**Core Concept**
Postpartum vesicovaginal fistula (VVF) is an abnormal fistulous connection between the bladder and vagina, often caused by prolonged obstructed labor. The optimal time for surgical repair is crucial to minimize complications and ensure successful outcomes.

**Why the Correct Answer is Right**
The best time to repair postpartum VVF is after the patient has completed childbearing. This is because the tissues involved in the fistula repair are more favorable for healing when not under the stress of pregnancy. Additionally, waiting until after childbearing reduces the risk of recurrence and improves the overall success rate of the surgery. The optimal time for repair is usually 6-12 months after the last pregnancy, allowing for adequate tissue healing and minimizing the risk of complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Immediate repair after diagnosis is incorrect because the tissues may not be fully healed, leading to a higher risk of complications and recurrence.
**Option B:** Repair during pregnancy is incorrect because the increased intra-abdominal pressure and hormonal changes can compromise the surgical outcome and increase the risk of recurrence.
**Option C:** Repair within 3-6 months after diagnosis is incorrect because the tissues may not have fully healed, and the patient may still be under the stress of recent childbirth.

**Clinical Pearl / High-Yield Fact**
It is essential to counsel patients with postpartum VVF about the importance of waiting until after childbearing before undergoing surgical repair to ensure the best possible outcomes.

**Correct Answer: D.**