I used my favourite Burda yoked/cropped pants pattern to make this maternity version from a slinky knit. I made no alterations to the pattern at all, apart from adding some elastic to keep the pants up. Being slinky, the ended up a bit longer than the pattern - but since Winter is approaching that is a good thing!
I might have to see if I have any more knit fabrics that I can turn into maternity pants. These are so comfy to wear and easy to make.