Hi Sara - I am 12 weeks (tomorrow!!) pregnant and have noticed my breast size has increased but it just means I finally fit into bras that I wore BEFORE i fell pregnant with Marnie. I was fitted at Myer - (who were terrific!) at around 4 months. The lady fitted me with a maternity bra and showed me how to increase it as the pregnancy wore on and then how to decrease the size around my middle after I had the baby. It was very comfortable (i bought some cheap sports singlets to wear to bed as my breasts were very uncomfortable.) I think it was a triumph.
At around 7 months I was getting very sick of my maternity bras and went to Target and fitted myself with a couple of 'pretty' bras. THis was a great confidence boost and also meant I had 'newish' bras to wear after the birth.
I breast fed for 12months and I still wore my maternity bras until the last day.
Good luck. I suppose my best advice is to get fitted!