Which of the following is NOT a reason for gingival enlargement?

Gingival enlargement, also known as gingival hyperplasia, can occur due to several physiological and pathological reasons. Among the options provided, dehydration is not recognized as a direct cause of gingival enlargement.

During dehydration, the body's tissues, including the gums, may become less hydrated, leading to potential dryness or atrophy rather than enlargement. In contrast, pregnancy is associated with hormonal changes that can lead to increased blood flow and subsequent gum swelling. Vitamin C deficiency, while causing gum disease and potential bleeding, can also contribute to increased gum size due to inflammation. Similarly, leukemia can lead to gingival enlargement due to the infiltration of leukemic cells and the resultant inflammatory response.

Thus, while the other factors are linked to conditions that can result in gingival enlargement, dehydration does not contribute to this effect, making it the correct choice as the exception.