I was told with my first son that I couldn't use shields til milk supply was in.

This last time my midwife was also an expericed lactation consultant, she said I could use the shields from the beginning just to help stimulate the breast. I was also expressing, both by hand and with pump as often as possible to get colostrum and also help milk to come in. I found this worked really well as milk was in by day 3. Whereas with first son I wasn't allowed to use shield til milk was in and that took a lot longer because he wasn't attaching to the nipple at all.
BTW: Some of the other midwives in the hopsital disagreed with this method, but I stuck withit and it worked.