**Core Concept**
Vaginal changes in pregnancy are primarily due to increased levels of estrogen, which cause hypertrophy of the vaginal epithelium and increase in vascularity. This leads to a series of changes that can be observed throughout pregnancy.

**Why the Correct Answer is Right**
The vaginal epithelium undergoes significant changes due to the increased estrogen levels, resulting in an increase in the thickness of the vaginal wall. This, in turn, leads to an increase in the vaginal pH, which is usually alkaline in nature. The increased vascularity of the vaginal wall also contributes to the changes observed during pregnancy. These changes are essential for the preparation of the vagina for potential childbirth.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the vaginal changes observed in normal pregnancy. While there may be some mild cervical dilation, it is not a characteristic feature of normal pregnancy.

**Option B:** This option is incorrect as it is a feature of cervical cancer, not normal pregnancy. Cervical cancer can cause abnormal vaginal bleeding and cervical dilation, but this is not a normal finding in pregnancy.

**Option C:** This option is incorrect as it describes a feature of preterm labor, not normal pregnancy. Preterm labor is characterized by cervical dilation and effacement, which can occur before the 37th week of gestation.

**Clinical Pearl / High-Yield Fact**
It's essential to note that while vaginal changes are a normal part of pregnancy, any abnormal vaginal bleeding or discharge should be investigated to rule out any underlying conditions.

**Correct Answer: D. Increased vascularity and hypertrophy of the vaginal epithelium.**