Seasonal variation of births in rural southwestern Nigeria.

A total of 12 708 live births registered between 1965 and 1975 in Igbo Ora, a rural area in southwestern Nigeria, were examined for seasonal variation using trigonometric regression analysis. The monthly number of registered births showed a significant seasonal pattern with a peak in May and corresponding minima in November. The extent of the seasonal variation above and below the annual mean was about 7%. There has been no significant shift in both the month of peak occurrence and the magnitude of the variation within the 11-year period of study. It is thought that the observed seasonal pattern may be related to climatic factors as well as sociocultural patterns of life associated with cyclical farming activities characteristic of a predominantly agricultural community.