Introduction: Subclinical hypothyroidism (SH), or hyperthyrotropinemia, is an asymptomatic condition defined by elevated serum thyroid-stimulating hormone (TSH) levels and normal free thyroxine (FT4) levels. It can be detected in newborns or children, but there is no consensus regarding treatment criteria since FT4 levels often remain normal. [MOU1.1] Materials and methods: We included 116 participants, including infants and children up to 3 years old with subclinical hypothyroidism, born to mothers with autoimmune thyroiditis and those with Down Syndrome. Kaplan-Meier survival analysis determined the median time for TSH normalisation. Cox Proportional Hazards Re-gression was used to explore associated prognostic factors. Results: During the study, 98% of the 116 patients with subclinical hypothyroidism experienced normalisation of their TSH levels, with a median time of 4.0 weeks. Patients who were born term at birth, appropriate for gestational age (AGA), and birth weight of ≥2.5 kg; median (95 % CI):[4 (3.3,4.6)],[4 (3.3,4.6)] [4 (3.3,4.6)] and had a median time of TSH normalisation earlier compared to patients who were born preterm; [12 (0.0,27.1)], small for gestational age (SGA); [8 (4.7,11.2)] and birth weight of < 2.5kg; [8 (1.1,14.8)]. Preterm gestation was identified as a significant predictor for TSH level normalisation with an adjusted HR(95%CI): 0.389(0.2, 0.75), (p=0.005) from multiple Cox regression analysis. [MOU2.1]Conclusion: This study shows that premature patients have a 61.1% lower chance of reaching normal TSH levels, underscoring the signifi-cant challenges they encounter in achieving hormonal balance.