The causes of three-month-old babies’ jerking are: physiological conditions, brain injury, etc. 1. Physiological conditions: three-month-old babies in the prone position, the head elevation is normal, can turn freely, in the emergence of certain physiological needs, such as hunger, want parents to hold, etc., or by the stimulation of the state of lying down in a flat, vertical holding, crying, head tilted back, jerking is normal, parents do not need to worry too much. 2. Brain injury: babies lying down with frequent head tilting, jerking, accompanied by crying, body stiffness, poor quality of sleep, or even difficulty in falling asleep, feeding difficulties, prone position when the head raised higher, but the head can not be freely rotated in this case is to pay attention to the consideration of the possibility of brain injury caused by. In addition, there are other reasons that can lead to similar symptoms in three-month-old babies, it is recommended to seek timely medical attention to identify the cause of the disease for timely intervention to ensure the normal growth and development of the baby.