Most women are understandably reluctant to buy a winter coat that will see them all the way through pregnancy and may well never be worn again. The good news is that you probably won't need one at all! You are likely to feel very warm toward the end of your pregnancy, and may find it more comfortable to wear plenty of layered knits rather than one warm coat or jacket. Layers can also be easily discarded if you become overheated while you're traveling.
You can also probably hijack some of your partner's wardrobe, and borrow a coat or jacket that will fasten over your belly if you're planning to be outside for extended periods. Alternatively, go to a local second-hand shop-you may well find a larger coat or jacket for a bargain price that will last the few weeks of your pregnancy.
Another thing to consider is wearing your own coat unfastened, with a long scarf hanging down to fill the gap.
Think about purchasing a large shawl or wrap, which will see you through the winter months, and keep you and your baby warm after the birth. Shawls and wraps are ideal for keeping you warm when your baby is in a sling, and also for unexpected breast-feeding sessions outdoors.
You'll need to be extra careful in the winter, when you're in icy conditions. Make sure you wear sensible flat shoes when you're out and about to reduce the risk of slipping and falling.