Conditional reference charts to assess weight gain in British infants.

Growth monitoring in infancy is a useful tool for detecting growth disorders and failure to thrive. However, current weight charts do not monitor growth as such, they only identify infants whose weight centile is low and/or falling. A reference of conditional weight gain is described which compares an infant's current weight with that predicted from their previous weight, allowing for the fact that on average, light infants tend to grow faster than heavier infants. The reference, which expresses conditional weight gain as an SD score of centile, is based on the UK 1990 weight reference supplemented with correlation data on 223 infants from the Cambridge Infant Growth Study measured regularly between 4 weeks and 2 years of age. The reference is validated with data on 727 infants from the Newcastle Regional Health Authority database. The conditional reference provides a valid assessment of the weight gain of British infants, over time periods of four or more weeks, throughout the first two years of life.