The nurse caring for a toddler is diagnosed with congenital hypothyroidism. Which of the following developmental delays should the nurse recognize as the priority concern if the condition is left untreated?

A. Delayed motor skills: Thyroid hormone deficiency can impair muscle tone and coordination, leading to delayed gross and fine motor development. Motor delays are common but may improve with treatment initiation. They are not the most severe long-term consequence if the condition remains untreated. B. Delayed social interactions: Social development may be affected secondary to overall developmental delay, but it is not the primary or most critical impact of untreated congenital hypothyroidism. Social deficits often reflect underlying cognitive impairment rather than isolated thyroid effects. Early hormone replacement can mitigate these concerns. C. Delayed language development: Language delay is frequently observed due to impaired neurologic maturation and slowed cognitive processing. While significant, language skills are influenced by broader cognitive function. Addressing thyroid deficiency early helps prevent long-term speech and language deficits. D. Delayed cognitive abilities: Thyroid hormone is essential for brain development, particularly in early childhood when neuronal growth and myelination are most active. Untreated congenital hypothyroidism can result in permanent intellectual disability. Cognitive impairment represents the most serious and irreversible developmental consequence.