Feathers Flights // Sewing Blog: Maternity Swimsuit: Pattern Alteration Tutorial


Maternity Swimsuit: Pattern Alteration Tutorial

The first step in making the Grow With You Maternity Swimsuit is to alter a pattern. I used one of my own drafted patterns that I perfected in my college swimsuit class, but I've made it easy by finding a couple of swimsuit patterns that you can easily use. You could even draft your own if you'd like. Basically, you need to find a swimsuit pattern that has an empire line in the front.
The first one on the left is a FREE swimsuit pattern from Burdastyle. I've used it before and my advice would be to make a mock-up or two because it's a short torso pattern.
The middle one would work just fine, if you don't use the dress pattern.
The third one would only work if you used the halter pattern.
These next two would work well if you converted them into one piece suits. I've used the one on the right which you can see here. I love the look of the bodice even though it's a little tedious to make.
Once you have your pattern, you are ready to begin. Start with your lower torso front and back pieces.
Straighten out the waist of both front and back by drawing a straight line from bust to hip. I did this because I've found I've lost my waist. It also gives you side room to grow.
Do the same on the back
Measure the length of the center front of your front piece. Mine measured 14". Measure yourself from just under your bust to the top of your pelvic bone. If you know how big you get, you will have a good measurement. I guessed at how big I was going to get. Compare the two numbers. Because I wanted to put in lots and lots of gathers, I decided to do a 3:1 ration meaning I'm going to add 2 inches every 1 inch.
Add width to the center front of your front piece. I guessed on this too. I'm going to count on the stretch in the fabric if I'm bigger than this.
Next, draw a perpendicular line where you want your gathering to stop. I wanted mine to go all the way to the top of my legs so that's where I drew my line.
Cut on the line you just drew. Add 1/4" seam allowance to the two pieces you just cut!
Put the bottom piece aside. On the section you want gathered, draw a line in increments that you previously decided. My ratio is 3:1 so I drew an line every inch. Number each piece and draw a line a couple inches in from the old, straight center front line. This is your grainline.
Cut on every line, so I ended up with 12 pieces. Decide how much you want gathered on the side seam of your suit. I only wanted 2:1. I wouldn't do any more than 2:1 in the side seam. That much is almost too much. Starting at the bottom, tape your lowest piece onto the bottom right corner of a piece of paper. (You may need to tape lots of pieces of paper together if you have a big ratio like me.) Draw the grainline up more than 2 inches. Measure up 1 inch at the side for 2:1 ratio, and 2 inches up in the center for 3:1 ratio. Draw a line from mark to mark, this is the line you'll match your next piece to. Make sure to match up the grainlines (the two red dots) even though they aren't going in the same direction anymore.
Keep doing this for each piece, making sure you match up the grainlines. See how the grainline changes direction at each piece? This is because you're adding more space to the center front then the side.
After you're all done, you should have a big piece that looks like this. It's a big curve.
Next, you need to straighten out your curved center front line. To do this, draw a new line from the middle of the old line to the middle of the next line. In this picture the black lines are the old lines. The red dots are the center of each old line. The blue line is the new center front line.
Last of all add a 5/8" casing the the center front. Then cut out your new torso piece. You're done with the pattern alteration! Next is the swimsuit construction.
Please, please email me if you have any questions! I want to help you!


  1. You are so AMAZING and TALENTED!

  2. This is so incredible that I got totally lost! Way beyond my skill set. But someday I hope I can make one. :) Enjoy yours!

  3. That seems so much easier than I thought it was going to be. How cool! Way to go!

  4. This is awesome! I had no idea what to expect, but very detailed and clear instructions - my favorite. :-) Now just to get it finished before the baby gets here...

  5. wow sooo much work!! But it really looked so cute on you.

  6. This is fantastic!! I'm soo jealous you took a swimsuit class in college---remind me why I studied English again?! And do I spy the duck pond on 8th?:) You look really familiar to me! I think I must have seen you around!

  7. Once again Heather, something of yours in being featured on SewSet today! I keep clicking on things, and then when I go to find out whose it might be - they turn out to be yours. Fantastic stuff, so different then the norm. I love it! Thanks for sharing!
    - Jess, SewSet.com

  8. Such a talented one, I love it. I wanna try this pattern too. Thanks for sharing.

  9. Thanks for the great idea and tutorial, I am planning to try it. I am just wondering one thing - obviously the added length in the torso is gathered in by the ties. But you also added width (the belly curve). What gathers that in before you are "full size"? It seems like that would be baggy until your belly grows to that size. What am I missing?

    1. I add a little to the side but not enough for it to be baggy. Swimsuit fabric stretches a ton so you don't need a whole lot of width. The fabric will stretch all by itself.


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