Altering fashion patterns to make maternity clothes is relatively simple -- and can save you money by precluding the need to buy all new patterns. This also comes in handy when maternity patterns lack your sense of style. The quantity of regular sewing patterns always outnumbers that of maternity patterns so being able to alter patterns for maternity wear increases the options available for making clothes. If you're not familiar with sewing, stick with the basics before advancing to major pattern alterations; this will help you to avoid frustration and wasting money.
Decide on the pattern that will be altered, open the pattern pieces and cut out the pattern pieces necessary to complete the desired clothing. There are two options: pattern pieces can be taped to tracing paper (which is similar to the paper patterns are made of) and then the alterations are just added on to the original pieces; or pattern pieces can be traced onto large sheets of tracing paper where the alterations are added and new pattern pieces are cut, preserving the original pattern pieces for later use. Either way, the alterations are basically the same, but if tracing onto paper and making new pattern pieces, do this before moving on to the next step.
If preserving the original pattern is not necessary, tape large sheets of tracing paper to the pattern pieces where the extra room is added based on the following steps.
Look at the pattern pieces for a top, blouse or tunic. Note where extra room is needed; this may be in the bust line and below. Alterations must be made on all adjoining pieces to allow the clothing to be assembled properly. If the original pattern still has the lines for larger sizes, use these to increase the bust of the top. If the original sizing lines were cut, use tracing paper (taped to the pattern) to extend the bust region -- providing the desired extra room -- and make the addition on all pieces covering the bust region and back of the top.
To determine the needed room, look at the original packaging envelope for the pattern. On the back of the pattern envelope the final measurements for the outfit will be presented, according to the original sizing. If the original size provided a 35-inch bust -- and a 38 inch is needed -- add about 1.5 to 1.75 inches to all of the bust pieces, including the back portion of the top.
Locate the portion of the pattern that extends down and covers the abdomen, which will clearly need enlarging for maternity wear. Using attached tracing paper, extend the front, sides and back of the top as much as needed, gradually increasing from the bust line to the bottom edge. Usually 2.5 to 2.75 inches is enough when added to all pieces. Also, extend the lower edge of the top, blouse or tunic a couple of inches to allow for the extra room and lift (of the shirt) by the expanding belly. Extend the lower edge on all pieces. Also extend the lower edge of the arm hole outward to accommodate the bust and belly expansion.
Make the pants, skirt or bottoms according to the pattern's instructions; but use a maternity insert for the front of the bottoms or skirt to allow for the belly expansion. Inserts -- consisting of a comfortable elastic or stretchy fabric -- are the easiest way to alter a bottoms pattern.