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.