New Argentine head circumference references for people with achondroplasia from 0 to 21 years of age.

Introduction. Macrocephaly is a phenotypic feature of achondroplasia (ACH), the most common form of disproportionate short stature. In 2011, we published head circumference (HC) references for this population, but due to the scarcity of data about older ages, the centiles were estimated only up to 6 years of age. Objective. To estimated centiles of the HC between birth and 21 years of age for ACH. Population and methods. Data from children with ACH assisted between 1992 an 2024 at a thirdlevel hospital in Argentina were used for its estimation. The growth curves were adjusted using the LMS method. To evaluate the magnitude of the differences between the Argentine references of ACH and those of the general population, the 3, 50, and 97 centiles at different ages were plotted comparatively. Results. The HC of ACH was more significant at all ages than the general population's references. During the first year of life, males and females reach 84% and 86% of adult size, respectively, completing growth after 20 years of age. Conclusions. Due to the difference in cephalic size between the general population and ACH, it is essential to have specific references for this population. This will allow us to detect growth trajectories not attributed to ACH and to suspect deviations that require a rapid interdisciplinary approach.