Which of the following is NOT a characteristic of high-risk gestational diabetes mellitus?

The option that indicates a characteristic that is not typically associated with high-risk gestational diabetes mellitus is the age over 25 years. While age can be a factor in the development of gestational diabetes, being over 25 is often considered a common risk factor rather than one that defines "high risk."

In the context of gestational diabetes, several specific characteristics such as obesity, prior history of GDM, and polycystic ovarian syndrome clearly denote a higher risk for developing the condition. Obesity increases insulin resistance, which is a significant factor in the development of gestational diabetes. A prior history of gestational diabetes indicates that the individual has previously experienced this condition, leading to a markedly increased likelihood of recurrence in subsequent pregnancies. Polycystic ovarian syndrome (PCOS) is also associated with insulin resistance and is recognized as a risk factor for developing gestational diabetes.

Thus, while being over 25 years old is a general risk factor, it does not denote a high-risk status in the same way that the other options do.