Pituitary enlargement during Pregnancy

MRI mid line sagittal T1 image showing pituitary gland with ~11mm height in a 9 month pregnant female attributed to normal physiological enlargement of pituitary during pregnancy. 

The size of the pituitary gland varies with age and sex.
In its size the most important para meter is its height which is most often affected during physiological as well as pathlogical conditions.
Normally on an average height is between 3 and 8mm.
The height increases during adolescence due to normal physiological hypertrophy.
Generally larger in females than males.
There is slight increase in size seen during the sixth decade in females.
The most striking physiological changes seen during pregnancy when the gland progressively enlarges reaching a maximal height immediately after birth when it may reach 10mm in height.
Reference : Endotext, Radiology of the Pituitary, Jane Evanson, MD