## **Core Concept**
The question tests the understanding of normal growth patterns in newborns, specifically the expected timeline for a newborn to double its birth weight. This is an important milestone in pediatric growth and development.

## **Why the Correct Answer is Right**
A newborn typically doubles its birth weight by around 6 months of age. This growth pattern is a general guideline and can vary slightly among individuals. The rate of growth is rapid during the first few months of life. By 6 months, most infants have doubled their birth weight, which is a significant indicator of healthy growth and adequate nutrition.

## **Why Each Wrong Option is Incorrect**
- **Option A:** By 2 months, a newborn may have increased its weight by 20-30%, but it usually hasn't doubled its birth weight yet. This period is crucial for growth, but doubling typically occurs later.
- **Option B:** By 4 months, some infants might be close to doubling their birth weight, but it's generally a bit early for most to reach this milestone. Growth rates can vary, but 4 months is often too soon.
- **Option D:** By 12 months, most infants have tripled their birth weight, not just doubled. This option is too late for the specific milestone of doubling birth weight.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that by 6 months, a baby's birth weight should approximately double, and by 12 months, it should have tripled. This is a crucial indicator of normal growth and development. Clinicians often use these milestones to assess the health and nutritional status of infants.

## **Correct Answer:** . 6 months.