Beginner tutorial to make that maternity shirt a long-term staple in your closet after your done being pregnant.
Step 1: Cut Along Side Seam on Back of Shirt
Turn the shirt inside out, so right sides are together. Cut up along each of the side seams just past the ruching, as shown below.
In the photo, you can see the shirt with both side seams cut only up to about the chest area, a few inches under the underarm of the shirt.
Step 2: Cut Along Seam on Front of Shirt
After cutting up the seams on the back of the shirt, cut along the open seams on the front of the shirt right up against the manufacturer's seam to remove the stitching and ruching.
Step 3: Pin Up Sides
In the photo, the shirt is lying face down (the front side has more fabric and is lying directly on the cutting mat). Carefully lay the back panel of the shirt over the front panel and pin up each side. Remember from Step 1 that the shirt should be inside out so that right sides of the fabric are together. I also had to be careful to line up the stripes. This would be easier with a solid color fabric that wouldn't require as much precision to piece back together.
Step 4: Sew Up Sides
Sew up each of the side seams along the new edges of the shirt that you pinned. Start the new seams a couple of inches above the end of where the fabric was cut. Below, you can see I cut the fabric up to where the blue pin head sits. I started my new seam about two inches above this point so I could more fluidly transition from the existing seam to the new seam.
Step 5: Finish Side Edges
These two photos show the shirt with new seams lying inside out and facing down on the cutting mat. Turn the shirt right side out and try it on to be sure it fits. If not, rip out the new seams just completed as needed and redo with new seams. If it does fit, turn the shirt inside out so right sides are together, cut off the extra fabric along the sides and serge or use a zigzag stitch along the new seams to finish them.
Step 6: Finish Bottom Hem
In the top photo, you can see the front of the shirt (lying directly on the cutting mat) is much longer than the back of the shirt (folded up slightly) after removing the ruching. Cut off the excess fabric on the front of the shirt to make a hem that matches the existing hem on the back panel.
In the bottom photo, the shirt is flipped over so now the front side is face up, still inside out (i.e. right sides together). Fold the bottom of the front panel twice creating a hem and straight stitch along the bottom to match the existing stitch on the hem on the back side.
Step 7: Wear!
Here is the shirt both tucked and not tucked so you can see the details of the finished product.