## **Core Concept**
The question describes a 5-year-old girl with primary amenorrhea, short stature, and absent secondary sexual characteristics. The presence of a uterus and vagina on ultrasound, along with high levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), suggests a diagnosis related to ovarian dysfunction or failure.

## **Why the Correct Answer is Right**
The clinical presentation and laboratory findings point towards ovarian dysgenesis, most commonly Turner syndrome, which is characterized by short stature, gonadal dysgenesis (leading to high FSH and LH levels), and the presence of a uterus and vagina. Karyotyping is essential to confirm Turner syndrome (45,X) or other chromosomal abnormalities. This step is crucial for confirming the diagnosis and guiding further management.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, it would be incorrect if it did not directly lead to a diagnosis or if it was not relevant to confirming ovarian function or chromosomal abnormalities.
- **Option B:** This option is not provided, but if it suggested another diagnostic step that does not directly assess chromosomal abnormalities or ovarian function, it would be incorrect.
- **Option C:** This option is not provided, but if it proposed a treatment step without a confirmed diagnosis, it would be premature.
- **Option D:** This option is not provided, but if it suggested an incorrect method for confirming the diagnosis, such as not addressing chromosomal analysis, it would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in cases of primary amenorrhea with high FSH levels, Turner syndrome should be a leading consideration, and **karyotyping** is a critical diagnostic step. This condition often presents with short stature and gonadal dysgenesis.

## **Correct Answer:** . Karyotyping