Regional and temporal fluctuations in the incidence of congenital hypothyroidism in Israel.

It is well known that the incidence of congenital hypothyroidism (CH) differs significantly among different parts of the world. Northern Israel has been shown to be an iodine deficient area with a relatively high incidence of CH. This study aimed to compare the incidence of CH between different regions of Israel and to examine the temporal fluctuations of this disease in each region. All 303 primary CH infants born in Israel during the 10-year period between April 1978 and March 1988 were classified by hospital of birth and place of residence. Using these data we calculated the incidence of CH in the different subdistricts and districts of Israel. We also calculated the annual incidence of CH in each district. The incidence of CH in each hospital was compared to the filter paper T4 levels of all newborns born in that hospital during 1993. The incidence of CH decreased gradually from northern to southern Israel. This trend was also observed for thyroid agenesis, but the incidence of ectopic thyroid was highest in central Israel. Dyshormonogenesis (DHG) was on average 3.5 fold more frequent in the Arab compared to the Jewish populations, but did not show any clear geographic pattern. A significantly increased CH incidence in north-central Israel in 1985 was opposed by a low incidence in the South. A clear correlation exists between the incidence of CH in each hospital and the mean newborns' T4 level in that hospital. The incidence of primary CH in general, and of thyroid agenesis and ectopic thyroid specifically, has a clear regional-temporal pattern. Thus, some of the factors causing CH in Israel may be local factors that show local annual fluctuations.