Can I Increase the Size of my Existing Saline Breast Implants?

Thank you for your question.Technically,
you can do this.However, I would not
recommend opening the valve and refilling it.By going back to surgery and adding more fluid, it voids the warranty on the implant. Then,
you need to keep in mind that every time you go back in for surgery, you open
yourself up to complications like capsular contracture especially when you are
using the same implant.I prefer to
place new, sterile implants in to get the size you desire and minimize risk for
complications.I hope this helps.

This is generally not recommended for several reasons. The most important is that over filling a saline implant can cause it to become round and hard. You should go with a larger implant that will be more appropriate for the given volume you desire.

Adding saline to your existing implants violates the manufacturers warranty because the valve was only meant to be cannulated once.  This would put you at an increased risk of later deflation, with no warranty coverage.  The effects you are seeing are from postpartum breast shrinkage, which is normal.