Fit, how the cup conforms to the shape of the breast, is the most important consideration when choosing a nursing bra. It is often ignored or compromised because of ignorant sales help, limited selection, or the marketing of less important aspects of the bra. After trying on one or two styles in ten different locations, frustrated very pregnant women and moms with new babies sometimes settle for anything that comes close. Fitting may be difficult because breasts are rarely symmetrical in size and shape. 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.