New Finnish reference for head circumference from birth to 7 years

Background and objectives. In the evaluation of the growth of head circumference (HC), charts depicting normal growth are of paramount importance. Current Finnish HC growth charts are based on data from only 130 children born 1953-1964. As a secular trend in HC growth has been reported, we updated the HC charts using a large sample of contemporary HC data. Material and methods. Mixed cross-sectional HC data of 19,715 healthy subjects aged 0-7 years were collected from primary health care providers. References for HC for age and HC/height ratio for age were fitted using generalized additive models for location, scale, and shape (GAMLSS). Results. Increased HC for age was seen particularly after 2 years of age in both genders compared to the 1953-1964 reference. The SD for HC was remarkably larger in the 1953-1964 reference. The proportion of 1986-2008 reference subjects exceeding the + 2 SD limit of the 1953-1964 reference was much bigger than the proportion below -2 SD. Conclusions. Because of the secular change in HC growth, the HC reference has to be renewed periodically. The new Finnish reference for HC for age should be implemented for monitoring HC growth of children in Finland.