How can I differentiate between physiological and pathological weight loss in the first week of life for a newborn infant?

Physiological weight loss in a newborn during the first week of life is common and usually relates to body fluid adjustments. It typically involves a weight loss of less than 10% of birth weight, stops after about 3 or 4 days, and most infants regain their birth weight by 3 weeks of age.

Pathological weight loss is suggested if the infant loses more than 10% of their birth weight in the early days of life or fails to regain birth weight by 3 weeks. In such cases, a clinical assessment should be performed to look for dehydration, illness, or feeding problems. A detailed feeding history and direct observation of feeding by trained personnel are recommended. Further investigations should be guided by clinical findings.

Weight should be measured at appropriate intervals but not more frequently than daily if there is concern. Feeding support should be provided if weight loss exceeds 10%, and referral to paediatric services considered if there is marked weight loss, evidence of illness, or failure to respond to feeding support.