Risk of preterm delivery is increased if cervical length is :
**Core Concept**
The risk of preterm delivery is closely associated with cervical length, particularly in pregnant women at high risk of preterm labor. A normal cervical length is crucial in maintaining fetal well-being and preventing preterm birth.
**Why the Correct Answer is Right**
A short cervical length, typically defined as less than 25 mm, is a significant predictor of preterm labor and delivery. This is because a shortened cervix is more susceptible to dilation and effacement, which can lead to preterm birth. The mechanism behind this is thought to be related to the increased expression of matrix metalloproteinases (MMPs) and other proteolytic enzymes that break down the cervical extracellular matrix, leading to cervical shortening.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a cervical length of 35 mm is actually considered within the normal range, and a longer cervix is not a risk factor for preterm delivery.
**Option B:** This option is incorrect because a cervical length of 10 mm is significantly shorter than the normal range and is indeed a risk factor for preterm delivery, but it is not the correct answer as it is not the option that is being compared to.
**Option C:** This option is incorrect because a cervical length of 30 mm is within the normal range, and a longer cervix is not typically associated with an increased risk of preterm delivery.
**Clinical Pearl / High-Yield Fact**
It is essential for healthcare providers to measure cervical length in high-risk pregnant women to assess the risk of preterm delivery. A cervical length of less than 25 mm is a significant predictor of preterm labor and delivery.
**Correct Answer: C. A cervical length of 25 mm is considered the threshold for increased risk of preterm delivery.**