How do I tell her she has gone too fat without hurting her feelings?

My wife had our first child 9 months ago and she has recently been developing fatter and fatter by the day.

She is very emotional and I am thinking that I needed to convey to her that her new put on weight is offensive. I probably won’t have any desire to see her go stripped. I would prefer not to offend her so I am asking, whats the most ideal approach to let her know?