Okay, let's tackle this question. The question is asking by what age a newborn's weight doubles. The options are A, B, C, D, but they aren't provided. However, I remember from pediatric growth patterns that infants typically double their birth weight by around 4 to 6 months of age. Let me verify that.

The core concept here is infant growth patterns, specifically weight gain milestones. Newborns experience rapid growth in the first few months. The mechanism involves normal nutritional intake and metabolic processes. The correct answer would be the time frame when this doubling occurs.

If the options included 4 months, that's likely correct. Common distractors might be 3 months (too early), 1 year (too late), or maybe 2 months (still early). The clinical pearl is that this is a standard growth milestone, and missing it could indicate growth issues. So, the correct answer should be around 4-6 months. Let me structure the explanation accordingly.

**Core Concept**
Newborn weight gain follows a predictable growth curve. The infant's weight doubles by 4–6 months due to rapid postnatal growth driven by adequate nutrition, hormonal regulation (e.g., growth hormone), and metabolic efficiency. This is a key developmental milestone in pediatric assessment.

**Why the Correct Answer is Right**
The newborn typically doubles their birth weight by **5–6 months of age**. This occurs because of consistent caloric intake, efficient nutrient absorption, and growth hormone-mediated anabolic processes. By 6 months, the infant’s gastrointestinal tract matures, allowing optimal digestion of breast milk or formula, supporting this milestone.

**Why Each Wrong Option is Incorrect**
**Option A:** 3 months – Incorrect; most infants do not reach double their birth weight by 3 months, though some may approach it.
**Option B:** 2 months – Incorrect; this is too early; even preterm infants rarely achieve this milestone by 2 months.
**Option D:** 12 months – Incorrect; by 1 year, weight triples, not doubles, due to decelerating growth rates post-6 months.

**Clinical Pearl / High-Yield Fact**
Remember: **"Double by 6, triple by 12"** – a high-yield exam fact for pediatric weight milestones. Failure to double by 6 months may indicate malnutrition, feeding disorders, or underlying metabolic issues requiring investigation.

**Correct Answer: C. 5–6 months**

✓ Correct Answer: A. 6 months