**Core Concept**
Per rectal palpation of the uterus is a technique used to assess the size, shape, and consistency of the uterus through a digital examination via the rectum. This method is particularly useful in cases where a vaginal examination is not feasible or desirable.

**Why the Correct Answer is Right**
In virgins, per rectal palpation is the preferred method for assessing the uterus due to the lack of vaginal access. This technique allows for the evaluation of the uterine size and consistency without the need for a vaginal examination, which would be uncomfortable or impossible for a virgin patient. The examiner can feel the uterine fundus, cervix, and body through the rectal wall, providing valuable information about the uterine size, shape, and any abnormalities.

**Why Each Wrong Option is Incorrect**
**Option A:** Primigravida patients typically undergo a routine vaginal examination as part of their antenatal care, making per rectal palpation unnecessary.
**Option C:** Grand multiparas have a larger uterine cavity due to repeated pregnancies, and a vaginal examination is usually feasible and necessary for their care.
**Option D:** In cases of placenta previa, a vaginal examination is contraindicated due to the risk of bleeding, and per rectal palpation may not provide sufficient information about the placental location.

**Clinical Pearl / High-Yield Fact**
Performing per rectal palpation in virgins is a classic example of adapting examination techniques to individual patient needs and circumstances, demonstrating a key aspect of bedside manner and clinical judgment.

**✓ Correct Answer: B. Virgins**