Mid-arm circumference and mid-arm/head circumference ratio in term newborns

CONTEXT: Mid-arm circumference of the newborn is strongly associated with birth weight and is a very good indicator of low and insufficient birth weight. However, there are few Brazilian studies on the relationship between mid-arm and head circumferences and, thus, this does not form part of the routine evaluation for newborns. OBJECTIVES: To establish the mid-arm circumference and mid-arm/head circumference ratio in a population of term newborns. TYPE OF STUDY: Cross-sectional study carried out between June 1997 and August 1999. SETTING: Hospital Maternidade Leonor Mendes de Barros, São Paulo. PARTICIPANTS: Term newborns (66 males and 65 females) of appropriate growth for gestational age, whose mothers were healthy, were included in the study. MAIN MEASUREMENTS: Arm circumference, arm circumference/head circumference ratio, birth weight and gestational age were measured within 48 hours of birth. Data were considered significant when p < 0.01. RESULTS: The mean values for the mid-arm circumference were 10.76 cm (standard deviation, SD = 0.68) for females and 10.76 (SD = 0.81) for males. The mean value for the mid-arm/head circumference ratio was 0.31 (SD = 0.02) for both sexes. Mid-arm circumference values were significantly related to birth weight and gestational age, whereas mid-arm/head circumference ratio was related only to birth weight. CONCLUSIONS: Mid-arm circumference and mid-arm/head circumference ratio values were established for the studied population. It was possible to obtain curves for both mid-arm circumference and mid-arm/head circumference ratio in relation to birth weight. However, for mid-arm circumference, it was only possible to obtain curves in relation to gestational age. The use of the regression curves did not seem powerful enough to predict the mid-arm circumference and mid-arm/head circumference ratio in this population of term newborns. There were no gender differences for either of the measurements studied