Background and purpose: Congenital hypothyroidism (CH) is one of the most common preventable causes of mental disabilities. The present study was conducted to determine the prevalence of permanent and transient congenital hypothyroidism in Mazandaran province, Iran.
Materials and methods: This retrospective descriptive survey was done based on medical records of children with primary diagnosis of congenital hypothyroidism between 2006 and 2014.
Results: Until March 2012, 176250 infants were screened for congenital hypothyroidism of whom 389 were diagnosed with the disease (1 per 453 births). Among these cases, 169 had permanent CH (1 per 1043 births) and 220 had transient CH (1 per 801 births).  Until 2014 a total of 269088 newborns was screened by which 548 case of primary congenital hypothyroidism were diagnosed (1 per 491 births) but their definitive diagnosis are not available until the next three years. The girl/boy ratio in permanent CH group was higher than that in transient CH (P=0.08).
Conclusion: This study showed a high prevalence of transient and permanent hypothyroidism in Mazandaran, but transient CH was found to be more prevalent. Therefore, the factors affecting the development of transient CH and its higher incidence among male infants in Mazandaran province are required to be specifically investigated in future researches.