If your breasts sag a lot, then a breast uplift (mastopexy) with or without an implant will be recommended. With pregnancy and weight fluctuations, the skin of the breast gets stretched, and once the breast gets smaller, there is too much skin so the empty breast sags. To get a pert breast once more, you either need to fill the skin up completely again (augmentation alone), or make the skin small enough to fit snugly around the breast you have (mastopexy alone), or do both (augmentation mastopexy).
The scars for the breast uplift are more extensive and more visible than a breast augmentation alone. The scar goes around the areola and then vertically down to the fold, (you may see some diagrams that show a scar all along the crease or fold under the breast as well – resulting in an anchor shaped scar – but I don’t use this scar. We prefer a “racquet” or “lollipop” shaped scar, avoiding that scar along the fold completely).
The difficulty in trying to avoid the extra scars of mastopexy is that often a very large implant would be needed, and this means you need to be happy with a larger bust size, and be aware that you may will suffer from the weight of large implants on your back and neck, and that gravity will be working harder with the bigger implant to ruin your shape.