A comparison of seasonal variation in birthweights between rural Zaire and Ontario

Abstract

We studied the birthweights in a rural area in Zaire over a ten-year period and found a significant seasonal variation. Also, we reviewed the birthweights in two areas of Ontario over a five-year period. One area was in an Ontario Metropolitan hospital doing more than 2000 deliveries per year. The other was in a rural area in southwestern Ontario doing about 500 deliveries per year. No statistically significant seasonal variation in birthweight was found in Ontario. The seasonal variation in Zaire was associated with change in expenditure of energy by the pregnant women, variation in food availability, and malaria.

PIP: A review of the birthweights of 8815 rural Zairian infants born in 1972- 81 revealed significant seasonal variation. The data were collected in an agricultural community where the rainy season peaks in December and drought peaks in July and August. Food availability is greatest in the December-June period. The average birthweight in this population was 2720 grams, with a low of 2610 grams in November and a high of 2806 grams in June. For comparison purposes, birthweights in an urban and rural area of Ontario, Canada, in 1979-83 were reviewed as well. The average birthweight is significantly lower in the metropolitan sample (3258 grams) than the rural sample (3419 grams), but there was no seasonal variation noted in either study site. The findings suggest that, in agricultural societies, there is a strong association between birthweight and seasonality through the impact of variable food intake. Higher birthweights are recorded when the last trimester of pregnancy (when fetal growth is greatest) coincides with months of high food availability and low physical exertion on the part of pregnant women. In this study, birthweights were highest at the peak of the dry season, when harvesting had already taken place, food availability was high, and heavy physical labor was at a minimum. Increasing the food availability during periods of heavy rainfall through special agricultural programs is recommended to reduce the incidence of low birthweight in rural populations.