The effect of vibratory acoustic stimulation on fetal middle cerebral artery impedance and instantaneous fetal heart rate: A prospective cross-sectional study from 20 to 42 weeks' gestational age

Objective: We sought to examine the response of fetal heart rate (FHR) and middle cerebral artery resistance (MCA PI) to vibratory acoustic stimulation (VAS). Methods: We examined 160 normal pregnant women with uncomplicated pregnancies. We obtained baseline measurements of FHR and MCA PI before the application of a 3-s vibratory acoustic stimulus (commercially available artificial larynx); we then measured FHR and MCA PI change immediately after the stimulus. Real time ultrasonography with pulsed wave and color Doppler imaging was used for the execution of the study. Statistical evaluation was performed by comparison of the means and regression analysis. Results: Fetuses less than or equal to 28 weeks did not exhibit any significant change in their heart rate or MCA PI after VAS (143 +/- 2 vs 145 +/- 2 for heart rate and 1.75 +/- 0.07 vs 1.71 +/- 0.07 for the MCA PI; P = not significant). Fetuses >28 weeks responded with significant changes (140 +/- 1 vs 153 +/- 1 for heart rate and 1.57 +/- 0.03 vs 1.30 +/- 0.03 for MCA PI; P < 0.001). Regression analysis revealed that FHR and MCA exhibited variable patterns of response to VAS with advancing gestation. Conclusion: As the human fetus matures, its response to external VAS varies. FHR response follows a different pattern than MCA PI. Increasing auditory function and parasympathetic nervous system activity are thought to be important in the development of this gestational age-dependent pattern.