[Percentile reference value of waist circumference for Chinese children aged 3-7 years]

Objective: To study and establish the percentile reference values of waist circumference (WC) for Chinese children aged 3-7 years. Methods: A total of 26 480 children aged 3-7 years were collected as part of the National Survey on Physical Growth and Development of Children in nine cities (Beijing, Harbin, Xi'an, Shanghai, Nanjing, Wuhan, Guangzhou, Fuzhou and Kunming) in China from June to November 2015. Sex- and age-specific smoothed percentile reference values of WC were established using the Lambda Mu Sigma method. The P(75) and P(90) curves of WC for children aged 3-7 years in this study were linked with the published P(75) and P(90) cut-off points for Chinese children and adolescents aged 7-18 years. The P(50) percentile of WC in this study was compared with the corresponding percentiles of several foreign studies. Results: The P(5), P(10), P(15), P(20), P(25), P(50), P(75), P(80), P(85), P(90) and P(95) reference values of WC were obtained for boys and girls aged 3-7 years biannually, at the interval of every six months. Results showed that WC at the P(50) had significantly increased from 47.5 cm at the age of 3 to 54.2 cm at the age of 7 for boys and from 47.0 cm at the age of 3 to 52.2 cm for girls at the age of 7. The corresponding WC percentile values appeared a bit higher in boys than those in girls at the same age, with the differences from 0.4 to 3.6 cm. The differences between measured and fitted WC at each empirical percentile ranged from -0.3 to 0.5 cm for both boys and girls aged 3-7 years. The P(75) and P(90) values of WC for boys and girls aged 3-7 years in this study presented a consistent, continuous tendency on age with the published WC cut-off points (P(75) and P(90)) for Chinese children and adolescent aged 7-18. The increasing trend of WC by age in Chinese children aged 3-7 years was consistent with those of foreign studies, at the middle level for boys and lower middle level for girls. Conclusions: Through this study, we established the WC percentile values for Chinese children aged 3-7 years and achieved the continuity in age with the published WC cut-off points for Chinese children and adolescents aged 7-18. These established WC percentile values can be used as reference for clinical practice, health care and scientific research.