Scarf ratio: A method of measuring the Scarf sign in preterm born infants.
A new method of measuring the Scarf sign called the Scarf ratio is described in which data derived were reported on a continuous scale. The Scarf ratio is the distance of the olecranon process of the arm being tested as it moves across the trunk compared with the infant's own biacromial width. Longitudinal data for the Scarf ratio were measured in a cohort of 111 Thai preterm born infants. The data were collapsed into four age ranges ie 28-31, 32-36, 37-39 and 40 weeks post-conceptional age (PCA) according to the trends from the longitudinal plots. As the means of the Scarf ratio increased with age, it can be described that the resistance to the passive movements of the arm increased when the infants grew up. Data were also converted to a newly developed categorical scoring system. All infants between the age of 28 and 31 weeks PCA recorded a score of 1 (low tone). Most infants aged 32-36 and 37-39 weeks PCA recorded a score of 2 while most infants aged 40 weeks PCA obtained a score of 3 (high tone). Thus, this method can be an alternative when continuous data for the Scarf sign are desirable.