Objective: Very little is known about functional brain-behavior relationships before birth. In an exploratory study of fetal blood flow and fetal behavior several novel findings were made using Hierarchical Linear Modelling (HLM) and mediator-moderator analysis of hemispheric dominance and fetal movement responses to vibratory stimulation. Method: A healthy sample of 313 human fetuses between 20–40 weeks gestation were enrolled in a longitudinal study of hemispheric dominance and movement responsiveness. A Color Doppler Energy (CDE) protocol was used to measure fetal blood flow velocity in the right and left middle cerebral arteries (RMCA and LMCS respectively). Results: Findings revealed a linear increase in perfusion of the two hemisphere from 20–40 weeks, (p < 0.001), lateral differences in the rate of perfusion between the hemispheres, and a shift in dominance (level of perfusion) from the left to right hemisphere at 30 weeks gestation. Moreover, during an experimental procedure of vibratory stimulation, baseline fetal movement is predictive of post-stimulation movement. The effect is moderated by blood flow velocity in both hemisphere which itself is mediated by gestation age, (p < 0.01). Conclusion(s): These findings show a dynamic relationship of brain perfusion prior to birth, phenotypic shifts in dominance of probably genetic origin and control of fetal movement that is influenced by brain asymmetry, activity, and maturity. A model of asymmetric control of movement is postulated as the operative mechanism secondary to a more rapidly developing right cerebral hemisphere.