Fetal movement refers to motion of a fetus caused by its own muscle activity. Locomotor activity begins during the late embryological stage, and changes in nature throughout development. Muscles begin to move as soon as they are innervated. These first movements are not reflexive, but arise from self-generated nerve impulses originating in the spinal cord. As the nervous system matures, muscles can move in response to stimuli.
Generally speaking, fetal motility can be classified as either elicited or spontaneous, and spontaneous movements may be triggered by either the spine or the brain. Whether a movement is supraspinally determined can be inferred by comparison to movements of an anencephalic fetus.
Although the heart begins to beat on the 23rd day after conception, this article primarily deals with voluntary and reflex movements. Ages are given as age from fertilization rather than as gestational age.
Some sources contend that there is no voluntary movement until after birth. Other sources say that purposive movement begins months earlier. 3D ultrasound has been used to create motion pictures of fetal movement, which are called "4D ultrasound".
Read more about Fetal Movement: Variation in Activity Level, Monitoring Fetal Movement
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