OBJECTIVE: To explore the association between birth season and physical development and provide a necessary reference value to inform the implementation of public health services. DESIGN: Cross-sectional study. SETTING: Forty-five counties in ten provinces in western China in 2005. SUBJECTS: A sample of 13,387 children under 3 years old and their mothers were recruited using a stratified, multistage, cluster random sampling method. RESULTS: The results of the circular distribution analysis suggested that stunting and underweight exhibited time aggregation (Z = 32.57, P<0.05; Z = 10.42, P<0.05) among children under 3 years old. The Z - value for wasting, however, was not statistically significant (P>0.05). The generalized linear mixed models showed that children born in the summer were less likely to exhibit stunting (OR: 0.74~0.97) than were children born in the winter after adjusting for confounders, but no significant differences were identified for the other seasons. In addition, among children aged 25 to 36 months, those born in the summer and autumn were less likely to exhibit stunting after adjusting for confounders than were children born in the winter, but the association between birth in spring and stunting was not statistically significant. CONCLUSIONS: Stunting was associated with season of birth among children under 3 years old in low-income counties in western China, especially children aged 25 to 36 months, and children born in the summer and autumn were less likely to exhibit stunting than were children born in the winter.
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