During a well-child examination, which measurement helps determine microcephaly?

Head circumference is the critical measurement used to determine microcephaly, which is a condition characterized by an unusually small head size in relation to an age-appropriate standard. This measurement is essential during well-child examinations because it allows healthcare professionals to assess brain growth and development. A head circumference that falls significantly below the expected range for a child's age and sex may indicate possible developmental issues or abnormalities in brain growth.

Collecting head circumference data helps identify microcephaly early on, which can then lead to further evaluation and intervention if needed. While weight, height, and chest circumference provide important information about a child’s overall health and growth trajectory, they do not specifically address the development of the brain as directly as head circumference does. This makes head circumference the pivotal measurement for assessing conditions like microcephaly.