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

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.