**Core Concept**
Hematuria during labor is a clinical sign that requires prompt recognition and management due to its association with potential complications. In the context of a previous uterine scar, hematuria may indicate an impending rupture of the scar, which is a life-threatening condition.

**Why the Correct Answer is Right**
Hematuria during labor in a woman with a previous uterine scar is often a sign of impending rupture of the scar. This occurs when the scar tissue weakens and fails to support the growing uterus, leading to a potential rupture. The increased intra-abdominal pressure during labor can cause the scar to tear, resulting in severe bleeding and potentially life-threatening consequences. The presence of hematuria in this scenario is a warning sign that requires immediate medical attention.

**Why Each Wrong Option is Incorrect**
**Option B:** Urethral trauma typically presents with pain, swelling, and difficulty urinating, rather than hematuria alone.

**Option C:** Prolonged labor is a risk factor for several complications, but it is not directly associated with hematuria in the context of a previous uterine scar.

**Option D:** Sepsis can cause hematuria, but it is not the primary cause in this specific scenario, and the presence of sepsis would likely be accompanied by other symptoms such as fever and leukocytosis.

**Clinical Pearl / High-Yield Fact**
In a woman with a previous uterine scar, hematuria during labor is a red flag symptom that requires immediate evaluation and management to prevent a potential rupture of the scar. Remember the acronym "PAIN" to associate with scar rupture: Pain, Abdominal tenderness, Incontinence, and Nausea.

**✓ Correct Answer: A. Impending rupture of scar**