If your nipples are flat or they retract, which means just that they've pull back slightly, or they're severely inverted where they just don't pop out at all, you can absolutely still breastfeed. Because all we need to do is get the baby, we don't want the baby on the nipple. We want the baby behind the nipple.
So as long as they can grasp enough of that breast tissue in order to form a teat with that tissue then that's all that matters. The milk will come out regardless.
If we were letting them glide right on yes, they'd be frustrated. But if from day one that's all they know is that you have an inverted nipple we can easily get them back far enough so that they can still have that spray of milk coming out.
With large nipples, there are some women with very, very large nipples, with large nipples it sometimes really is an issue with getting the baby's tiny, tiny little mouth around that. So sometimes it takes a little bit of patience in waiting for the baby to get just that little bit older, that little bit bigger in order to be able to grasp around that area.
If not you might end up with a little bit of nipple soreness because that's all they can grasp in their mouth for the time period, for the time being. But it doesn't last long. And as long as you continue to put them on it's all they know to begin with and it's going to be absolutely fine.
If you do have flat or retracted or inverted nipples and you want to try to train the nipple to come out you can purchase a pair of breast shells to wear in your bra about the eighth month, during your eighth month of pregnancy in order to train the nipple to actually pull out. It just puts a little bit of pressure around the areola to sort of pull that tissue, to pull that tissue out. And that can help.
But if not, not a big deal at all. The baby will be able to still nurse.