Abstract
BACKGROUND: Thyroid absorption of iodine could be encumbered by nitrate drinking water when it is transported to the fetal thyroid gland. Therefore, nitrate potentially causes congenital hypothyroidism (CH) due to thyroid dysfunction. In this study, we have not only aimed at spatial determination of CH distribution and nitrate concentration (NC) existing in drinking water, but also we intended to evaluate the probable impact of nitrate on CH incidence. METHODS: Annual average of nitrate in drinking-water as well as number of CH infants diagnosed through the screening program were applied to determine the incidence ratio of the disease for each town (from 2010 to 2013). Afterward, Arc GIS 9.3 was used to draw choropleth maps with quantile classification. Data were entered into SPSS 16.0 and Excel 2010 software. Finally, linear regression was applied for data analysis. RESULTS: The incidence rate of CH (considering transient and permanent cases) was about one in every 413 births. Khansar, Golpaygan, Naein, and Ardestan had the highest incidence rate of CH respectively. On the other hand, Tiran, Dehaghan, Khansar, and Fereydan had the highest level of nitrate drinking water. There was a strong relationship between the NC and incidence of CH in Khansar; however, this relationship was not significant (P = 0.392) in Isfahan province. CONCLUSIONS: Since there was not a significant relationship between NC in drinking-water and incidence of CH through linear regression analysis, more studies should be implemented to confirm or refute our observations.