Gélat, P;
David, AL;
Haqhenas, SR;
Henriques, J;
Thibaut de Maisieres, A;
White, T;
Jauniaux, E;
(2019)
Evaluation of fetal exposure to external loud noise using a sheep model: Quantification of in-utero acoustic transmission across the human audio range.
American Journal of Obstetrics and Gynecology
10.1016/j.ajog.2019.05.036.
(In press).
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Abstract
BACKGROUND: There is mounting evidence that neural memory traces are formed by auditory learning in-utero and that premature newborns are particularly sensitive to the intense, sustained noises or impulses sounds associated with the use of intensive care equipment. One area of critical importance is the determination of sound level exposure in-utero associated with maternal occupation. The attenuation factors provided by the abdomen and tissue as well as the routes by which the inner ear receives stimulation need careful consideration and investigation to provide prenatal protection from external sound levels and frequencies at which harm may be caused. OBJECTIVE: To measure how sound from external sound sources is transmitted inside the womb on a fetal sheep model in 6 Hz frequency steps between 100 Hz and 20 kHz, i.e. across most of the human audio range. STUDY DESIGN: We measured acoustic transfer characteristics in-vivo in six time-mated singleton pregnant Romney ewes (gestational age 103-130 days, weight 54-74 kg). Under general anaesthesia and at hysterotomy, a calibrated hydrophone was attached to the occiput of the fetal head within the amniotic sac. Two calibrated microphones were positioned in the operating theatre, close to the head and to the body of each ewe. Initial experiments were carried out on three pregnant ewes three days after transport recovery, to inform the data acquisition protocol. This was followed by detailed data acquisition of three pregnant ewes under general anaesthesia, using external white noise signals. Voltage signals were acquired with two calibrated microphones, located near the head and the body of each ewe and with a calibrated hydrophone located in the amniotic fluid. RESULTS: Measurement of acoustic transmission through the maternal abdominal and uterine walls indicates that frequency contents above 10 kHz are transmitted into the amniotic sac, and that some frequencies are attenuated by as little as 3 dB. CONCLUSION: This study provides new data about in-utero sound transmission of external noise sources, beyond physiological noise (cardiovascular, respiratory, and intestinal sounds) which help quantity the potential for fetal physiological damage resulting from exposure to high levels of noise during pregnancy. Fine frequency acoustic attenuation characteristics are essential to inform standards and clinical recommendations on exposure of pregnant women to noise. Such transfer functions may also inform the design of filters to produce an optimal acoustic setting for maternal occupational noise exposure, use of magnetic resonance imaging during pregnancy and for neonatal incubators.
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