Incidence of primary congenital hypothyroidism and relationship between diagnostic categories and associated malformations.

Purpose: The incidence of primary congenital hypothyroidism (CH) has grown progressively and literature data indicate an association between CH and congenital malformations. The purpose of this study is to establish the current incidence of CH in the Italian Region of Piedmont and verify the relationship between CH diagnostic categories and associated malformations.

Methods: The biochemical and clinical data of 105 newborns with CH diagnosed in the period January 2014 to December 2019 were analyzed.

Results: The incidence of CH in the Italian Piedmont region in the 2014-2019 period increased to 1:1090. Thyroid dysgenesis was responsible for 47.6% (50/105) of all cases, with agenesis in 14.3% (15/105), while ectopia and hypoplasia in 23.8% (25/105) and 9.5% (10/105) of the cases, respectively; dyshormonogenesis defects were found in 52.4% (55/105) of cases. Congenital extra-thyroid anomalies were identified in 33/105 (31.4%) of newborns with CH and mainly involve the cardiac system (17/85, 16.1%), urogenital tract (7/85, 6.7%), gastrointestinal tract (5/105, 4.8%), and the musculoskeletal system (5/105, 4.8%). The highest rate of malformations was observed in patients with thyroid agenesis and dyshormonogenesis, respectively, in 53.5% and 36.4% of cases, while in the presence of thyroid ectopia and hypoplasia, the rate was 12% and 20%, respectively, (p = 0.03).

Conclusion: In the Italian region of Piedmont, the incidence of primary CH has been increased over time, with a variation in the percentage of the different forms of CH. Congenital malformations, especially affecting the cardiovascular, urogenital, gastrointestinal, and musculoskeletal systems, seem to be mainly associated with thyroid agenesis or defects in hormonogenesis.