At birth, total body water represents approximately what percentage of body weight in a full-term infant?

• A. 60%
• B. 75%
• C. 90%
• D. 80%

Answer: (B)

In newborns, total body water is very high because they have little fat and a large proportion of their body fluids are extracellular. For a full‑term infant, total body water is about three-quarters of body weight. This high TBW helps explain fluid balance in the newborn and gradually declines with age toward the adult level of about 60%. Among the options, about 75% best matches the typical value used for term infants. (80% is also plausible as a rough range, but 75% is the standard figure cited.)