To examine the difference in abnormal conception by region and generation and its possible causes in the town of Tsunagi, which experienced intensive methylmercury-pollution during the 1950s and 1960s, reproductive histories of 109 women in 3 coastal willages and 64 controls in 5 inland willages were obtained by visit-and interview-study in 1991. There were about 290 married women in respective regions. The subjects were divided into 4 age groups to form 10-year-birth cohorts from 1915 to 1954.
The rate of sterility and those who had never become pregnant after marriage, did not differ between coastal (7.3%) and inland women (6.3%). The younger the birth cohort, the smaller the total number of conceptions. The rate of abnormal conception, i. e., abnormal conception (abortion+stillbirth) per normal conceptions (total number of conceptions-number of artificial abortions), in the coastal women tended to increase after the 1960s with its peak (19%) in 1965-70. The rate in the inland women was already as high as 15% in 1945-50, and was constantly above 10% afterwards. However, it did not differ between the two groups during 1950-1970, when severe methylmercury-pollution occurred in the area.
Breakdown of the abnormal conceptions in the inland women showed 4 stillbirths and 19 abortions, among the latter of which 16 were related to climbing up and down the hills to fetch water, hard agricultural work and agitation. The abnormal conceptions in the coastal women showed 3 stillbirths and 19 abortions. Sixteen of the latter were not related to any specific physical causes.
