Oh had a thought about maternity bras too. When I was being fitted the lady gave some great advice.

No matter when you go and buy them, ie four months five months etc, you should have enough hooks nad eye left to take you all the way through ie should be able to expand the bra one hook each month and one for after (does that make sense?).

Also, you should be able to put a fist in the cup size as well as your boob (for when they fill up after wards).

Seems to be working great so far.