Aims: To assess the responsive fetal extremity movement to vibro-acoustic stimulation test (VAST).
Methods: The moving velocity of fetal femur was assessed after VAST by pulsed Doppler device. The ultrasonic beam was insonated at a right angle to the fetal femur. The following parameters were determined: limb retreat velocity in accelerative slope (Pk1); limb replenishment velocity in decelerative slope (Pk2); mean flexion to extension velocity; and the response time to VAST. Among 80 normal singleton pregnancies in 33-41 weeks, 68 were weekly evaluated and the others were assessed for two or more times during the study period, for a total of 680 studies of fetal kinetics.
Results: The Pk1 declined from 9.6 to 6.26 cm/s; Pk2 decreased from 2.6 to 1.3 cm/s; mean velocity was reduced from 6.0 to 4.25 cm/s; whereas the response time increased from 0.1 to 0.3 s throughout the study period, i.e., fetal response reduces and the response time increases as maturation progresses.
Conclusion: The pulsed Doppler may assess fetal activity in any body structure. Reflex responses become slow and complex on both the velocity and response time as maturation increases with gestational age. Our observations have resulted in a novel and easy method for the quantitative assessment of fetal reflex reactivity to external stimuli.