**Core Concept**
Braxton Hicks contractions are a type of uterine contraction that occurs during pregnancy, typically starting in the second trimester. These contractions are characterized by intermittent, painless, and non-rhythmic uterine tightening, which are distinct from true labor contractions.

**Why the Correct Answer is Right**
Braxton Hicks contractions are a physiological phenomenon that helps prepare the uterus for labor. They are thought to be triggered by hormonal changes, particularly an increase in progesterone levels, which cause the uterine smooth muscle to contract. These contractions are also influenced by the growing uterus, which can cause the smooth muscle to become overactive and contract more frequently. The painless nature of Braxton Hicks contractions is due to the fact that they do not stimulate the pain-sensitive nerve endings in the uterus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Braxton Hicks contractions are not typically associated with cervical dilation or effacement, which are characteristic of true labor.
**Option B:** This option is incorrect because Braxton Hicks contractions do not typically increase in frequency or intensity as the pregnancy advances, unlike true labor contractions.
**Option C:** This option is incorrect because Braxton Hicks contractions are not a sign of placental abruption or other complications that require immediate medical attention.

**Clinical Pearl / High-Yield Fact**
To differentiate Braxton Hicks contractions from true labor contractions, look for the presence of regular, increasing, and intense uterine contractions, as well as cervical dilation or effacement.

**Correct Answer:** A. Braxton Hicks contractions.