I had terrible problems because of inverted nipples. Everyone (midwives, health visitors, breastfeeding advisors etc) said it shouldn't be an issue, but thats rubbish. It was awful. Poor DS couldn't latch on at all, I was ripped to shreds and he lost weight and was jaundiced. No matter how much they told me the positioning etc was fine, he just couldn't do it, it was like sucking on a football bless him. In the end the only thing that made it possible was using nipple shields, they were a life save. If it wasn't for them I'd have stopped after a couple of weeks. As it is, at 20 weeks I'm still going with just one bottle a day. And I no longer use the shields either.
I have inverted nipples too. Baby 5 weeks old on Thursday. Rubbish support in the post natal ward and was discharged on the grounds we fed her formula. We did this for the weekend, reluctantly, and managed to get to a breastfeeding clinic on the Monday. They lent us an electric pump and I've been double expressing 6 or 8 times a day since. With the help of the clinic, we attempted latching on a few times each week, until last week when baby/ I finally cracked it (on one breast only so far). Now breastfeeding successfully on that side. The specialist at the clinic believes that lactation and pumping helps to alter the tissue to make the nipple more flexible. It now takes one painful suck from baby to make it come out, then I latch her on properly and we go from there. Maybe the expressing regime isn't for everyone, but it worked for us and I'm really pleased that we managed to keep it up in order to get this far. We have high hopes for the left breast now!