Newborns who become lighter in weight in 12 days, with a decrease ranging from 3% to 9% of birth weight, are mostly normal; if the decrease ranges more than 10%, it is necessary to pay attention to the possibility of disease. Newborns in the first week after birth due to insufficient milk intake, water loss, meconium discharge, etc., there may be a temporary weight loss, or known as physiological weight loss, about 3 ~ 4 days after birth to reach the lowest point, the decline range of 3% ~ 9%, and then gradually rebound, to the 7th to 10th day of life should be restored to the birth weight. It should be returned to the birth weight in 7~10 days after birth. The weight loss of a newborn baby in the first 12 days of life may be normal within this range. If the baby’s weight loss exceeds 10% or does not return to birth weight, it is a pathological condition, such as prolonged diarrhea and other diseases. Prompt medical attention is required for evaluation by a specialist and targeted management or treatment. If you find that your newborn continues to lose weight, you need to consult your doctor for symptomatic management or treatment to ensure the healthy growth of your newborn.