**Core Concept**
Menorrhagia is a gynecological condition characterized by excessive menstrual bleeding, which can lead to significant morbidity and impact a woman's quality of life. The definition of menorrhagia is crucial in clinical practice, as it guides the evaluation and management of patients with abnormal uterine bleeding.

**Why the Correct Answer is Right**
Menorrhagia is typically defined as blood loss per vagina exceeding 80 mL per menstrual cycle. This threshold is based on studies that have shown that blood loss greater than 80 mL is associated with anemia, iron deficiency, and other complications. The menstrual blood loss is usually measured over a 7-day period, and the average daily blood loss is calculated to determine the total menstrual blood loss.

**Why Each Wrong Option is Incorrect**
**Option A:** Menorrhagia is not defined by blood loss exceeding 40 mL, as this threshold is not associated with significant morbidity or complications.

**Option B:** While blood loss exceeding 120 mL may be more severe, the definition of menorrhagia is specifically based on a threshold of 80 mL, not a higher value.

**Option C:** There is no established definition of menorrhagia based on blood loss exceeding 60 mL, and this option is not a valid definition.

**Clinical Pearl / High-Yield Fact**
It is essential to note that menstrual blood loss can be estimated using a pictorial bleeding assessment chart (PBAC), which provides a more accurate assessment of menstrual blood loss than a single measurement.

**Correct Answer: C. 80 mL**