Sex differences in weight in infancy and the British 1990 national growth standards.

OBJECTIVES: To determine if there is a sex difference in infancy in the new British national standards for weight (based on data from 1990). DESIGN: Weight data in a birth cohort were compared with the 1990 standards and Tanner and Whitehouse (1966) standards up to age 12 months. SETTING: Newcastle upon Tyne. SUBJECTS: 3418 term infants. RESULTS: Our cohort showed a mean difference in standard deviation scores of 0.42 between boys and girls (P < 0.0001) when compared with the 1990 standards. Two and a half times as many girls as boys had weights below the 3rd centile during the first year, with an equivalent excess of boys above the 97th centile (P < 0.0001). Similar results were found with Tanner and Whitehouse standards. CONCLUSIONS: These differences could result in substantial sex bias in the identification of poor growth in early childhood. The standards need modification.