**Core Concept**
The patient's presentation is suggestive of a molar pregnancy, which is a type of gestational trophoblastic disease characterized by the abnormal growth of trophoblastic cells in the uterus, leading to the formation of a mass of cystic, avascular structures.

**Why the Correct Answer is Right**
The clinical presentation, including uterine bleeding, passage of watery fluid and tissue, and a uterus larger than expected for gestational age, is consistent with a molar pregnancy. The presence of cystic, avascular, grapelike structures that do not penetrate the uterine wall further supports this diagnosis. These structures are typically composed of hydropic villi, which are avascular and do not contain a fetus.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a normal pregnancy would not typically present with uterine bleeding and a uterus larger than expected for gestational age.
* **Option B:** This option is incorrect because a ectopic pregnancy would not present with a uterus larger than expected for gestational age, and the ultrasound findings described would not be consistent with an ectopic pregnancy.
* **Option C:** This option is incorrect because a missed abortion would typically present with a non-viable fetus, which is not consistent with the ultrasound findings described.
* **Option D:** This option is incorrect because a placental abruption would typically present with severe abdominal pain and vaginal bleeding, which is not consistent with the patient's presentation.

**Clinical Pearl / High-Yield Fact**
A key feature of a molar pregnancy is the presence of beta-hCG levels that are higher than expected for gestational age, which can be used to differentiate it from a normal pregnancy.

**Correct Answer: D. Molar pregnancy**