How to pick bras:
As your breasts will get fuller and larger specially in your third trimester, you shouldn't try hard to fit into your same bras. Usually expecting women grow a cup size, if not more, during their pregnancy period, so as soon as you feel that your breasts are snug in your bra, consider it a sign to shop for a new one.
You can still feel sexy by wearing pretty lingerie during your pregnancy by simply going for a regular bra, but one size bigger. Another option is maternity bras, which have wider straps for extra support, are equipped with soft lining and don't include under-wire cups for more comfort, which is the less pretty option.
You should own at least three bras to wear during your pregnancy, try to have a selection of beige, white and black to suit your basic wardrobe needs. Also note that your bra size can change several times during maternity, it's very possible to grow up to two cup sizes when you're approaching your due date. To extend the life of your maternity bras, in case the cup size is fine, but the band isn't fitting well, you can use a bra extender, which will elongate the bra band a few extra centimeters.
How to pick panties:
When it comes to panties, you also have several options to pick from when you're pregnant. Your sexy panties that are already in your lingerie wardrobe would only fit during the first trimester, where your belly hasn't grown much yet. For your second and third trimester, you should start shopping for new panties. You can go for low-cut panties such as thongs or bikinis, that would go under your growing belly, or high-cut panties that go over your belly covering it completely. It's true that high-cut panties aren't the most flattering underwear that you can pick, however it's the go-to choice for many pregnant ladies as they're comfortable, so the key is to pick soft, stretchy fabrics that won't irritate your belly.