Clinical Research Directory

Inclusion Criteria: * Male and female patient aged 0 to 9 months * Primary CH diagnosis with elevated TSH and low or normal FT4, requiring treatment with LT4, under either of the following conditions: * Neonates newly diagnosed with primary CH and needing to initiate LT4 therapy, or * Infants previously diagnosed with primary CH and who are already on LT4 therapy for at least 3 weeks; * Provide and comply with the informed consent. Exclusion Criteria: * Preterm neonates with a gestational age \< 37 weeks; * Low birth weight (LBW) or very low birth weight (VLBW) neonates (weight \< 2.5 kg) or VLBW infants (weight \< 1.5 kg); * Neonates in neonatal intensive care units or requiring admission to NICU or neonates/infants hospitalized or requiring hospitalization or in fragile health conditions (e.g. with serious health problems or complications); * Neonates with CH diagnosis \> 4 weeks after delivery; * Diagnosis of primary gastrointestinal disease: * Gastroesophageal reflux requiring medical therapy (beyond thickening of formula or position); * Anatomic defects (e.g. intestinal atresia, malrotation, tracheoesophageal fistula, pyloric stenosis, Hirschsprung's disease, gastroschisis); * Dietary allergy (e.g. cow's milk protein allergy); * Malabsorption related to cystic fibrosis, celiac disease and others; * Necrotizing enterocolitis requiring surgical resection; * Known or suspected adrenal insufficiency (e.g. congenital adrenal hyperplasia, hypopituitarism); * Diagnosis of congenital cardiac disease, cardiac insufficiency or risk for cardiac failure; * Diagnosis of chromosomopathy; * Diagnosis of central hypothyroidism; * Hypersensitivity to glycerol; * Concomitant anticonvulsant medications, liothyronine, combination of LT4 and liothyronine, thyroid extracts and/or chronic or long-term use of systemic glucocorticoids * History of nonadherence with medication or medical visit schedule; or * Any condition for which, participation would not be in the best interest of the patient or that could limit protocol specified assessments.