Strategies behind the establishment of a developmental cohort study in the Tottori City.

BACKGROUND: The Tottori study group, part of the JCS, presides over a community-based cohort study started when subjects-children living in Tottori City-were 5 years old. The social aspects of conducting a cohort study should also be made public, as this information is crucial for conducting community-based cohort studies. METHODS: Documents pertaining to social aspects implemented by the Tottori study group between 2004 and 2008 were arranged chronologically. Information which is crucial for conducting community-based cohort studies were extracted and classified into several categories. RESULTS: Five categories were extracted from the documents: research staff, supporting committee, recruitment, maintenance of motivation and disclosure. Implementation of the social aspects described in maintenance of motivation resulted in fewer subjects dropping out of the study and a re-recruitment rate of approximately 90%. CONCLUSIONS: The following factors are essential for a successful developmental cohort study of children: 1) A birth cohort study should be planned in hospitals with medical staff such as obstetricians and pediatricians; 2) An interdisciplinary group composed of medical or psychological clinicians and researchers with abundant experience in epidemiological study should be included; 3) If possible, an expert or widely known individual in the study's target field should be included as a member of the study staff; 4) For long cohort studies, a researcher with expertise in school education should be included; 5) A support committee should be organized as an external part of the study team.

Live birth prevalence of Down syndrome in Tottori, Japan, 1980-1999.

One hundred sixty-four patients with Down syndrome (DS) were confirmed in Tottori Prefecture, Japan, from 1980 to 1999. The sex ratio of 1.52 (99 males and 65 females) was comparable to that reported in previous studies. The live birth prevalence per 1,000 was 1.52 (95% CI: 1.29-1.75) from 1980 to 1999, with a prevalence of 1.34 (95% CI: 1.05-1.63) recorded between 1980 and 1989, and 1.74 (95% CI: 1.37-2.11) between 1990 and 1999. There was no statistically significant change between these two decades (chi(2)-test). Live birth prevalence in these two decades showed a significant increase (chi(2)-test, P < 0.005) compared with that recorded in 1969-1978 in Tottori Prefecture (0.803, 95% CI: 0.677-0.929). Mean ages of mothers at the birth of a DS patient were 31.0 years in 1980-1989 and 32.4 years in 1990-1999 (t-test, no significant difference). Dispersion analysis on the mean age of mothers at birth for patients born between 1969-1978, 1980-1989, and 1990-1999 showed a significant difference (t-test, P < 0.005), while comparing the mean age of mothers in 1969-1978 to those in 1990-1999 also revealed a significant difference (t-test, P < 0.001). Live birth prevalence has increased due to the rise in fertility rates among older women, although maternal age-specific risk rates remain unchanged. The widespread introduction of induced abortion following prenatal diagnosis decreased live birth prevalence of DS largely in European (and a few Asian) countries after 1990, or kept prevalence steady, despite increasing fertility rates among women aged 30 and over. In contrast, all published studies have reported an increase in live birth prevalence of this syndrome in Japan, probably resulting from the fact that prenatal diagnoses are used only exceptionally in this country (due to the negative attitude toward selection of life in Japanese culture).