Since bras are made symmetrically, some compromise must be made from the start. Most women increase one size in girth and one size in cup size, but again, there are no guarantees. There is some controversy about whether or not underwires are appropriate for nursing bras. If you can get good fit and sufficient support without an underwire, that is usually best . Keep in mind that most fashion bras compromise on support for looks - and therefore need the underwire to make up the difference.
Most nursing bras have the extra support built in whether softcup or underwire.
Another important consideration is that in the last few months of pregnancy rarely will any underwire be comfortable, especially when you sit down and it pokes into the baby. You may want a comfortable softcup for lounging around the house and an underwire for when you are going out and want to look a little perkier. It doesn't come up as high in the center so there is less chance of it protruding outward - even though all styles should stay close to the breastbone. Even more importantly, the wire should not protrude on the sides where it could chaff the arms as they swing. The most popular fabric for nursing bras is cotton - and with good reason.