I was recently told about an online brand called Pink Blush which not only carries Plus Size wears, but also Plus Size MATERNITY! 
While I've not had the need for such a purchase, I have heard from friends the struggles of being pregnant only to discover that maternity clothing is straight sized. 
In addition to the discovery of the online retailer, I was pleasantly surprised to find that the plus size items listed are in fact the same as the straight sized fashion, but slightly altered to fit a fuller figure! 
Check 'em out for yourself and leave your thoughts in the comments!