A description of externally recorded womb sounds in human subjects during gestation

Abstract

ObjectiveReducing environmental noise benefits premature infants in neonatal intensive care units (NICU), but excessive reduction may lead to sensory deprivation, compromising development. Instead of minimal noise levels, environments that mimic intrauterine soundscapes may facilitate infant development by providing a sound environment reflecting fetal life. This soundscape may support autonomic and emotional development in preterm infants. We aimed to assess the efficacy and feasibility of external non-invasive recordings in pregnant women, endeavoring to capture intra-abdominal or womb sounds during pregnancy with electronic stethoscopes and build a womb sound library to assess sound trends with gestational development. We also compared these sounds to popular commercial womb sounds marketed to new parents.Study designIntra-abdominal sounds from 50 mothers in their second and third trimester (13 to 40 weeks) of pregnancy were recorded for 6 minutes in a quiet clinic room with 4 electronic stethoscopes, placed in the right upper and lower quadrants, and left upper and lower quadrants of the abdomen. These recording were partitioned into 2-minute intervals in three different positions: standing, sitting and lying supine. Maternal and gestational age, Body Mass Index (BMI) and time since last meal were collected during recordings. Recordings were analyzed using long-term average spectral and waveform analysis, and compared to sounds from non-pregnant abdomens and commercially-marketed womb sounds selected for their availability, popularity, and claims they mimic the intrauterine environment.ResultsMaternal sounds shared certain common characteristics, but varied with gestational age. With fetal development, the maternal abdomen filtered high (500–5,000 Hz) and mid-frequency (100–500 Hz) energy bands, but no change appeared in contributions from low-frequency signals (10–100 Hz) with gestational age. Variation appeared between mothers, suggesting a resonant chamber role for intra-abdominal space. Compared to commercially-marketed sounds, womb signals were dominated by bowel sounds, were of lower frequency, and showed more variation in intensity.ConclusionsHigh-fidelity intra-abdominal or womb sounds during pregnancy can be recorded non-invasively. Recordings vary with gestational age, and show a predominance of low frequency noise and bowel sounds which are distinct from popular commercial products. Such recordings may be utilized to determine whether sounds influence preterm infant development in the NICU.

Neural encoding of voice pitch and formant structure at birth as revealed by frequency-following responses

“…But, what speech sound features do babies rely upon to exhibit such identification skills? Considering that the mother’s womb acts as a low-pass filter, the sounds available to a fetus during the gestation period are dominated by a low frequency content (< 500 Hz 5 , 67 – 69 ), while higher frequency ranges, which characterize most of the temporal fine structure of speech 46 , 70 , would only be fully available at birth. Indeed, neonates may base their preferences on pitch contours and slow temporal dynamics, features available during pregnancy 71 – 73 .…”

Prenatal daily musical exposure is associated with enhanced neural representation of speech fundamental frequency: Evidence from neonatal frequency‐following responses

“…It is worth noting that linguistic prosody and non‐vocal musical patterns are readily available to fetuses due to the low‐pass filter characteristics of the mother's womb (Gerhardt & Abrams, 2000; Jeng, 2017; McCarthy et al., 2019; Parga et al., 2018). These characteristics may explain why healthy newborns exhibit an adult‐like neural encoding of speech F 0 , while the encoding of other speech features, based on sound frequencies higher than the womb's low‐pass cutoff, are still undeveloped (Arenillas‐Alcón et al., 2021a).…”

“…The accurate encoding and tracking of F 0 play an essential role in the future acquisition of language and sound processing, including the perception of melodies, harmony in music or prosody in speech, as well as language comprehension in noisy environments, perception of the emotional content of a conversation, phoneme acquisition in tonal languages, recognition of speakers or speech segmentation, among others (Arenillas‐Alcón et al., 2021a; Benavides‐Varela et al., 2012; Cabrera & Gervain, 2020; Gervain, 2018; Musacchia et al., 2007; Partanen et al., 2013; Plack et al., 2014; Ribas‐Prats et al., 2022). Because the mother's womb acts as a low‐pass filter, only allowing the transmission of sound frequencies below 500 Hz (Gerhardt & Abrams, 2000; Jeng, 2017; McCarthy et al., 2019; Parga et al., 2018), sounds available to the fetus are mainly dominated by these frequency ranges. The consequences of this prenatal exposure to low‐frequencies, which are typical of human speech (from 100–255 Hz (Traunmüller & Eriksson, 1995)), support the idea of an increased sensitivity of the auditory system regarding low‐frequency ranges and may offer an explanation to the remarkable adult‐like status observed already at birth in the encoding of F 0 (Arenillas‐Alcón et al., 2021a).…”

Foetal Music Perception: A Comparison Study between Heart Rate and Motor Responses Assessed by APIB Scale in Ultrasound Exam

“…The external sound source, both the voice singing and the musical instrument, was at a distance of 100cm from the mother's abdomen and was issued at an average intensity of 80dB (±20). Considering the level of noise in the womb may range from 70 to 90dB and external noise (average intensity of both expected internal-womb and external noise), the external sound stimuli were issued at an intensity of noise level that would offset at least 10 to 40 dB of overall noise level [31].…”