Seasonal variation of birth weight distribution in Morogoro, Tanzania.

The data of 19,783 full term singleton babies were examined to determine the effect of seasonal variation on birth weight. The mean birth weight was found to be 3020 +/- 502 g. Out of these births, 2354 (11.9%) babies weighed less than 2500 g. Birth weight and percentage low birth weight showed variation with season. Mean birth weight was low during the rainy season and high during the dry season, a period immediately after harvest. This observation suggests that mean birth weight varies with season, which in turn determines the level of energy expenditure and food availability. The study has also shown that there is a rapid response of birth weight to changing conditions of food intake and energy expenditure rather than a slow rise or fall in birth weight in response to gradual changes of conditions as is generally believed. Additionally, the study has shown that birth weight does not only respond to the conditions prevailing during the last few months of pregnancy, but also to the conditions existing just before delivery. This observation would have significant implications in food supplementation programmes for pregnant women.