New Bras?

Serenity
When did you start getting new bras? I don't want to buy new bras and then grow out of those! I've been trying to make my current bras work but my nipple keeps slipping out!(Embarassing!!) I'm 14 weeks and 5 days. About how much longer will my breast continue to grow? Or should I just buy some a little big and see how it goes?