Delaying thyroid hormone therapy for neonatal congenital hypothyroidism by 8 days can result in which outcome?

• A. No effect on IQ
• B. Weight gain
• C. Decrease in IQ
• D. Increased IQ

Answer: (C)

The key idea is that newborn brain development depends on thyroid hormone, and there’s a critical window in the first weeks of life when this hormone is essential for cognitive maturation. When congenital hypothyroidism is not treated promptly, the brain doesn’t receive enough thyroid hormone during that window, leading to irreversible changes in neural development. Delaying thyroid hormone therapy by about 8 days can result in cognitive impairment, manifesting as a decreased IQ later on. Starting levothyroxine as early as possible helps minimize these neurodevelopmental deficits. Weight or growth effects may occur, but they do not capture the primary long-term consequence of delayed treatment, which is reduced cognitive outcomes.