Well, mine started in the second trimester, but I don't mind the odd yellow stain on my bra so haven't bothered with breast pads. They haven't done a full on big leak yet.

You can buy them now and if you don't need them for another 20 weeks or so (when your baby is out and your milk comes in) then you have them ready. You can get samples and wear them now to see which is the most comfortable and if you want to do washable ones or not.