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 a nd MCA PI before the application of a 3-s vibratory acoustic stimulus (commercially available artificial larynx); we then measured FHR and M CA 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 t he 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 < 0.00 1). Regression analysis revealed that FHR and MCA exhibited variable p atterns of response to VAS with advancing gestation. Conclusion: As th e human fetus matures, its response to external VAS varies. FHR respon se follows a different pattern than MCA PI. Increasing auditory functi on and parasympathetic nervous system activity are thought to be impor tant in the development of this gestational age-dependent pattern.