During the active phase of labor the minimum effective dilatation of cervix in primigravida should be at the rate of
**Core Concept**
Active labor in primigravidas is characterized by the cervix dilating at a rate of at least 1 cm per hour. This rate is crucial in distinguishing active labor from latent labor, and it is essential for obstetricians to assess the progress of labor accurately.
**Why the Correct Answer is Right**
The cervix dilates at a rate of 1 cm per hour during active labor in primigravidas. This is because the uterine contractions become more frequent and intense, leading to a faster cervical dilatation. The increase in prostaglandins, such as PGF2α, and the relaxation of the uterine muscle during the active phase of labor facilitate this process. Additionally, the cervical effacement, which is the thinning and shortening of the cervix, also contributes to the faster dilatation.
**Why Each Wrong Option is Incorrect**
**Option A:** 0.5 cm per hour - This rate is too slow to be considered active labor, as it is more characteristic of latent labor.
**Option B:** 1.5 cm per hour - Although this rate is faster than the minimum effective dilatation, it is not the minimum rate required to distinguish active labor from latent labor.
**Option C:** 2 cm per hour - This rate is excessively high and may not be physiologically possible for all primigravidas.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the rate of cervical dilatation can vary significantly among individuals, and a rate of 1 cm per hour is only a minimum benchmark for active labor. Any deviation from this rate should prompt further evaluation and assessment of the labor progress.
**Correct Answer:** C. 1 cm per hour