Four-month-old baby old leg lifting may be too heavy blanket, excitement and other physiological factors, or consider vitamin D deficiency and other diseases caused by. 1. Physiological factors: If the baby covers a thicker blanket, causing the baby discomfort, or emotional excitement, the four-month-old baby can appear to lift his legs. If not accompanied by other symptoms of discomfort, more normal phenomenon, no need to worry. 2. Vitamin D deficiency: Vitamin D deficiency may be caused by insufficient perinatal reserves, insufficient sunlight and other factors. Affected children will show symptoms such as excessive sweating, irritability, crying and muscle relaxation. Babies often show increased neural excitability, and there will be a four-month-old baby’s old leg lifting. Four-month-old baby lifting legs, there may be other reasons, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.