5 months baby suddenly urinate less may be physiological factors, gastrointestinal diseases, kidney disease, urinary stones and other factors. 1. Physiological factors: the baby ate too little milk, and the weather is hot, sweating more, urine production is too small, will lead to a sudden urine, and the urine color will become dark yellow, accompanied by a mild odor. 2. Gastrointestinal diseases: for example, acute gastroenteritis, the onset of acute, frequent vomiting and diarrhea can make the baby, resulting in a decrease in body fluids, urine production is reduced, which will lead to sudden urinary. 3. Kidney disease: 5 months baby suddenly urinate less may also be related to kidney disease, such as acute glomerulonephritis, can lead to water and sodium retention, urine will suddenly reduce, accompanied by lower limbs and eyelid swelling, proteinuria and other abnormal manifestations. There may be other reasons why a 5-month-old baby suddenly urinates less, so it is recommended to go to the hospital in time, complete the examination to clarify the cause of the disease, and then give targeted treatment under the guidance of the doctor.