The lack of vasopressin can develop during pregnancy if the pituitary is slightly damaged and/or the placenta destroys the hormone too rapidly.  This type of vasopressin deficiency is called gestagenic or gestational DI and is treatable with DDAVP but, in this case, the deficiency and the DI often disappear 4 to 6 weeks after delivery at which time the DDAVP treatment can usually be stopped.  Often, however, the signs and symptoms of DI recur with subsequent pregnancies.