In general, it is always best to wait until you are done having children before having a breast lift. Future pregnancies can stretch the result out and cause you to need to undergo another lift. Otherwise, a well performed lift usually lasts forever in terms of the nipple and areola staying up above the level of the inframammary crease. The breast may lose volume with time and need an implant to fill out the lost volume.
The keys to preserving the lift really lie in the nature of your skin and keeping a stable weight profile. Inherently, a person who needs a lift has demonstrated that their skin doesn't have good elasticity already and there isn't anything they can do to improve it other than preventing wide weight swings and by wearing supportive garments.
