## **Core Concept**
O'Sullivan & Mahan criteria are used in the diagnosis of **Gestational Diabetes Mellitus (GDM)**. These criteria help in identifying pregnant women at risk of developing glucose metabolism disorders during pregnancy.

## **Why the Correct Answer is Right**
The O'Sullivan & Mahan criteria, established in 1964, are significant because they were among the first to screen for gestational diabetes. They proposed a 1-hour glucose challenge test (GCT) followed by a diagnostic 3-hour oral glucose tolerance test (OGTT) if the initial test was abnormal. The criteria specifically look for glucose levels at various intervals post-glucose ingestion to diagnose GDM. This method has been foundational in managing and diagnosing GDM.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while various diagnostic criteria exist for diabetes and glucose intolerance, O'Sullivan & Mahan specifically relate to gestational diabetes, not general diabetes diagnosis.
- **Option B:** This option is incorrect as there are other criteria for diagnosing diabetes in non-pregnant individuals, but O'Sullivan & Mahan criteria are pregnancy-specific.
- **Option C:** Although not directly provided, any other option not related to gestational diabetes or specific diagnostic criteria for GDM would be incorrect.
- **Option D:** Similarly, without specifics, any option not aligned with GDM diagnosis or O'Sullivan & Mahan criteria would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **Carpenter & Coustan** and **National Diabetes Data Group (NDDG)** criteria later modified and updated the O'Sullivan & Mahan criteria. However, O'Sullivan & Mahan remain historically significant and relevant in the context of gestational diabetes screening.

## **Correct Answer:** C. Gestational Diabetes Mellitus.