Birth seasonality in rural areas of Iran, analysis of 5,536,262 births from 1992 to 2007.

PURPOSE: We conducted this study to investigate birth seasonality in rural parts of Iran. METHODS: In this study, patterns of 5,536,262 live births in rural parts of Iran between 1992 and 2007 were studied. Information about birth numbers, environmental factors, and sociocultural status of participants was obtained from previous works. Visually inspecting the seasonal variation of birth, studying its trend using autocorrelation analysis, examining the trend of birth seasonality using the seasonality coefficient, a newly introduced index, studying correlations between birth seasonality and possible associated factors, and analyzing associations between these variables and birth seasonality using multiple regression model were performed in this study. RESULTS: In this study, we showed birth seasonality in rural parts of Iran, with the highest births in the first two seasons, winter and spring, mostly before the year of 2002. Latitude and mean temperature of districts, wealth status of families, education of women, and mothers' ages were associated with birth seasonality. However, latitude, temperature, and mothers' ages lost their associations after adjusting for sociocultural factors in the regression model. CONCLUSIONS: Birth numbers in rural areas of Iran follow a rhythmic seasonal pattern; however, the ordering of seasons changes in the last years of the study period.