Soalan ni sangat berguna buat saya sebab saya pun tertanya-tanya juga (saya copy paste saja yek, sumber: http://www.pregnancytoday.com/ )
The problem with underwire bras is that the wire will sometimes put pressure on an area of the breast that could cause a plugged duct. And the wires can come out of the casing and press where they don't belong at all!
The important thing to do is to get a good fitting bra, and if you are buying during pregnancy, it needs to be large enough to accommodate the increase in breast size that normally accompanies pregnancy and birth. Of course, much of that increase is due to the milk-producing glands and the milk getting ready for the new baby. There's also extra fluid, and usually, when your mature milk comes in (3 to 4 days after delivery), there's more than your baby will need. That will eventually settle down, and the extra fluid will leave as well.
So, bras need to be able to accommodate the increases during pregnancy, plus the increases due to extra milk and fluid production, and then the decreases after the first week or two. Some moms opt to buy bras during pregnancy and then again after baby arrives. Some buy bras that are a little bigger than necessary.
Whatever you do, get a good fitting bra. If you get an underwire bra, make sure it fits really well and that the wire doesn't put pressure anywhere. Don't sleep with this bra on!