A new study finds that classical music exposure in the third trimester reduces the complexity of fetal heart rate variability, leading to more regular and stable cardiac patterns, potentially linked to fetal movements.
Study: Response to music on the nonlinear dynamics of human fetal heart rate fluctuations: A recurrence plot analysis. Image Credit: MVelishchuk/Shutterstock.com
In a recent study published in Chaos, a group of researchers assessed the response of classical music exposure to the nonlinear behavior of fetal heart rate fluctuations in fetuses between 32 and 40 weeks of gestation using recurrence quantification analysis.
Background
Can an unborn baby hear and respond to music? Studies suggest that fetuses begin processing sound as early as the third trimester, with music potentially influencing neurodevelopment. Music has long been recognized for its influence on physiological and psychological states.
It has been used in therapeutic settings to reduce stress, improve cognitive function, and regulate emotional responses. Studies suggest that music exposure in utero may contribute to fetal neurodevelopment, potentially impacting sensory processing and autonomic regulation.
Fetal heart rate variability (HRV) is a key indicator of autonomic nervous system development, reflecting the balance between sympathetic and parasympathetic activity. Traditional analyses of fetal HRV rely on linear methods, which may not fully capture its complexity.
Recurrence quantification analysis (RQA) has emerged as a valuable tool in understanding the nonlinear dynamics of physiological systems, offering deeper insights into fetal responses to external stimuli.
Despite promising findings, limited research exists on how music influences fetal HRV through nonlinear analysis. Further research is needed to clarify the extent to which musical stimulation modulates fetal autonomic activity.
About the study
The present study was conducted at Hospital Reina Madre Clínicas de la Mujer in Toluca, Mexico, between April and July 2024. A total of 100 pregnant women in their third trimester (28-40 weeks of gestation) were selected.
Inclusion criteria required singleton pregnancies without complications, while exclusions included multiple gestations, fetal malformations, drug use, and pregnancy-related conditions such as gestational diabetes or hypertension. Ultimately, 37 fetal R-R time series met the quality criteria and were analyzed.
Participants were seated comfortably while a Monica AN24 maternal-fetal monitor, operating at a 900 Hz sampling frequency, recorded transabdominal fetal electrocardiograms. Five strategically placed electrodes ensured optimal signal acquisition.
Before placement, the abdominal skin was cleaned and prepared to reduce impedance. Musical stimulation was applied through headphones placed on the maternal abdomen, delivering two five-minute segments of classical music representing European and Mexican classical compositions, respectively. The study followed a fixed sequence: PRE (baseline, no music), STIM1 (first musical piece), STIM2 (second musical piece), and POST (post-stimulation).
RQA was used to analyze fetal HRV, extracting key indices such as determinism (DET), average diagonal line length (L), maximum line length (LMAX), entropy (ENTR), and trapping time (TT).
Additionally, conventional HRV indices, including the standard deviation of R–R intervals (SDRR), were evaluated. Statistical analyses were performed using GraphPad Prism, with significance set at p ≤ 0.05.
Study results
Among the 100 recorded cases, 57 fetal R–R time series were excluded due to excessive data loss, and six more were eliminated due to gestational diabetes. This resulted in 37 eligible cases for analysis across all study stages.
Maternal and fetal demographic data indicated an average gestational age of 36.2 ± 3.2 weeks and a mean maternal age of 29.2 ± 6.0 years. The mean maternal weight was 74.6 ± 13.7 kg, while the mean height was 1.64 ± 0.10 m.
The newborns had an average birth weight of 3149 ± 394 g, and the median Appearance, Pulse, Grimace, Activity, and Respiration (APGAR) score at five minutes was 8.8 ± 0.5.
The cumulative number of fetal heart rate accelerations varied across the study phases. The PRE and STIM1 stages each recorded 24 accelerations, STIM2 showed a slight reduction to 21, while POST exhibited a notable increase to 31. No fetal heart rate decelerations were observed during any phase.
RQA indices revealed significant modifications in fetal HRV. DET increased significantly from PRE (0.455 ± 0.135) to POST (0.514 ± 0.138, p = 0.0117), indicating a shift toward greater regularity and predictability in fetal cardiac dynamics. Similarly, L values rose from PRE (2.52 [2.32-2.82]) to POST (2.67 [2.44-3.13], p = 0.0414) and STIM2 (2.58 [2.38–2.96], p = 0.0238), suggesting increased stability.
LMAX values demonstrated a marked increase from PRE (10.0 [8.5-15.0]) to STIM2 (17.0 [9.0-33.5], p = 0.0037), reinforcing the observation that the second musical stimulus enhanced the predictability of fetal heart rate patterns.
TT also showed a significant rise, further supporting the hypothesis that musical exposure influences the fetal autonomic system. Conversely, ENTR declined from PRE to POST, reflecting reduced complexity and nonlinear fluctuations in fetal HRV.
The SDRR index exhibited an increase from STIM1 (18.81 ± 6.84 ms) to POST (21.94 ± 7.93 ms, p = 0.0464), suggesting enhanced overall fetal HRV post-exposure. Although spectral indices, including the low-frequency (LF) and high-frequency (HF) components, showed trends toward change, they did not reach statistical significance.
Conclusions
To summarize, this study provides compelling evidence that classical music exposure influences fetal HRV by enhancing regularity, predictability, and stability in cardiac dynamics. The observed increase in DET and decreased ENTR suggests a shift toward more structured autonomic responses post-stimulation.
Notably, the second musical stimulus elicited the most pronounced effects, highlighting the potential for specific musical characteristics to shape fetal responses.
The increase in SDRR in the post-exposure phase aligns with previous findings associating fetal movement with heightened variability, suggesting that music may not only modulate autonomic control but also influence fetal behavioral states. These insights underscore the potential of prenatal music exposure as a non-invasive means of supporting fetal development.
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