**Core Concept**
The underlying principle being tested is the timing of blood specimen collection for neonatal thyroid screening, which is crucial for detecting congenital hypothyroidism early in life. This screening is based on the measurement of **thyroid-stimulating hormone (TSH)** and/or **thyroxine (T4)** levels in the blood.

**Why the Correct Answer is Right**
The correct timing for obtaining a blood specimen for neonatal thyroid screening is typically between 2 to 5 days of life, but the most commonly recommended time is around **3 to 5 days** after birth. This allows for the detection of congenital hypothyroidism, which is essential for early intervention and prevention of mental retardation and other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too early for accurate screening.
**Option B:** This option might be too late for some screening programs.
**Option D:** This is not a standard option for neonatal thyroid screening timing.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that early detection and treatment of congenital hypothyroidism can significantly improve outcomes, emphasizing the importance of timely neonatal screening.

**Correct Answer:** D. 3 to 5 days of life