[A national survey on physical growth and development of children under seven years of age in nine cities of China in 2015].

Objective: To investigate and analyze the status of physical growth and its change in children under 7 years of age in 9 cities of China, and to provide scientific data for renewing and developing the new growth reference of Chinese children.
Methods: Data of healthy children under 7 years of age were collected by stratified cluster sampling method in Beijing, Harbin, Xi'an, Shanghai, Nanjing, Wuhan, Guangzhou, Fuzhou and Kunming during the period from June to November in 2015. They were divided into 22 age groups. The sample size of boys or girls, urban or suburban was 150-200 in each age group in each city, and the total sample size in the 9 cities was 161 774. Weight, length/height, head circumference, sitting height, chest circumference and waist circumference were measured by the trained investigators using standard methods. There were strict quality control measures during investigation process. The t test was used to compare the difference of physical growth between two groups and one-way ANOVA was used to compare the difference of physical growth among three groups.
Results: (1) The level of physical growth of children under 7 years were different between boys and girls, urban and suburban, as well as different regions of China in 2015. The urban-suburban difference was more significant in children older than 8 months, that is, the weight and height of urban children were greater than those of suburban children (0.01-0.48 kg and 0.1-1.1 cm respectively). (2) Weight and height of children in the 9 cities, whether urban or suburban areas, had been greater than WHO growth standards, for example, the Z-scores of height values of urban and suburban children were 0.43 ±0.99 (t=130.551, P<0.05) and 0.30 ±1.01 (t=87.407, P<0.05) higher than the WHO standards. (3) The physical growth of children in the 9 cities was improved in varying degrees during the past 10 years. For example, the changes of weight and height in urban children under 3 years were not significant, while there was significant improvement among children older than 3 years and the increasing trend became apparent along with the increasing of age (0.05-1.18 kg in weight and 0.5-1.8 cm in height). The urban-suburban difference of physical growth in each age group of boys and girls narrowed significantly during the past 10 years, which was clearly shown from the narrowing urban-suburban differences of weight and height in boys aged 5.5-<6.0 years (1.58 kg in 2005 vs. 0.44 kg in 2015 and 2.8 cm in 2005 vs. 0.9 cm in 2015) . (4) From the increments of each decade during 1975-2015, a rapid increments of physical growth during 1975-2005 were found, while the increments after 2005 had slowed comparing with that of the previous period in urban areas, for example, the increments of height in boys aged 5.5-<6.0 years were 1.5, 2.1, 2.7, 0.7 cm respectively in the 1(st), 2(nd), 3(rd) and 4(th) decade (1975-1985, 1985-1995, 1995-2005, 2005-2015) . In suburban areas, the trends of the previous 3 decades were similar with that of urban children, while the increments of the 4(th) decade were still bigger though they were slightly smaller than those of the 3(rd) decade, for example, the increments of height in boys aged 5.5-<6.0 years were 2.4, 2.3, 3.2, 2.6 cm in the 1(st), 2(nd), 3(rd) and 4(th) decade respectively. Conclusions: Physical growth of children under 7 years of age showed a slow positive secular trend during the last decade after a rapid increase. The increments of suburban children's physical growth were greater than those of urban children. The physical growth of children under 7 years in 9 Chinese cities exceeded the WHO standards.