LE, like a lot of catalog clothing, runs a bit big. I find once you get used to their sizing, it's pretty consistent- if you wear a 10 in LE for jeans- you'll likely wear a 10 in tops, dresses and even bathing suits unless you are seriously pear-shaped.
I have a couple of those dresses. They're not pleated in the back, they have a slight gather that allows the shirt to fall over your hips and butt (if you have them) without pulling the side seams back or being clingy. It makes it hand properly.
Can someone who is a size 6/8 or s/m at places like old navy comment on what size you got this dress in? Seems like a good deal.
Is it post pg friendly?
I am 4/6 depending on brand elsewhere and need an XS in LE. I bought a couple of these dresses in S when I was pregnant and they fit well then. I had them altered postpartum.