Physical measurements of Chinese children in Hong Kong

Abstract

Background: Growth is defined as an increase in size over time. It is the essence of the developing organism. Growth of different parts of body follow a predictable schedule in normal development and any disturbance, genetic or environmental, will lead to disproportion of physical features. Most syndromes with dysmorphic features demonstrate recognizable patterns of disproportionate growth and thus physical measurement is important in the evaluation of children and adults with dysmorphic features and/or structural anomalies. In order to delineate if growth of a person is normal, a reference must be used for comparison. However the currently available reference data are mostly derived from children of restricted ethnic and geographic background which has been shown to be not equally applicable to all children due to substantial ethnic variability. Regional specific data for body parts is necessary to establish accurate reference for different ethnicities which is limited beyond the neonatal period. The aim of our pilot study is to obtain a set of region specific physical measurements of Chinese children from kindergartens in Hong Kong.

Methods: In this cross-sectional study, we recruited children between 2 to 6 years old from kindergartens in Hong Kong. Consent for participation was obtained from school principal and informed consent was obtained from parents for each participant. Other than the 24 growth parameters included in the “Neonatal anthropometry for the Chinese” by Fok et al, we included 3 other parameters and followed the definition and instruction of measurements recommended by the same book as well as the “Handbook of Physical Measurements” by Hall et al. with minor modification. Measurement of penile length was not performed due to objections from schools and thus only 26 parameters were measured. Three measurers performed the measurements in kindergartens. They received training from a clinical geneticist and have achieved a satisfactory inter-rater reliability in a training cohort for each parameter before starting the study. The raw anthropometric data collected were then normalized and fitted into a model by LMS method. A growth curve was plotted for each of the 26 anthropometric measurements.

Results and Discussion: For inter-rater reliability, an average Cronbach’s alpha of 0.927 (excellent internal consistency) were achieved. We recruited a total of 439 children between 3 to 6 years old from 5 participating kindergartens, 3 in Kwai Tsing District and one each in Kowloon City and Yuen Long Districts. Two year-olds were excluded due to small sample size. There are a total of 244 boys and 195 girls. Subjects were grouped according to their age. The number of subjects in each age group were: 3 years old: 112 (57.1% male); 4 years old: 160 (51.3% male); 5 years old: 131 (54.2% male); and 6 years old: 36 (75% male). Since no difference were observed between male and female in all of the measurements, therefore data were combined when plotting growth curves. The 3rd, 10th, 25th, 50th, 75th, 90th and 97th percentile lines were presented in the growth curves.

Significant differences were identified compared to the Caucasian data in different important growth parameters including the outer canthal distance, the inner canthal distance, facial width, facial height and sternal length. Our current pilot study presents the first local and ethnicity specific data on physical measurements on children between the ages of 3 to 6 years old. And important differences are noted in the growth parameters between local Chinese children and their Caucasian counterparts. Of all the comparisons, the biggest differences existed in the measurement of facial width and facial height. For facial width, the -2 standard deviation of the Chinese coincided with the +2 standard deviation of the Caucasian data. Our findings highlighted the substantial ethnic variability in physical measurement and thus the need for an ethnic-specific reference for Chinese children. A more comprehensive study including more Chinese children and adults of different age groups is warranted to capture the full-spectrum ethnic-specific population reference in a longitudinal manner.