Shops will tell you between 8 - 12 weeks as thats when you start to change size / need more support. Personally, I couldnt wait to get out of underwired as I hurt so much anyway... Just do what feels right. Any soft bra in pregnancy is good - maternity ones can be more expensive.
Bexie I have never gone back to underwire as after finishing bf dd by boobs shrunk from dd to an 'empty' c. Now they are HUGE again and I wear sports bras - cheapy one's from Matalan and Asda 5 each I think. They would not give me enough support for running but for eveyday and they wash up lovely!
Congrats btw carrielou, was meant saying on the pushchair thread!
The bras I have atm are a 44DD and are undwerwired. I have a rather limited choice of where to get bras from really. I'm not sure if Evans do maternity/nursing bras and am not sure how big M&S go upto. I think a good starting point will be to look for my old Mothercare ones for a size, although I have put on weight since I had Tom . Or just go and be fitted, which will mean a trip into Glasgow.
I was told that too bumpsoon - and believed the m&s women who then sold me the two most uncomfortable bras I have ever ever worn. Would never go there again!
It is important to keep properly supported, the advice against underwire is that your breast tissue is soft and the underwire could hurt you. Personally I wish i had not listened to her and stuck to them, as they are way more comfortable than any non wired bra in my opinion.
As for nursing bras - next do them - pretty and comfortable but not very supporting. The m&s nursing bras are HIDEOUS and were hugely uncomfortable.
I was a 32D pre pregnancy and went up to a 32E at about 8 weeks - couldn't wear my normal bras anymore as they just didn't fit. So I had to get mine then. (frist pregnancy) also I def wanted to protect them as soon as possible - limit any pregnancy damage IYKWIM