As you know, we're expecting. I'm 26 weeks, so regular clothes don't really fit anymore. I thought I'd try my hand and converting a pair of my work slacks into maternity pants.
Here's what I did.
Turn the pants inside out. Find the center and fold. You want the middle of the back to be on one side and the front closure on the other. (See pic.) Pin the pants together at the top, so they won't separate or slide around. Then pin down at a curve to just below the zipper.
When these pants are on, the zipper falls at the bottom of my maternity shirts. If your zipper is longer, you may want to sew the zipper section shut and then cut where you want the bottom of your maternity band to hit.
Cut along where you pinned. I actually cut a little above where I pinned, because I didn't want to cut to much. You can always cut more if you need to.
Using a jersey fabric, or another stretchy fabric, lay your cut out section on the fold and pin. You want to make sure you fold your fabric in half and make sure the cut section is near the fold. I move it back about a 1/2" to allow for the seam. When you cut, make sure to give yourself a 1/4" to 1/2" seam allowance, all the way around.
Unfold your section and pin back into your pants. The pants should still be inside out.
Make sure you leave an area at the top to fold over for a finished top seam.
Sew around the pinned section and sew down your top seam. At this point I tried on the pants to make sure they fit. When thy did, I sewed a section seam around the new section to secure it. You could serge the seam to make it look more finished. Since no one was going to see this, other than you and me, I didn't feel the need to take that extra step.
Turn your pants back right side out and admire your handy work.
Here's a close up of the seam.
Now that you can convert your pants, you should be able to convert shorts, skirts, etc... Happy sewing!