[Survey on gross motor development of infants in nine cities of China in 2015]

Objective: To analyze the current situation of gross motor development of infants in nine cities of China and their relationship with physical growth. Methods: Healthy full-term infants aged 1-24 months were investigated by cross-sectional survey, which was carried out in nine cities (Beijing, Harbin, Xi'an in northern, Shanghai, Nanjing, Wuhan in central, and Guangzhou, Fuzhou, Kunming in southern regions of China) from June to October in 2015. Subjects were grouped into 12 age groups (1-<2, 2-<3, 3-<4, 4-<5, 5-<6, 6-<8, 8-<10, 10-<12, 12-<15, 15-<18, 18-<21, 21-<24 months). Gross motor development of infants was examined by fieldworkers and the information on parental education, family income and birth status were obtained by questionnaire. Weight, length and head circumference was measured by fieldworkers according to standard methods in the fields and their Z scores were calculated by using WHO growth standard. Z scores of weight (WZ), length (LZ) and head circumference (HCZ) <-2 s was considered as lower group, -2 s-<-1 s as medium-lower group, -1 s-1 s as medium group, 1 s-<2 s as medium-higher group and ≥2 s as higher group. The age of gross motor development was calculated by Probit regression analysis and χ(2) test was used for comparison of categorical data. Results: (1) The number of infants whose gross motor development was examined were 88 968 in the nine cities. The proportion of achievement of motor development became larger with the chronological age, i.e. it was 11.1% (800/7 236) at 5-<6 months, 65.2% (4 921/7 545) at 6-<8 months and 98.5% (7 417/7 531) at 8-<10 months for sitting alone without support. There was no gender difference in the proportion of achievement of sitting alone without support, hand-knee crawl, stand alone and walk alone (χ(2)=2.873, 0.275, 0.250, 0.576, all P>0.05). (2) The median age of achievement of sitting alone without support, hand-knee crawl, stand alone, walk alone was respectively 5.9, 7.8, 10.8, 13.0 months, and their ranges from 1(st) to 99(th) percentile were respectively 4.2-8.3 months, 4.9-12.6 months, 7.6-15.4 months, 9.8-17.4 months. The gender difference of median age of gross motor development was 0.0-0.1 months and their regional difference was 0.0-0.7 months. (3) In the lower weight group, their median age of sitting alone without support and walk alone were 0.2-0.6 months later than the medium weight group, while their median age of hand-knee crawl and stand alone were similar to those of the medium weight group. In higher weight group, the median age of sitting alone without support and stand alone were similar to that of the medium weight group, while their median age of hand-knee crawl was 0.3 later months and their median age of walk alone was 0.3 months earlier than that of the medium weight group. There was no significant relationship between length and the age of sitting alone or standing alone (the difference was 0.0-0.2 months in each group). The median age of hand-knee crawl and walk alone was 0.4-0.7 months later in lower length group than in other length groups. The median age of gross motor development was similar among different head circumference groups (0.0-0.2 months). The relationship between weight/length and motor development was similar to that between weight and motor development. Conclusions: There were no gender difference and slightly regional difference in the age of achievement of gross motor skills. The percentile age of gross motor skills helps to understand the population variation in healthy infants. The gross motor development is related with weight, length and body proportion.