**Core Concept:**
Vaginal bleeding in a female neonate is a concerning symptom that requires prompt evaluation as it can indicate various pathologies. The most common causes include vaginal bleeding due to vaginal atony, retained products of conception, or genitourinary malformations such as VUR, VSD, or urethral abnormalities.

**Why the Correct Answer is Right:**
The correct answer is "C. Investigate for genitourinary malformations", as vaginal bleeding in a female neonate should trigger a thorough evaluation for underlying genitourinary abnormalities. Retained products of conception (RPOC) are a potential cause, but they are less likely after 4 days of life when the risk of retained placenta decreases.

**Why Each Wrong Option is Incorrect:**
A. "Observe and reassess" is incorrect because vaginal bleeding should prompt investigation rather than observation only.
B. "Consider for vaginal atony" is not the primary approach, as vaginal atony is a less common cause after the first week of life.
D. "Investigate for abdominal pathology" is too broad and does not address the primary concern of genitourinary malformations.

**Clinical Pearl:**
A neonatal genitourinary evaluation should focus on the genital tract, bladder, and urethra. A detailed history and physical examination, including perineal exam and abdominal palpation, are essential. Additional investigations, such as ultrasound, voiding cystourethrogram (VCUG), and cystoscopy, may be required based on the findings during the initial evaluation. Remember that vaginal bleeding in females is a clinical alert, and prompt investigation is crucial to prevent complications and provide appropriate management.