Pregnancy and breastfeeding always have an impact on your breasts, period, because of hormonal changes and weight
changes, but implants
are pretty resilient. Silicone- or saline-filled; the outer silicone shell is quite tough. I've heard of demonstrations of cars being slowly driven over them! All told, though, we normally recommend that women wait until they have had had all the children they want to have devices implanted if they want to be sure they can breastfeed.