A time-series analysis of the incidence of down's syndrome in West Jerusalem

The age-adjusted monthly incidence of Down's syndrome has been studied in 42,340 births in 1964-1970 in the Jerusalem Perinatal Study. The overall rate was 2.4/1000 total births. There was a highly significant short-term cycle of 6 months with peaks among spring and autumn births in 6 of the 7 years studied that was independent of maternal age and standard of living. There was also a long-term decrease in Down's syndrome incidence, which may be part of a cycle of approximately 10 years. The data support the hypothesis that environmental factors play a major role in the etiology of Down's syndrome.