**Core Concept**
Stress incontinence is a type of urinary incontinence characterized by the involuntary leakage of urine during physical activities that increase abdominal pressure, such as coughing, sneezing, or lifting. It is often associated with weakened pelvic floor muscles, particularly the urethral sphincter.

**Why the Correct Answer is Right**
Stress incontinence occurs when the urethral sphincter is unable to maintain its closure pressure, allowing urine to leak out. This is often due to decreased urethral sphincter muscle strength, which can be caused by childbirth, aging, or neurological disorders. The urethral sphincter is controlled by the pudendal nerve, which innervates the external urethral sphincter muscle.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true. Stress incontinence is indeed often associated with weakened pelvic floor muscles.
**Option B:** This statement is also true. Stress incontinence can be caused by childbirth, particularly vaginal delivery.
**Option C:** This statement is true. Stress incontinence is more common in women than men, largely due to the differences in pelvic floor anatomy and childbirth.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that stress incontinence is often associated with a weak urethral sphincter, which can be treated with pelvic floor exercises (Kegel exercises) or surgery to repair the sphincter.

**Correct Answer: D.**