Seasonality of births and birthweights in Tanzania.

Seasonal patterns of birthrates and birthweights have been compiled from the delivery records of 11 rural hospitals and compared with each other and with the local rainfall pattern by means of lagged regression analysis. While mean birthweight is lower in high rainfall areas, both magnitude and predictability of seasonal birthweight variations are greater in low rainfall areas. Such differences are attributed to different combinations of infection rates, dietary intake and reliability of food supply. Seasonal variations in birthrate were found to occur independently from those of birthweight. Birth seasonality was found to be prominent only in areas with holoendemic malaria and is attributed to a seasonal depression of fecundity mainly due to malaria infection.