**Core Concept**
Vaginal bleeding in neonates is a common condition that requires prompt evaluation and diagnosis. The underlying cause is often related to the sudden withdrawal of maternal hormones, particularly estrogen, after birth.

**Why the Correct Answer is Right**
Hormonal withdrawal is the most common cause of vaginal bleeding in neonates. This occurs due to the abrupt cessation of maternal estrogen levels after birth, leading to atrophy of the vaginal mucosa and subsequent bleeding. The vaginal mucosa in neonates is highly sensitive to changes in estrogen levels, making them prone to bleeding when exposed to the sudden drop in hormone levels. This condition is often referred to as vaginal withdrawal bleeding.

**Why Each Wrong Option is Incorrect**
**Option A:** Sarcoma botryoides is a rare and malignant tumor that affects the vagina and cervix in infants and young children. It is characterized by a mass of polypoid tissue and is not a common cause of vaginal bleeding in neonates.

**Option B:** Trauma of delivery is a potential cause of vaginal bleeding in neonates, but it is not the most common cause. Trauma can occur during the birth process, but it is often associated with other complications such as bruising or lacerations.

**Option D:** Viral infection is a rare cause of vaginal bleeding in neonates. While certain viral infections can cause genital lesions or ulcers, they are not a common cause of vaginal bleeding in this age group.

**Clinical Pearl / High-Yield Fact**
Neonatal vaginal bleeding is often self-limiting and resolves spontaneously within a few days. However, it is essential to evaluate the cause of bleeding to rule out any underlying conditions that may require medical attention.

**✓ Correct Answer: C. Hormonal withdrawal**