The authors present the clinical aspects and changes of the pituitary gland and adenomas in pregnant women by MRI. A number of physiological morphologic changes are seen during pregnancy. Moreover, the hormonal milieu affects patients with adenomas which could evolve leading to severe complications as hypertrophy, necrosis, and hemorrhage. An increase in the volume and T1 hyperintensity of the anterior pituitary, is normally seen. These changes are explained by an increase in lactotrops and prolactin production. Tumoral complications are more frequent with macroadenomas, and are suggestive of a sellar mass or apoplexy. Nevertheless, other differential diagnoses must be suggested in pregnancy and post-partum including hypophysitis and Sheehan syndrome.