**Core Concept:** A primigravida (first pregnant woman) at term is nearing the end of pregnancy, typically 37 weeks or more. The sure signs of labor indicate the active first stage of labor, where the cervix dilates and effaces to prepare for birth.

**Why the Correct Answer is Right:** The correct answer, **Option C: Active phase of the first stage of labor**, is defined as the period when cervical changes become irreversible and progress. In this phase, the cervix dilates from 3-4 cm to 10 cm, and effaces (thinning and shortening) significantly. The contractions become stronger, more frequent, and last longer.

**Why Each Wrong Option is Incorrect:**

A. **Option A: Contractions becoming stronger:** While contraction strength is a feature of labor, it is not specific enough to be considered a sure sign of labor. Contractions can also be intense in pregnancy, especially towards the end due to changes in hormone levels and uterine preparation.

B. **Option B: Vaginal discharge:** While discharge is a common sign during labor, it can also occur during other pregnancy stages (e.g., ruptured membranes, effacement). Therefore, discharge alone is not a sure sign of labor.

D. **Option D: Rupture of membranes (ROM):** While rupture of membranes (ROM) is a significant event during labor, it can occur in the second stage of labor (when the cervix ripens and dilates) or even prematurely due to preterm labor.

**Clinical Pearl:** A sure sign of labor is the combination of the active phase of the first stage of labor (Option C) along with the second stage of labor (contraction strength, cervical changes, and ROM). This combination increases the likelihood of labor and helps differentiate it from other pregnancy symptoms.