Objective To assess fetal behavioral changes in response to vibroacoustic stimulation (VAS) in normal singleton pregnancies using four-dimensional (4D) ultrasound. Methods Ten types of fetal movements and facial expressions in 68 healthy pregnant women between 24 and 40 weeks were studied using 4D ultrasound for 3 min before and after 3-s VAS. The frequencies of mouthing, yawning, tongue expulsion, back arch, jerky arm movement, startle movement, smiling, scowling, hand-to-face movement, and blinking were evaluated. The fetuses were subdivided into four gestational age groups (24-27, 28-31, 32-35, and ≥36 weeks). Comparison of the frequencies of the fetal behaviors before and after the stimulation in each gestational age group was conducted to detect the response to stimulation with advancing gestation. Results There were no significant differences in the frequency of each fetal behavior before and after VAS at 24-27, 28-31, and 32-35 weeks of gestation. However, the frequencies of blinking and startle movements were significantly higher after VAS in the 36-40 gestational age group (P < 0.05). Conclusion The age of 36 weeks of gestation might represent an advanced stage of brain and central nervous system development and maturation as the response to stimuli is prominent at this age compared with earlier gestation.
Keywords: 4D ultrasound; fetal CNS development; fetal CNS maturation; fetal behavior; fetal stress; vibroacoustic stimulation.