Respuesta fetal a elementos musicales de la voz materna

Abstract

The fetal response to the maternal voice and different external auditory stimuli has been a fascinating field of study over the years. Through different studies, we currently know that fetuses can perceive the mother's voice as early as 16 weeks of gestation. However, the specific perception of the different musical elements in the mother's voice by the fetus, such as timbre, tempo, or pitch, remains to be elucidated. This doctoral thesis aims to design a methodology for intravaginal fetal musical stimulation based on the maternal voice, establish a quantitative procedure to assess the fetal response by 4D ultrasound and analyze the fetal motor response to musical stimulation based on the maternal voice. To investigate this, a study was conducted involving 15 pregnant women in the second trimester. Each participant provided a recording of their voice made, from which 110 different musical stimuli were created by altering the different prosodic characteristics of the maternal voice. These stimuli were categorized according to the organization of sound (habituation, reference, order, and chaos), the speed of reproduction (slow, normal and fast) and the prosodic characteristics (melody, harmony, dynamics, and timbre). Subsequently, fetal musical stimulation was performed. Using an intravaginal playback device to deliver the sound stimuli. Fetal responses were monitored using 4D ultrasound capturing movements or facial expressions. These responses were quantified in a table with a scoring system ranging from 0 (no movement) to 3 (maximum movement). The analysis was carried out by three different observers to assess interobserver agreement and ensure the experiment's reproducibility. To study the association between the different musical stimuli and fetal movements, mixed ordinal regression models adjusted by Bayesian inference were used. To analyze the interobserver agreement, two complementary analyses were conducted: the first to compare pairwise differences between the three observers and the second to characterize the differences in interobserver agreement across the different movement variables. The results of interobserver agreement analysis showed low variability in movements such as tongue protrusion, swallowing, crying, sucking, smiling, yawning, frowning, blinking, finger movement, mouth opening, and grimacing. In contrast, greater variability and more significant differences were observed in the movements of the arms, hands, legs, and head. Regarding the fetal response to the different musical stimuli, the variables "“chaos” and “fast speed” most frequently produced changes in fetal behavior typically resulting in a decrease in fetal movements in most cases. Although, other variables had a high probability (>90%) of influencing fetal behavior, they did not produce a consistent pattern of response. In conclusion, a methodologically robust study protocol was designed, demostrating good interobserver agreement. The study showed a general decrease in fetal movements and facial expressions in response to the “chaos” and “fast speed” stimuli based on prosodic alterations of the maternal voice. This response is interpreted as a sign of fetal attention to a novel stimulus. However, due to complexity of the sound stimuli and the methodology used, it is challenging to correlate specific fetal movements with individual musical elements, warrating further research in this area.