**Core Concept**
Ectopic pregnancy occurs when a fertilized ovum implants outside the uterine cavity, typically in the fallopian tube. The highest risk is associated with anatomical abnormalities or disruptions that obstruct normal ovum transport or increase the likelihood of implantation outside the uterus.

**Why the Correct Answer is Right**
The correct answer is associated with **salpingectomy**, or the surgical removal of a fallopian tube. This procedure significantly increases the risk of ectopic pregnancy because it eliminates the normal pathway for the ovum to travel to the uterus. The remaining tube may be compromised, or the ovum may implant in the remaining tube or in the abdominal cavity.

**Why Each Wrong Option is Incorrect**
**Option A:** _Tubal ligation_, while increasing the risk of ectopic pregnancy, does not pose the highest risk compared to salpingectomy. Tubal ligation involves blocking the fallopian tubes, but the tubes are not removed, and the risk of ectopic pregnancy is still lower than with salpingectomy.

**Option B:** _Pelvic inflammatory disease (PID)_ increases the risk of ectopic pregnancy, but it is not the highest risk factor. PID can cause scarring and damage to the fallopian tubes, but the risk of ectopic pregnancy is still lower than with salpingectomy.

**Option C:** _In vitro fertilization (IVF)_ does not increase the risk of ectopic pregnancy; if anything, it may decrease the risk because the embryo is transferred directly to the uterus.

**Clinical Pearl / High-Yield Fact**
When assessing a patient with a history of ectopic pregnancy, a thorough obstetric and gynecological history, including any previous surgeries, is essential in identifying high-risk factors.

**Correct Answer:** C. Salpingectomy.