During the pregnancy, the fetal-placental unit secretes proteins and steroid hormones into the mother’s bloodstream and this affects almost every endocrine gland in her body. It is well known that the pituitary gland is enlarged during pregnancy which is mainly due to diffuse and nodular hyperplasia of lactotrophs. Although pituitary adenomas, particularly prolactinomas, are no more numerous or larger in pregnant patients than in normal male and nonpregnant female subjects the hyperplasia of lactotrophs may have important clinical implications for the patient with a pre-existing prolactinoma. An increase in pituitary volume of more than two fold during pregnancy may make the pituitary gland more susceptible to ischemic necrosis after severe postpartum vaginal bleeding. Hyperplasia of the lactotroph cells stimulated by estrogens produced by the placenta and progesterone during pregnancy causes the pituitary to outgrow its blood supply, and may be a contributing factor in the development of postpartum pituitary necrosis (Sheehan’s syndrome). On the other hand, hypopituitarism developing during pregnancy may also be caused by lymphocytic hypophysitis and the differential diagnosis between these two disorders have paramount importance. The diagnosis of lymphocytic hypophysitis should be entertained in women with symptoms of hypopituitarism or mass lesions of the sella during pregnancy or postpartum period, especially in the absence of a history of obstetric hemorrhage. Pregnancy is associated with a lowering of the osmostat, the set point for plasma osmolality at which arginine vasopressin (AVP) is secreted, by 10 mOsm/kg. Thus pregnant women experience thirst and release AVP at lower levels of plasma osmolality than non-pregnant women. Borderline diabetes insipidus may manifest or the disease worsen during pregnancy because of increased vasopressin degradation caused by markedly increased levels of placental vasopressinase and pregnant women with diabetes insipidus should be treated appropriately. In conclusion, although the endocrine changes associated with pregnancy are adaptive, however, a woman may develop overt signs of a disease as a result of pregnancy.