There are a few differences between maternity tops and regular women's clothing. Maternity tops are typically longer and have extra fabric to accommodate a large belly. Most are made of a stretchy material such as spandex so your top grows as your stomach does. Many maternity shirts can also be worn for what is known as the fourth trimester, which refers to the few months after the birth of your child when you may not fit into your pre-pregnancy clothes. These shirts also work well for nursing if they are a button-down, V-neck or cross-front style.
A way to save money is to evaluate your current wardrobe to see what you can use through your pregnancy. Shirts that are stretchy and long are most likely to work for most of your pregnancy. Empire-waisted shirts are flattering on the pregnant body and help define your shape. Cardigans, shrugs and boleros work as well, since they do not have to fit around your belly. Button-down tops and tight, stiff fabric do not work once you have passed your first trimester.
Many online tutorials can help you turn wardrobe staples into maternity clothes. If you can sew, you may find it easy to make simple adjustments to your favorite clothes that can help you keep your style during pregnancy.