Evolution of Subclinical Hypothyroidism Diagnosed in the First 3 Months of Life in Newborns Living in North Italy: A Retrospective Cohort Study

Background: Subclinical hypothyroidism (SH) management in neonatal age opens important questions. We aimed to describe the evolution over time of subclinical hypothyroidism diagnosed in the first three months of life in a population of full-term neonates. Methods: A single-center longitudinal retrospective cohort study in a tertiary care center was conducted. We recruited 32 subjects with SH diagnosed within the first three months of life. We collected clinical, biochemical, and ultrasound data for every subject at the first examination and every six months until four years of age. Results: A total of 43.8% of subjects showed stimulating thyroid hormone (TSH) levels over the limit of 10 mUI/L and underwent treatment (Group 1). Eleven subjects started therapy at the first visit, while three subjects started it after a period of observation; 15.6% (Group 2A) showed a trend of TSH decrease and were finally discharged from the follow-up, while 40.6% (Group 2B) showed a TSH level slightly increased, changeless over time. Conclusions: We demonstrated that more than half of newborns with hyperthyrotropinemia did not require substitutive therapy showing a positive trend toward normalization or a remaining slight increase compared to normal levels. Moreover, our study suggests the need for a follow-up over time to check the TSH levels course.