## Core Concept
A molar pregnancy, also known as hydatidiform mole, is an abnormal pregnancy characterized by the abnormal growth of trophoblasts, the cells that normally develop into the placenta. There are two types of molar pregnancies: complete and partial. The question focuses on the features of a partial mole.

## Why the Correct Answer is Right
Partial moles typically present with a triploid karyotype (69,XXX or 69,XXY), contain fetal tissue, and have a lesser degree of trophoblastic hyperplasia and hydropic villi change compared to complete moles. They are less likely to cause severe symptoms and have a lower risk of progressing to gestational trophoblastic neoplasia.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, partial moles are associated with a triploid karyotype and may contain fetal parts, which makes this option potentially correct regarding features of a partial mole, but without the actual option details, we proceed conceptually.
- **Option B:** If this option describes a feature commonly seen in partial moles, such as less severe trophoblastic hyperplasia, it would be incorrect to label it as an exception.
- **Option C:** Similarly, if this option aligns with known characteristics of partial moles, such as the presence of fetal tissue, it wouldn't be the correct answer to the question about exceptions.
- **Option D:** If this option describes a feature more characteristic of complete moles, such as a diploid karyotype (46,XX), severe trophoblastic hyperplasia, or the absence of fetal tissue, it would be the correct exception.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that partial moles often have a lower risk of malignant transformation compared to complete moles but still require follow-up. The presence of fetal parts in a partial mole can sometimes lead to a delay in diagnosis.

## Correct Answer: D.