You won't be pregnant forever (as much as it feels like it) so there is no need to buy a completely new wardrobe. You do, however, need a few pieces to make sure you are comfortable while your body undergoes some big changes. Comfortable is the key word here because when you are nine months pregnant that is all you will care about. You will want your maternity clothing to fit from the time you are starting to "show" til the end when you feel ready to pop.
Nice Jeans- There are some amazing maternity jeans out there that are flattering and stylish. I personally loved the maternity jeans with the huge band that came up over my belly; they fit perfectly and really accentuated the best parts of a pregnant body. Invest in some nice jeans. Jeans go with everything so you will get good use out of them.
Plain T- It's important to have some plain T-shirts or tank tops. You can wear non-maternity jackets and cardigans to dress them up and give variety to your wardrobe. Also, if you are hot all the time, like a lot of pregnant women are, it's nice to be able to have a light shirt or tank top to throw on.
A Nice Dress- Every pregnant woman looks beautiful in a nice dress. Get yourself a dress that fits and flatters your figure. A dress made of light material that flows will make you feel lighter than you are.
Maxi Skirt- Maxi skirts are very in right now and they look so cute with a little mama belly! Maxi skirts are feminine and comfortable. Plus, when it gets hard for you to shave your legs you won't have to worry about it with a maxi skirt. You need a maxi skirt!
Flip Flops-You need some flip flops or comfortable shoes that you can slip on. They may not be the most stylish shoes but your feet can swell up and flip flops might be what works for you. I had my baby in July and all I wore towards the end was flip flops. I love the Old Navy flip flops because they are so cheap and provide a little more support than some of those really flat T strap sandals that are popular right now.