**Core Concept**
The softening of the cervix in early pregnancy is a significant clinical sign used in obstetrics to confirm the presence of a gestational sac. This phenomenon is a result of the increased vascularity and the relaxation of the cervical stroma as the pregnancy advances.

**Why the Correct Answer is Right**
The softening of the cervix is primarily due to the increased blood flow and the relaxation of the cervical stroma. As the pregnancy progresses, the cervix becomes more vascular, and the cervical stroma becomes more relaxed, leading to a softer consistency. This change is often palpable during a bimanual examination. The softening of the cervix is one of the earliest signs of pregnancy and is often used in conjunction with other clinical signs, such as uterine enlargement and fetal heart sounds, to confirm the presence of a viable pregnancy.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a recognized clinical sign associated with early pregnancy. While the cervix may undergo changes during pregnancy, softening is the specific term used to describe this phenomenon.
* **Option B:** The Hegar sign refers to the hardening of the uterine isthmus, which is a different clinical sign from the softening of the cervix.
* **Option C:** The Goodell sign refers to the change in the cervical os from a firm, closed os to a soft, open os, which is a different clinical sign from the softening of the cervix.

**Clinical Pearl / High-Yield Fact**
The softening of the cervix is a specific clinical sign that should be distinguished from other changes in the cervix, such as the Hegar sign and the Goodell sign. A healthcare provider should be able to accurately identify and describe this sign in order to confirm the presence of a viable pregnancy.

**Correct Answer:** C. Goodell sign