**Question:** Following vasectomy, which of the following is true regarding semen analysis?

**Core Concept:** Vasectomy is a sterilization procedure in which the vas deferens are cut and ligated, preventing sperm from reaching the ejaculate. Semen analysis is a test to evaluate the composition of semen and assess male fertility.

**Why the Correct Answer is Right:**

Correct Answer: B. Oligospermia

After a successful vasectomy, the semen analysis typically shows a decrease in semen volume, concentration, and motility due to the absence of sperm in the ejaculate. This condition is known as oligospermia, which refers to having fewer than 15 million sperm per milliliter of semen. This change in semen analysis results is a direct consequence of the vas deferens being obstructed, preventing sperm from being transported to the ejaculate.

**Why Each Wrong Option is Incorrect:**

Option A (azoospermia):
Azoospermia is the absence of sperm in the ejaculate, but it occurs due to factors such as obstructive (e.g., vasectomy) or non-obstructive (e.g., epididymitis, varicocele) causes. Since option A is incorrect due to non-obstructive causes, it is not related to a vasectomy.

Option C (hypospermia):
Hypospermia refers to a decrease in semen volume, but it does not encompass the reduced sperm concentration seen after a vasectomy. Moreover, it does not account for the altered motility and other parameters of semen analysis.

Option D (oligoasthenozoospermia):
Oligoasthenozoospermia describes a combination of reduced sperm count and poor sperm motility, but it does not specifically address the reduced sperm concentration resulting from a vasectomy. Additionally, it does not address the altered semen volume and morphology that might be observed after the procedure.

**Clinical Pearl:**

Vasectomy is a common and effective male sterilization method with a success rate of around 99%. Understanding the changes in semen analysis following a vasectomy helps in counseling patients regarding their fertility potential and interpreting the results of fertility assessments after sterilization procedures.