Seasonality of growth in Shanghai infants ( n =4128) born in 11 consecutive years

Objective: To describe the seasonal growth patterns in Shanghai infants, to explore seasonal time lag between weight gain and length gain, and to investigate the long-term effect of birth season on early postnatal growth. Design: Community-based longitudinal study. Setting: Shanghai, People's Republic of China. Method: Children were followed up monthly from I to 6 months, 3 monthly from 6 to 12 months, and 6 monthly from 12 to 24 months. Subjects: A total of 6018 children born between I January 1980 and 31 December 1990. Main outcome measures: Weight gain, length gain and change in body mass index (BMI) over the seasons of the year. Results: The infants tended to grow faster in height in spring and summer, and faster in weight and BMI in autumn and winter. The seasonal effect on weight gain and length gain is largely independent. The mean length value at 1 month of age was about 2.0 cm higher in infants born in May to July than in those born in November to February. At 24 months of age this difference was reduced to about 0.7 cm. Conclusions: There is a clear and consistent seasonality in growth in Shanghai infants. The seasonality seems to act independently on weight and length. Birth month has some association with attained size, but this is reduced during the first 2 y of life. Sponsorship: Children's Hospital of Shanghai Medical University, Shanghai; The University of Hong Kong, Hong Kong SAR.