Revised birth centiles for weight, length and head circumference in the UK-WHO growth charts

Background: The adoption in May 2009 by the UK of the WHO 2006 standard necessitated the provision of UK-based birth centiles for pre-term infants. The pre-existing British 1990 reference birth centiles, used in the UK since 1995, had been biased by the inclusion of post-natal data. Aim: To describe the construction of new UK birth centiles for weight, length and head circumference, based on British 1990 reference data, but excluding post-natal data. Subjects and methods: Birth data from the five original studies, collected between 1983-1993, were pooled and analysed by the LMS method, for the sexes separately. In addition, sex-specific composite centiles were constructed for infants born at term (37-42 completed weeks). Results: The birth data included 9443 weights, 985 lengths and 1841 head circumferences, covering 23-44 weeks gestation. The analysis provided LMS tables defining reference centiles for weight and head circumference from 23-42 weeks and for length from 26-42 weeks. The term centiles are for use at age 0 on the post-natal 0-1 year chart. Conclusion: These new centiles, replacing those of the British 1990 reference, are more accurate than their predecessors which were biased due to the inclusion of post-natal data.