I am hanging out on the East Coast this week and while visiting a friend and her new baby the other day, she (the friend, not the baby) asked about my jeans - she liked them and wondered if they come in her size - 12 or 14.
I was wearing a pair of Joe's Jeans in the 'Rocker' cut (many brands now name their styles rather than using numbers, because it makes it much easier to know which one you like), which means they are pretty straight through the hips and legs, with a low rise. The low rise is not for everyone, and for a new mother I would generally recommend a mid-rise or regular rise jean for several reasons, the first being your body is not yet back to what it was - not necessarily fat, just different, and you don't want to flash your underwear at play-dates or mom-and-tot classes every time you sit down or bend over.
Anyway, back to the jeans - a brand like Joe's Jeans comes in sizes up to 32 which is equivalent to about a 12, and they do now have high rise styles which can allow women to breathe a little easier, as do the now-popular wide-leg styles. I think what my friend really liked about the jeans, and the reason I like the style so much, is that the straight-leg jean is universally flattering. It means that from the hip to the ankle, the leg stays pretty straight which is ideal particularly for women who prefer to camouflage their hips.
Nordstrom has other brands of jeans with similar styles that also go up to a size 14, take this pair for instance:
These Christopher Blue "Lloyd - Farrah" jeans look a lot like the joe's Rockers I was wearing and they are a little cheaper ($148) and go up to 14.
There is also the brand "Not Your Daughter's Jeans," which come in this great high-rise wide-leg style:
These are $108-$118 and come in sizes up to 18.
Of course if you have a very young baby and are still losing baby weight, you might not want to spend that much on jeans that you'll only wear for a couple of months (but might want to keep them for the next time you are pregnant) The Gap and even Old-navy have mid-rise, wide-leg styles.