Extra yardage + notions: You will need enough material to cut an extra midriff piece and two 2" wide bias strips. The length of these will vary based on your size -- you'll need enough to cover the bottom edge of the bodice. Fifteen inches gave me plenty. You will also need some sew-on snaps.
Notes on the pattern: The pattern layout suggested by the instructions has pattern pieces facing both directions, but my suggestion to you is to lay out all your pieces facing one way. Even if there is no obvious direction to your fabric, any differences in the way the fabric looks may not be obvious to you until you see the pattern pieces sewn up together side-by-side. I was able to cut all my pieces facing one direction without using much extra fabric at all. In fact, I found 2-2/3 yards of 55" wide fabric to be just enough for this dress, even with my nursing changes and using the 3/4 sleeve option. (I cut out a size 16, for reference. I did not lengthen the skirts although I did shorten the bodice and back pieces by about one inch.) If you'd like to see a sketch of my layout, click here.
I also recommend perusing the posts under Casey's Swing Dress Sew-Along for extra helpful tips. She will walk you through the notoriously tricky facings on the bodice. (Although even doing it her way, I still ended up with some problems -- the biggest being that the front facing crease no longer lays on the grain, thus causing it to be prone to stretch. I added some iron-on interacing to help stabilize it; you may want to do likewise if you run into that problem!)
So without further ado, let's begin the nursing changes!
Follow the instructions as given until you get to step 6. Omit the directions to "lap right front over left, matching centers. Baste lower edges together." Continue on until you get to step 9.
1. Measure the distance between the notches on the upper midriff.
2. Gather the lower bust on the bodice to match your first measurement, securing the gathering stitches in place. Staystitch over the gathered section (this means stitch with a normal stitch length at just under 1/2" away from the edge).
3. Take your two 2" wide bias strips and press them in half, lengthwise. Fold in the edges to the center crease and press again, being careful not to obliterate the center crease. You should have three creases, 1/2" apart, down the length of your bias strip.
4. Pin the bias strip to the bottom of the bodice piece, with the right side of the bias facing the wrong side of the bodice. Be sure to leave some extra bias tape at the center edge of the bodice. Stitch, 1/2" from the edge. Before you cover the raw edges with the bias binding, mark where the notches are on the bodice bottom with pins, chalk, or tailor's tacks.
5. Trim the raw edges of the bodice and bias tape (although not the extra bias tape at the center front -- we'll get to that part in a minute). Fold the bias strip over and, with the free edge tucked under, pin in place on the right side of the bodice fabric. Fold the extra bias tape hanging off the center edge of the bodice inward to create a nice finish. On the right side of the bodice, stitch the bias tape down, 1/16" from the upper edge.
6. If you want to interface your midriff piece, do so now. Mark where the notches are on the upper midriff with pins, chalk, or tailor's tacks. Then pin your two midriff pieces, wrong sides together, along the upper edge. Stitch, 1/2" from the edge.
7. Press open the seam you just sewed (a tailor's ham will make this easier, but even if you don't have one, don't skip this step!). Clip and trim the seam allowances, then turn the midriff pieces wrong sides together and press the stitched edge flat.
8. Topstitch the upper edge of the midriff, 1/16" away from the edge.
[Sorry about the funky lighting -- there was no daylight left by the time I got to this step!]
9. Pin the bodice pieces to the midriff, matching notches. You will want to pin in such a way that the edge of the midriff just covers the bias tape of the bodice pieces. You may want to hold this up to your bust to experiment with how far over you can stitch and still have the bodice open up far enough to nurse. I was able to stitch to the inner notch on the midriff piece.
10. Carefully sew over the topstitching on the midriff, stopping at the inner notch (or wherever you stopped pinning). A tip on re-stitching your topstitching: it is a temptation to watch the needle while sewing, but if you watch the guide line on your presser foot, your stitching will be much more accurate.
[How the dress will look from the inside.]
11. Mark positions for the sew-on snaps on the rest of the bodice edges. First, sew snaps onto whichever side of the surplice bodice you want to be in front. The corresponding snaps will be on the inside of the midriff. Then, sew snaps onto the side of the bodice that will be behind the first. The corresponding snaps to this side of the bodice will be on the back of the front bodice.
12. Press the inner midriff piece (the lining) under 1/2 inch. After attaching the front skirt pieces to the outer midriff piece, slipstitch the inner midriff in place, neatly covering all raw edges.
That's all! Finish the rest of the dress as directed in the original instructions. Let me know if anything in my tutorial is confusing or unclear, and I'll try to address it. Happy sewing!