**Core Concept:**
Cervical incompetence is a condition characterized by an incompetent cervix, which leads to premature rupture of membranes and preterm labor. Hegar's size dilators are used to assess the cervical length and evaluate cervical ripening in pregnant women.

**Why the Correct Answer is Right:**
Hegar's size dilators are used for cervical evaluation during pregnancy. They are graduated dilators that range in size from 1 to 14. In the context of diagnosing cervical incompetence, the correct answer is:

**Correct Answer: Option C (14)**

**Why Each Wrong Option is Incorrect:**
A. 6 - This size is too small and may not accurately assess the cervical length and ripening.
B. 8 - This size is too large, and using it may cause cervical dilation and interfere with the assessment of cervical competence.
D. 12 - This size is also too large and may cause cervical dilation, making an accurate assessment of cervical competence difficult.

**Why Each Wrong Option is Incorrect:**
A. 6 - This size is too small and may not accurately assess the cervical length and ripening.
B. 8 - This size is too large, and using it may cause cervical dilation and interfere with the assessment of cervical competence.
D. 12 - This size is also too large and may cause cervical dilation, making an accurate assessment of cervical competence difficult.

**Clinical Pearl:**
In clinical practice, cervical dilation assessment is crucial for identifying women at risk of premature labor. Hegar's size dilators can be used to evaluate cervical length and assess cervical ripening. Correctly identifying the appropriate size dilator is essential for accurate evaluation. A dilator size of 14 is suitable for cervical evaluation in the second half of pregnancy.