A 14-year-old girl presents with primary amenorrhea and monthly lower abdomen pain. She has good secondary sexual characteristics with axillary and pubic hair. Examination of the external genitalia reveals a bulging bluish membrane. Most appropriate next step in diagnosis:

**Core Concept**
The clinical presentation suggests a condition affecting the female reproductive system, likely related to **obstructive reproductive anomalies**. Primary amenorrhea combined with cyclic abdominal pain and the presence of secondary sexual characteristics points towards an issue with menstrual flow rather than a hormonal imbalance. The bulging bluish membrane is indicative of an **imperforate hymen**, a condition where the hymen completely covers the vaginal entrance, preventing menstrual blood from draining.

**Why the Correct Answer is Right**
Given the symptoms and physical findings, the most appropriate next step would involve confirming the diagnosis of an **imperforate hymen**. This condition leads to **hematocolpos** (accumulation of blood in the vagina) and potentially **hematometra** (accumulation of blood in the uterus), causing the cyclic pain. The presence of good secondary sexual characteristics indicates normal hormonal function, supporting the diagnosis of a mechanical obstruction.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect as it doesn't directly address the likely diagnosis of an imperforate hymen.
**Option B:** Might be considered if there were suspicions of other obstructive anomalies, but the physical exam finding of a bulging bluish membrane is highly suggestive of an imperforate hymen.
**Option D:** Is not relevant to the immediate diagnosis and management of the suspected condition.

**Clinical Pearl / High-Yield Fact**
It's crucial to recognize the signs of an imperforate hymen, as delayed diagnosis can lead to complications such as **endometriosis** due to retrograde menstruation. Immediate relief of the obstruction can prevent these long-term issues.

**Correct Answer:** D. Examination under anesthesia and possible surgical intervention to relieve the obstruction.

✓ Correct Answer: D. Perform an USG