A few years ago a friend's mom worked at a clothing store that was going out of business. He gave us a pair of 33x30 men's pants from their closeout in hopes that we could use them or pass them on. They were too short for Tom and too big for me. I didn't know anyone who could use them so I put them in the fabric pile and figured I'd do something with them eventually. Turns out now was the perfect time to pull them out, chop off the waist, and convert them to maternity pants.
First, I removed the zipper:
Next, I sewed the fly shut and marked my cutting lines in white. In the back I cut 1" above the pockets=1 3/8" below the waistband seam. In the front I marked where the elastic should meet the fly when I was wearing the pants and curved out to meet my measurements across the back.
The back in the midst of cutting...you can see the cut line marked. Another important step is to baste across the top of your front pockets and the side seams about an inch below the cutting line. I didn't do this before I cut and they gaped open and made it difficult to cut evenly. I ended up basting and realigning to make sure everything was even. I did the "one leg inside the other" trick to make sure the front was cut evenly (as if I were sewing two halves of a pair of pants together at the crotch seam).
Because these were men's pants the pockets were huge...both wide and deep. I made them smaller.
Added elastic that I measured to fit using a comfy pair of maternity pants. Marked in eighths to evenly space around the waist, stretched and sewed in place with a 1/2" seam. I have previously used elastic belting, but when my husband went to JoAnn Fabric* to get me more, they had no idea what he was talking about (despite my buying it there a week ago and sending a swatch.) This is 2" elastic but it is thinner and a bit more stretchy. It is a little loose but I'm only ~21 weeks so I'll consider it growing room.
Finished...ignore the stretch mark scars around my belly button...they showed up when baby #3 hung out until 42 weeks!
And from the side:
*My husband graciously went to JoAnn today after church because I was home with a sick kiddo. I had Christmas coupons to combine with sales...he bought me 14 zippers, 3 spools of thread, and my elastics based on a swatch card and his finely trained artist's eye. He rocks!