**Core Concept**
Childbirth trauma leading to urine incontinence is a common condition known as stress urinary incontinence (SUI), which occurs due to the weakening or stretching of the pelvic floor muscles and supporting tissues during childbirth. The condition is more prevalent in women with a history of vaginal delivery, especially those with instrumental delivery or prolonged second stage of labor.

**Why the Correct Answer is Right**
The least affected group is likely to be women who have undergone a cesarean section (C-section), as this type of delivery does not involve the same level of vaginal trauma and pelvic floor muscle stretching as vaginal delivery. A C-section is considered a safer option for women who are at high risk of developing SUI, especially those with a history of pelvic floor dysfunction or previous pelvic surgery.

**Why Each Wrong Option is Incorrect**
* **Option A:** Women with a history of multiple vaginal deliveries are at higher risk of developing SUI due to increased pelvic floor muscle stretching and weakening. Therefore, this option is incorrect.
* **Option B:** Women with a history of instrumental delivery (e.g., forceps or vacuum extraction) are at higher risk of developing SUI due to increased pelvic floor muscle trauma. Therefore, this option is incorrect.
* **Option C:** Women with a history of prolonged second stage of labor are at higher risk of developing SUI due to increased pelvic floor muscle fatigue and stretching. Therefore, this option is incorrect.

**Clinical Pearl / High-Yield Fact**
A mnemonic to remember the risk factors for SUI is "F.I.T." - Forceps or instrumental delivery, Instrumentation of the perineum, and Traction on the pelvic floor muscles.

**Correct Answer: C**. Women who have undergone a cesarean section are least affected by childbirth trauma leading to urine incontinence.