Pituitary Awareness Quiz: Day 4

 And we're on to day four! Today I have chosen not to do a multiple choice question, which is perhaps slightly evil - but equally it's a fairly easy question, so you should be fine. Ready, set.... Google!

National Pituitary Awareness Month Pituitary Awareness Quiz
Day 4, Question 4

Q.4: The human pituitary gland will vary in size over a person's life. What physiological event (other than untoward tumourousness) causes the pituitary gland to reach its largest natural size... and why?