand 63:193, 1984 9. Serafini P, Lindsay MB, Nagey DA, et al: Antepartum fetal heart rate response to sound stimulation: The acoustic stimulation test. AmJ Obstet Gynecol 148:41, 1984
Downloaded by: East Carolina University. Copyrighted material.
AMERICAN JOURNAL OF PERINATOLOGY/VOLUME 7, NUMBER 4
INTRAUTERINE SOUND LEVELS/Smith, Satt, Phelan, et al.
10. Smith CV, Phelan JP, Platt LD, et al: Fetal acoustic stimulation testing. A retrospective experience with the fetal acoustic stimulation test. Am J Obstet Gynecol 153:567, 1985 11. Smith CV, Phelan JP, Platt LD, et al: Fetal acoustic stimulation testing II. A randomized clinical comparison with the nonstress test. Am J Obstet Gynecol 155:131, 1986 12. Burns W, Robinson DW: An investigation of the effects of occupational noise on hearing. In Wolstenholme GEW,
tion Symposium. London: JEA Churchill 1970, pp 171-192 13. Wedenberg E: Auditory tests on newborn infants. In Cunningham, G (ed): Conference on Newborn Hearing Screen-
ing, Washington, DC: A.G. Bell Association, 1972, pp 410-425 14. Ohel G, Horowitz E, Linder N, Sohmer H: Neonatal auditory acuity following in utero vibroacoustic stimulation. Am J Obstet Gynecol 157:440, 1987
Downloaded by: East Carolina University. Copyrighted material.
Knight F (eds): Sensorineural Hearing Loss. Ciba Founda-
315
