We get asked these three nursing bra questions daily at Evymama. Trust us, we've been there.
You may opt to shop only for nursing bras (which are bras that easily open with a clip for breastfeeding) and just skip maternity bras altogether! My best advice is that you do this when your bras start to feel tight, or when you hit 36 weeks of pregnancy, whichever happens first.
How many bras you buy is up to you, but I'm going to guess that you're probably not buying enough nursing bras to make life with a newborn manageable. One bra might as well be zero bras, because nursing bras need VERY frequent washing due to postpartum sweating (it can be extreme!) milk leakage, and little surprises like baby spit up. Two bras is barely better. The best solution? Allow for one on your body, one in your drawer, one in the washing machine, and one in the hamper waiting to be washed. That way you won't get caught braless, which can be a bit disastrous when you're leaking like a cartoon dam. Side note: a lasagna in the freezer is a good idea too, especially with a baby on the way. Being prepared is good common sense, as you know.
Finally, what to buy. You've heard that you shouldn't wear underwire when you're breastfeeding, or maybe not even in pregnancy? The truth is, underwire has a much-exaggerated bad rap. I agree that there are times when a soft, stretchy and malleable bra is your best choice. While your body is still growing, shifting, morphing, and filling with milk, it is likely wisest to steer away from underwire and stick to bras with some give. As your fundus rises, it's possible that the wires will sit right on top of your belly in your later months of pregnancy. Once your breasts have settled down a bit (a few weeks postpartum, unless you're doing lots of erratic feeding/pumping changes) you can look at underwired bras that will resemble your pre-baby t-shirt bras, if that's what you long for. The underwire in Evymama's nursing bras have varying degrees of flexibility, minimizing their potential impact on the breast. The real thing you need to look for, though? A great fit. An ill-fitting 100% cotton wire-free bra that isn't the right size for you will do more damage than a properly-fitted underwired bra. Unless you've had some trouble with plugged ducts and your IBCLC has told you to steer way from wire, you should be totally fine in that nicely-fitted underwired nursing bra. Just don't go falling asleep in it, or all bets are off. (Yes, you're probably going to fall asleep nursing your baby. Sweet dreams [in a soft cup bra, or braless!])
My final note: If you wear an XS, Small, or a Medium t-shirt, don't let anyone sell you a 38 or 40 band bra. They're doing this because they literally have nothing in their warehouse that is the right size for you. You're probably something like a 30, 32, 34, or possibly 36 in a cup that is higher than a DD, which chain maternity stores just DO NOT sell. We have bras in A to K cup size, as will (hopefully) other specialty bra shops. There's a reason that Evymama ships to far-away places like Nunavut.
Curious about your postpartum size? Check out my nursing bra fitting page here.