**Core Concept**
Cesarean scar pregnancy (CSP) is a rare but potentially life-threatening condition where a pregnancy implants in the scar tissue of a previous cesarean delivery. Sonographic evaluation is crucial for diagnosing CSP, and several criteria have been established to help differentiate it from a normal intrauterine pregnancy or an ectopic pregnancy.

**Why the Correct Answer is Right**
The correct answer will not be one of the established sonographic criteria for diagnosing cesarean scar pregnancy. Typically, the following criteria are used:

* A gestational sac located in the lower uterine segment
* A myometrial thickness of less than 3.5 mm
* An empty uterine cavity
* A lack of a clear interface between the gestational sac and the uterine wall
* An abnormal or absent uterine artery Doppler waveform

**Why Each Wrong Option is Incorrect**
**Option A:** A gestational sac located in the lower uterine segment is actually a criterion for CSP, not a criterion that is not used.

**Option B:** Myometrial thickness of less than 3.5 mm is indeed one of the criteria for CSP.

**Option C:** An empty uterine cavity is another criterion that is used to diagnose CSP.

**Option D:** This option is not provided, but for the sake of explanation, if Option D were a criterion for CSP, it would be incorrect because the question asks for a criterion that is NOT used.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient for CSP, it's essential to carefully assess the uterine cavity and look for the characteristic sonographic features mentioned above. A high index of suspicion and prompt diagnosis are crucial to prevent complications.

**Correct Answer: D.**