So first step's first. Find yourself an extra large, comfortable sweater! This is a size 3X, which means it's long enough for me to wear as a tunic. I've decided I'll be living in pregnancy leggings (the thick winter kind) and these two will make a great combination. With some nice boots. And a scarf. Something easy and effortless, like this - only pregnant:
The first thing I did was put on the sweater inside out. I felt along the side seams and pinched everything in until I felt I had the right fit. Then I pinned it.
The rest is easy! Sew where you've pinned, cut off the extra and try it on. If you don't need to make any more adjustments, go ahead and zigzag stitch to 'finish' the seams. If it's still too big, take in the sides little bits at a time until you have the desired fit.
Voila!